sensory evaluation manual

FOOD 3007 and FOOD 7012

SENSORY EVALUATION

MANUAL

Associate Professor Richard MasonThe University of Queensland

andStephen Nottingham

Sensory Evaluation

COPYRIGHT R L Mason and S M Nottingham2

ACKNOWLEDGEMENTS

These notes form the basis of a practical workshop presented for personnel at NaresuanUniversity, Phitsanulok, Thailand in July, 2002. We would like to thank Michael O’Mahonyfor his permission to include copies of the statistical tables from his book “SensoryEvaluation of Food: Statistical Methods and Procedures” and material supplied by the Centrefor Food Technology, DPI, Brisbane.

Sensory Evaluation


TABLE OF CONTENTS

ACKNOWLEDGEMENTS ....................................................................................................2

PROGRAM ............................................................ ERROR! BOOKMARK NOT DEFINED.

INTRODUCTION....................................................................................................................5

THE HUMAN SENSES IN SENSORY EVALUATION .....................................................7

THE SENSES - AN INTRODUCTION .................................................................................7

SENSE OF SIGHT- .................................................................................................................9

THE SENSE OF SMELL......................................................................................................13

THE SENSE OF TASTE.......................................................................................................15

THE SENSE OF HEARING.................................................................................................19

THE SENSE OF TOUCH .....................................................................................................20

SENSORY INTERACTION.................................................................................................21

OPERATIONAL PRINCIPLES OF SENSORY TESTING .............................................23

DESIGN OF A SENSORY TESTING AREA.....................................................................31

STATISTICAL PRINCIPLES .............................................................................................34

SENSORY EVALUATION METHODS .............................................................................38

AFFECTIVE TESTS.............................................................................................................38

SPECIFIC TEST METHODS ..............................................................................................39PAIRED PREFERENCE TEST.......................................................................................39RANKING FOR PREFERENCE.....................................................................................41RATING FOR PREFERENCE........................................................................................44

SENSORY EVALUATION IN CONSUMER TESTING..................................................46

ANALYTICAL SENSORY TESTS: ....................................................................................53

DIFFERENCE TESTING.....................................................................................................53

SIMPLE DIFFERENCE TEST............................................................................................53TRIANGLE TEST.............................................................................................................53DUO-TRIO TEST..............................................................................................................55TWO-OUT-OF-FIVE TEST.............................................................................................59

Sensory Evaluation


“A” – “NOT A” TEST.......................................................................................................59DIFFERENCE-FROM-CONTROL TEST (DFC) .........................................................59

DIRECTIONAL DIFFERENCE TESTS ............................................................................65PAIRED COMPARISON TEST ......................................................................................65RANKING TEST...............................................................................................................67RATING TEST ..................................................................................................................69

STATISTICS FOR SENSORY: DIFFERENCE TESTING .............................................73

DESCRIPTIVE TESTING ...................................................................................................76

STATISTICS FOR SENSORY: DESCRIPTIVE TESTING ............................................81

SELECTION, TRAINING AND MOTIVATION OF A PANEL.....................................86

REPORTING .........................................................................................................................91

SELECTED BIBLIOGRAPHY............................................................................................92

JOURNALS............................................................................................................................94

STATISTICAL TABLES......................................................................................................95

Sensory Evaluation


INTRODUCTION

Sensory evaluation - A scientific discipline used to evoke, measure, analyse and interpretreactions to those characteristics of foods and materials as they are perceived by the senses ofsight, smell, taste, touch and hearing.

Sensory evaluation was one of the earliest methods of quality control and it is still widelyused in industry. However, the level of application depends on the situation (e.g. beer andwine tasting to operators sampling of products from production line).

Four variables affect sensory evaluation:

• The Food• The People• The Testing Environment• Methods

Sensory evaluation terminology

• Sensory evaluation• Sensory Analysis• Organoleptic Analysis• Taste Testing• Psychophysics• Subjective Evaluation

Advantages

• Gives real answer regarding consumer quality• Relatively cheap process (depending on how it is done)• Rapid• Many applications• Objective methods are more reliable, accurate and reproducible. However, they must

be correlated to sensory evaluation to indicate a consumer response.

Disadvantages

• Time consuming• Expensive to run• Method selection• Analysis• Interpretation

Industry applications of sensory evaluation

• Product development• Product matching• Product improvement

Sensory Evaluation


• Process change• Cost reduction• New raw materials selection• Quality control• Storage stability• Product grading / rating• Consumer acceptance• Consumer preference• Panel selection / training• Correlation subjective / objective

Sensory Standards

Aus Standard Year Title

AS 2542.0 1995 Sensory analysis of foods - Introduction and list of methods

AS 2542.1.1 1984 Sensory analysis of foods - General guide to methodology -General requirements

AS 2542.1.2 1984 Sensory analysis of foods - General guide to methodology -Types and choice of test

AS 2542.1.3 1995 Sensory analysis of foods - General guide to methodology -Selection of assessors

AS 2542.2.1 1982 Sensory analysis of foods - Specific methods - Pairedcomparison test

AS 2542.2.2 1983 Sensory analysis of foods - Specific methods - Triangle test

AS 2542.2.3 1988 Sensory analysis of foods - Specific methods - Rating

AS 2542.2.4 1988 Sensory analysis of foods - Specific methods - Duo-trio test

AS 2542.2.5 1991 Sensory analysis of foods - Specific methods - 'A not A' test

AS 2542.2.6 1995 Sensory analysis of foods - Specific methods - Ranking

AS 2542.3 1989 Sensory analysis of foods - Glossary of terms

Sensory Evaluation


THE HUMAN SENSES IN SENSORY EVALUATION

THE SENSES - AN INTRODUCTION

The sensory properties of foods are related to three major attributes:

• Appearance - colour, size, shape;• Flavour - odour, taste; and• Texture - mouth feel, viscosity and hearing.

These attributes are expressed as a continuum and not as finite properties. It is impossible torate each one individually unless special precautions are taken, e.g. blindfolds, nose clips,coloured lights, purees.

Sensory Evaluation


Humans possess about 30 different senses. However, the sensory properties of foods areperceived through the senses of:

• Sight;• Smell;• Taste;• Touch; and• Hearing.

Stimuli

A stimulus is any chemical or physical activator that causes a response in a receptor, e.g. eyeis receptor for light, ear is receptor for sound.

An effective stimulus produces a sensation, the dimensions of which are:

• Intensity/strength;• Extent/separation;• Duration/retention; and• Hedonics/like-dislike.

Receptors

Receptors are the stimuli detecting cells of the sense organ, e.g. taste buds on tongue, lightreceptors in retina of eye.

Perception

Perception is the psychological interpretation of sensations determined by comparison withpast experiences, e.g. the sour taste of lemons is the perception of the sensation received bythe receptors (taste buds) from a chemical stimulus (citric acid).

Sensory Evaluation


SENSE OF SIGHT-

The appearance of food

Stimuli = visible lightReceptor= retina of the eyePerception=sight, vision, appearance

The appearance of foods is a major factor governing its acceptability and can be subdividedinto three main categories:

• Optical properties- colour, gloss and translucency• Physical form-shape and size• Mode of presentation-lighting packaging etc

Optical properties

Vision

Vision is a complex phenomena consisting of several basic components. A stimulus, light,from an external source interacts with the object and is brought to focus on the retina of theeye. The retina is the receptor of vision and contains two types of cells. The rods areresponsible for vision in dim light and the cones are responsible for colour vision. Lightincident on these cells causes a photochemical reaction that generates an electrical impulsewhich is transmitted to the brain via the optic nerve. Colour blindness is caused by loss orlack of colour receptor cells in the cones. Approximately 8% of the population have somedefect with relation to colour; mostly males.

Sensory Evaluation


Light

Visible light is that part of the electromagnetic spectrum which radiates between wavelengthsof 380 - 770 nm.

Different wavelengths produce different colours

380 - 450 nm =violet450 - 475 nm =blue500 - 575 nm =green575 — 590 nm =yellow590 — 770 nm = red

[NOTE: All electromagnetic radiations are physically the same. However, the optical systemof the eye is such that only the visible range of wavelengths is absorbed by the lens.]

Light sources

Incandescent lights consist of a tungsten filament which is heated in an inert gas. The higherthe temperature, the more light produced. Light from this source tends to be harsh and tendsto highlight the red end of the spectrum.

Fluorescent lights operate by electrical excitation of atoms that produces spectral lines atspecific wavelengths which then impinge onto fluorescent materials which convert theincident light into light at a longer wavelength. Light produced is softer but can producecolour distortion at particular wavelengths.

Natural light is too variable for use in evaluating appearance of foods.

Light - Object interactions

Light incident on an object may be:

• Absorbed;• Reflected;• Transmitted; and• Refracted.

The relationship between and within each of these components is responsible for the colourand gloss characteristics of the food. The main light/object interactions produced are:

Lightness/value;Colour/hue;Chroma/purity; andGloss.

Physical form

The second class of product appearance is physical form that can be subdivided into threeparts:

Sensory Evaluation


• Shape;• Surface texture; and• Visual consistency.

Shape and size are important from a food technologist's point of view because these can bealtered during the manufacture of processed products. Some examples include:

• Sliced, diced, pieces whole• Length of frozen French fries• Cut of beans• Extrusions

Surface texture can indicate product texture. Some examples include:

• Open dry structure of meat• Wrinkling of peas• Wilting of lettuce

Visual consistency can indicate product viscosity as in:

• Setting of a jelly• Syrups of different concentrations• Pastes and purees

Mode of presentation

This aspect should be considered from a marketing point of view and is important because itinfluences sales. Mode of presentation is applicable on the supermarket shelf (at retail level)and also in terms of presentation at the table (home and restaurant).

Factors to be considered are:

• Product description - name, price, ingredient, etc;• Packaging - shape, design, colour;• Contrast - phenomena of adjacent colours; and• Illumination - affects apparent product colour.

Sensory Evaluation


Summary

Appearance is an important aspect of food quality as it is the first subjective evaluation madeof food quality. The product has to pass the visual assessment before the consumer can orwill consider the other parameters such as taste and texture.

Factors that should be considered in evaluating product appearance include:

• use of standard conditions:• light source (type, intensity, colour);• background; and• style of presentation (unless tested).• selection of appearance attribute(s) for inclusion on scoresheet;• using appearance to reduce tasting load;• should be masked to eliminate unwanted interactions when assessing parameters

involving other senses; and• colour charts/standards help rating.

Sensory Evaluation


THE SENSE OF SMELL(Odour/olfaction)

Stimuli = volatile chemicalsReceptors= olfactory cells in the nosePerception=smell, odour, aroma, flavour

Smell is one of our most primate senses. Supposedly prehistoric people were moreinfluenced by smell than other senses.

The human nose is capable of detecting thousands of different odour substances. However,our sensitivity is much less than other animals. (Animals use smell - food, mating, territoryetc).

Smell is detected both before and during eating. Smell is an important aspect of flavour.There are 20x106 olfactory receptors, but only about 1000 taste receptors.

Odour description requires the development of an odour/flavour memory, e.g. fishy, flowery,woody. This is the basis of flavour/odour memory development by wine judges andmilk/cheese graders. Individuals vary a great deal in their sensitivity to differentodours/aromas.

Anatomy of olfactory system

From the diagram it can be seen that most of air misses the olfactory area. Only 5-10% ofinspired air passes over olfactory receptors. However, this amount can be increased bysniffing harder; obviously the more air which passes over the receptors the better the

Sensory Evaluation


response.

The large number of olfactory receptors (20x106) enable detection of :

• More odours than tastes;• A greater variety of odours; and• Odours at much lower concentration (10 molecules/mL).

In order for odour to register:

• Substance needs to be volatile enough to get into air in the sensory region.• Substance needs to be partially soluble in mucus covering of receptors.• Minimum number of odorous molecules need to be present.• Need to be in contact with receptors for minimum time.

Olfactory intensity

Human nose is about 10-100 times more sensitive to odours than any physico-chemicalanalysis (e.g. gas chromatography). It has been demonstrated that human nose is capable ofdetecting ethyl mercaptan at a concentration of 0.01 mg/230m3 of air, which is equivalent toabout 8 molecules/receptor.

Olfactory threshold

Detection threshold is the concentration where smell is detected.Recognition threshold is the concentration where the smell is recognised.

Olfactory interactions

Nature of the response may change with concentration (e.g. perfumes at low concentrationare pleasant but at strong concentration may be unpleasant).

Interaction of odours:• Additive - increase intensity;• Suppressive - decrease intensity; and• Blending - when new odour unrelated to originals.

Olfactory adaptation

Initial sensation maybe strong - but weakens and makes identification difficult; this is due toadaptation of olfactory receptors.

In testing we therefore need to allow for this by:• Taking first impression of odour and/or• Waiting between tests to allow receptors to recover.

Sensory Evaluation


Summary

• Smell is a major component of food flavour.

• Human nose is much more sensitive than analytical instruments.

• Foods contain numerous compounds of varying volatility that can make analyticalinterpretation difficult (e.g. strong peaks may produce weak odour whereas weakpeaks may produce a strong odour).

• Smell measures perception of a mixture; analytical testing does not.

THE SENSE OF TASTE(Gustation)

Stimuli = soluble chemicals or chemicals which are solublised during chewingReceptors= taste buds in mouthPerception=taste, flavour

What is commonly referred to as taste/flavour is actually a combination of:

• Taste;• Smell;• Touch; and• Temperature.

Strictly speaking taste involves only those sensations mediated by the Gustatory Nerve Fibresand these sensations have five (5) basic qualities:

• Salt;• Sweet;• Sour; and• Bitter.• Umami

Taste stimuli

Taste response requires an aqueous solution of the substance (stimulus) to contact the tastebuds. Therefore, saliva secretions are important in terms of ensuring contact between theproduct and the taste buds. Saliva production is generally stimulated by chewing, as well asthe appearance and odour of the food. The tongue is important as it brings the food intocontact with the taste buds and also provides a mixing action which enables an evendistribution of food about the taste buds as well as preventing the development ofconcentration gradients.

Sensory Evaluation


Taste receptors

The receptors for taste are the taste buds and these are mounted on papillae (folds in the skinof the tongue). The area of greatest response is the top of the tongue. Other areas in themouth and throat where taste buds are situated include: palate, pharynx, larynx, tonsils,epiglottis, lips, cheeks, underside of tongue and floor of mouth.

Taste buds are mainly located at the tip, sides and rear of tongue. There is very little responsein the centre of the tongue. Different areas of the tongue are most responsive to differentsensations.

• Tip sweet• Sides - salty• Sides - sour• Rear - bitter

Taste cells constantly degenerate and regenerate. Their life cycle is 10 days and they areeasily destroyed by heat.

The tongue itself is important as it brings the food into contact with the taste buds and alsoprovides a mixing action which enables an even distribution of food about the taste buds aswell as preventing the development of concentration gradients.

Sensory Evaluation


The five basic tastes

A basic taste is one for which specific taste buds have been identified as beingphysiologically responsible for the particular taste sensation.

Sourness

This is the simplest taste as only acids (H+) produce sourness and as the (H+) increases thesourness increases

However there are some anomalies to this:

• organic acids are more acidic than expected.• sourness of aliphatic organic acids relates to chain length.• some amino acids are sweet (aspartane)• picric acid is bitter• sugar may enhance/depress sourness• sourness is also affected by pH and acid• presence of buffers affects sourness

Sweetness

The common substances that produce the sweet taste are the sugars and other hydroxycompounds such as alcohols and glycols. Other substances such as lead salts, amino acids,proteins, non-nutritive sweeteners (cyclamates, saccharin and aspartame ) also taste sweet.

Saltiness

Many crystalline water-soluble salts yield a salty taste, but only sodium chloride gives a puresalty taste. Other substances taste salty but also bitter, alkaline, sweet and salt in variouscombinations.

Bitterness

Many chemically different compounds have a bitter taste. However, bitterness is mainlyassociated with alkaloids such as caffeine, quinine, strychnine and nicotine. Originally it wasthought that bitterness was an indication of danger (poison). However, many alkaloids areused as drugs (e.g. codeine) and many other bitter substances are harmless (glycosides, estersand aldehydes and tannins in wines and tea).

Bitterness is generally perceived at very low concentration and a relationship appears to existbetween sweet and bitter as many sweet substances produce a bitter aftertaste (saccharin).Bitterness is the taste which most people have difficulty in detecting and response level variesgreatly from individual to individual.

Sensory Evaluation


Umami

Umami is the taste that has been shown to be associated with substances that containglutamate. The most notable example is mono-sodium glutamate (MSG). MSG is wellknown as a flavour enhancer and can cause adverse reactions in some sensitive individuals.However, there are many other compounds which contain glutamate and which are capable ofproducing the savoury, spicy, brothy taste associated with MSG. Many foods containnaturally high levels of glutamate.

Taste interactions

Having described the 5 basic tastes it is obvious that foods are a very complex system whichcontain many different taste compounds and therefore many different tastes. The fact thatthere are only 5 basic tastes and yet we are able to detect hundreds of different tastesensations is due to a series of complex taste interactions that can range from simple 2 wayinteractions to complex 5 way interactions

Interactions between the 4 basic tastes were previously described simplistically by the tastetetrahedron.

Adaptation and fatigue

During exposure to a stimulus, sensitivity decreases due to adaptation and fatigue. This lossin sensitivity varies considerably with the taste (sweet, sour, salty or bitter) and also with thecompound. For example, tasting a series of acids causes the sensitivity to be reduced by thepreceding acids. However, recovery is usually rapid because most common organic acids arevery soluble.

Taste thresholds and sensitivity

There is great variability between individuals in their levels of sensitivity. Sensitivity isaffected by:

• Temperature;• Sleep;• Hunger;• Age; and• Sex.

Absolute/Detection threshold - Concentration of stimulus at which a subject can detect adifference between two samples in a paired test.

Recognition threshold - Concentration at which the specific taste can be identified.Recognition threshold is generally higher than detection threshold.

Both absolute threshold and recognition threshold will vary between individuals. Mostpeople can detect taste within 0.2 - 0.6 seconds and therefore if there is no response withinthis time the level is sub-threshold. However, recognition times vary between the basic tastes

Sensory Evaluation


• Salt = 0.3s• Sweet = 0.4s• Sour = 0.5s• Bitter = 1.0s• Vision = 0.02s• Hearing = 0.01s• Touch = 0.005s

Reaction times also relate to retention times for example; bitterness has the longest reactiontime (1.0s) and the sensation lingers considerably after tasting.

Summary

• ·Five types of taste receptors - salt, sweet, sour, bitter and umami.

• ·Different areas of the tongue respond to different sensations.

• ·Substances must be dissolved for taste buds to detect them.

• ·Flavour of the food is a complex interaction of different tastes and odours.

• ·Sensitivity to taste varies between individuals and is affected by their physiologicalstate.

THE SENSE OF HEARING(Audition)

Stimuli = physical movement of sound waves in a medium (air)Receptor= ear drumPerception=sound, hearing

Hearing

Sound is the perception by humans of vibrations in a physical medium (air). The sound offood when it is being eaten is an important aspect in determining quality.

Positive aspects:

• Snap, crackle and pop;• Fizz of champagne or beer;• Crispiness of lettuce or celery; and• Tapping a melon for quality.

Sensory Evaluation


Negative aspects:

noisy environment may distract tasters or mask product sounds.

THE SENSE OF TOUCH(Texture, Kinesthetics)

Stimuli = physical contact between the food and body tissueReceptors= muscles and nerves in mouth and fingersPerception=touch, feel, texture, viscosity

Texture usually relates to solid food while viscosity relates to homogeneous liquid foods andconsistency relates to non-homogeneous liquid foods.

Instrumental methods only measure one aspect of "texture" and again cannot relate thecomplex interactions which produce the perception of food texture.

Finger feel

Firmness/Softness indicates the eating quality of some food products:

• Ripeness level of fruit such as avocado and mango;• Crumb texture of bread;• Firmness of cheese; and• Spreadability of butter or spread.

Juiciness can be used as a subjective quality index (eg the “thumbnail” test for corn).

Mouth feel

Liquids

• Viscosity - thin to viscous, e.g. milk, cream.• Consistency - thin to thick, e.g. fruit yoghurts.

Solids

Classification of textural characteristics - assessed mainly by chewing.

Textural Terminology Mechanical Characteristics

Hardness Soft, firm, hard, e.g. fruit ripeness, cheese maturity.

Brittleness Crumbly, crunchy, brittle, e.g. muesli bars and biscuits

Chewiness Tender, chewy, tough, e.g. meat.

Grittiness Gritty, grainy, coarse, e.g. stone cells in fruit, "sand" inice-cream.

Sensory Evaluation


Fibrousness Fibrous, cellular, e.g. string/fibre in vegetables.

Moistness Dry, moist, wet, e.g. cracker biscuit, cheeses, watermelon.

Oiliness/Greasiness Oily, greasy, fatty, e.g. french fries, chips.

SENSORY INTERACTION

As has been indicated previously when eating or tasting food there is a continuousrelationship between the senses and unless steps are taken to separate the individual senses orstimuli, interactions may occur. It is not known whether interactions occur at the receptorsite or the brain. However, the second option would appear to be more likely.

Interaction between senses

This is the ability of a response from one modality to influence or affect the response fromanother. There are two aspects of this:

Positive - interactions giving clues to possible identity, e.g. pink milkshake being strawberryflavoured.

Negative - If clues are not correct this may lead to confusion and a wrong judgement, e.g.pink milkshake with pineapple flavour.

Types of sensory interactions

Taste - odour

Receptors for these two senses are very close so that interactions between these senses arehighly likely and these may be important in classifying a particular taste.

Taste - tactile

The taste threshold for sugar, salt, caffeine have all been shown to be lower in water than intomato sauce. This may be due to the fact that in more viscous solutions the chemicals do notreact with the receptors as easily as in pure solutions.

Taste - sight

This is a very important aspect because vision is the first sense affected and appearance of aproduct will have a major influence on absolute quality. Bright colours indicate strongflavours whereas dull colours indicate mild flavours.Other interactions include:

• Odour - Sight• Odour - Tactile• Taste – Hearing

Sensory Evaluation


• Odour - Hearing

Multiple interactions

Multiple interactions between more than two modalities are also possible.

Example: Tasting food pureed, blindfolded and with nose clips gives a different responsethan when interactions are allowed.

Interactions between stimuli

These interactions are more difficult to define and measure but are just as important asinteractions between the senses. Some examples include:

• suppression of one flavour by another, e.g. sweetness is suppressed by acidity. This isthe basis of ensuring brix/acid ratio for fruit juices are constant;

• neutralisation of one flavour by another;

• blending to produce a totally different flavour, e.g. garlic flavoured cheeses;

• partial blending producing a new flavour and the original flavours;

• no effect; original flavours are distinct and separate, e.g. fruit in cheese;

• intensification resulting in enhancement of flavours, e.g. salt and MSG on foodimproves the natural flavours.

Similar situations may exist for all other stimuli.

Summary

Interaction must be considered when designing sensory panels. If only one sense or stimulusis to be evaluated then all others must be masked. However, if interactions are required thenensure this can be achieved by means of sample preparation.

Sensory Evaluation


OPERATIONAL PRINCIPLES OF SENSORY TESTING

When evaluating properties of foods using people as measuring instruments it is important tocontrol the methods and conditions of testing as rigidly as possibly. This helps to eliminatethe numerous errors or biases that can be caused by psychological and physiological factors.

The mental attitude and physical condition of a taster, and the atmosphere of the testingenvironment all influence their judgements. There are therefore a number of basic ruleswhich should always be applied, as stringently as circumstances allow, when running tastepanels. These relate to:

• Selection of panellists;• Preparing the testing environment;• Designing the experiment;• Preparing samples;• Serving samples.

General principles that should always be followed are:

Never ask anyone to taste food they do not like;

Make sure that the "correct" panellists are selected (see section on panel selection andtraining) and that they know in advance when they will be required.

Keep a strict control over all variables except those being tested (e.g. sample size andtemperature).

Make sure the environment gives optimum opportunity for concentration. Tasting properly isa difficult job. Train panellists to be silent while tasting. This prevents panellists frominfluencing one another.

Make tasting interesting and desirable. Use rewards to motivate taters, vary these and choosefoods that contrast with those being tasted. Motivated tasters are more efficient. Givefeedback on results whenever possible.

Avoid giving any unnecessary information to panellists that may influence their scores.Tasters usually find what they expect to find; e.g. in a storage test they expect to find samplesdeteriorating.

Plan your experiment in advance. Which will be the best test to use? Consider all aspectsincluding how you will get the information required from your results (statistics). Runpreliminary tests, i.e. practise and choose the best method for:

Sample size - adequate but not excessive;Serving temperature - standardise for all samples. It must be maintainable, and be anacceptable temperature for the food;Serving vessels;Eating utensils.

Sample preparation and serving

Sensory Evaluation


Serve tasters promptly and make sure they have everything they need.

Run a taste panel as you would expect a good restaurant to be run, i.e. give courteousfriendly service, be efficient, and serve good food.

Keep accurate records of any cooking or preparation methods used. Record temperatures andsize of samples served and any special conditions (e.g. coloured lighting).

It is important that panellists do not see the samples being prepared as this may indicatequality difference.

Sample preparation should be uniform:

• Temperature• Cooking• Thawing• Size and shape (provided this is not a variable)

Sample should be randomly allocated to:

• Avoid bias• Overcome any non—uniformity

Sample size should be adequate:

• 30g solids• 30mL liquids

Samples should be served immediately after preparation to reduce:

• Flavour loss• Discoloration• Textural changes

Sufficient samples should be prepared to allow for seconds

Sensory Evaluation


Containers for presentation

Containers for presentation and tasting should be:

• Clean• Identical for all samples and sessions• Disposable containers or re—usable• Coloured to mask product appearance (if required)• Relevant to product

Serving temperature

• Serve at room temperature where possible• Preference tests use normal temperature• Difference tests may alter temperature to accentuate flavours/odours• Do not overheat:

too hot to taste drying out off flavours browning

Dilutions and Carriers

Most foods should be served in the way they are normally eaten. However, some productssuch as spices, chillies, alcohol, onions, etc. may require dilution before testing. If dilutionsare used they must be uniform in terms of diluent and concentration.

Carriers are substances that are added to assist tasting of certain products. Carriers are aproblem because they can be:

• Expensive• Time consuming• Variable quality• Difficult to control product/carriers ratio uniformity.

For example: developing a cake icing individually may not allow for interaction with flavouror it may be incompatible with the cake (affects texture or falls off).

Number of samples

Samples / Sessions

The number of samples presented at any testing session will depend on:

• Type of product - strong flavour —> less samples• Type of test• Rating scale may require fewer samples• Test dictates sample number eg: triangle test = 3 samples

Sensory Evaluation


• Type of panel — trained / experienced -> more• Experimental design

As a general rule usually not more than 6 samples/sessions.

Sessions / Trials

Before starting your scheduled tasting sessions run two preliminary sessions. These willfamiliarise your panel with the scoresheet, the products to be tested and the procedures youwish them to follow. It also gives you practice at preparing and serving the quantity ofsamples needed, and a last chance to iron out any unforeseen problems.

In calculating the number of sessions consider the following:

• Total number of samples for tasting• Statistical design• Taster fatigue• Motivation• Type of panel (trained/untrained)

Phsiological factors in taste testing

Time of Tests

• Monday and Friday are recognised as being bad days for tasting• Normally taste 1 hour before meals and 1 - 2 hours after• Sometimes this becomes difficult in practice due to:• Unavailability of tasters• Number of sessions

Smoking / Taste Affecting Substances

As indicated earlier, smoking affects sensitivity to flavours —therefore should either:

• Not use smokers• Ensure they do not smoke for at least 1 - 2 hours before tasting• Chewing gum, mints and spices etc may also influence taste

Illness

Sensitivity of people suffering from illness is reduced -particularly those with colds or flu(physical and psychological)

Likes / Dislikes

In preference testing a series of treatments within a specific product type, it is legitimate toeliminate people who dislike the product (or those who are not discriminatory).

Palate Clearing

Sensory Evaluation


It is a good idea to get panellists to cleanse their palate:

• Before tasting to remove any lingering tastes• Between samples to reduce adaptation of taste buds.• Warm water, biscuits, bread, apples may be used as a palate cleaning agent.

Palate clearing can be optional but whatever is done must be constant.The time between samples should also be kept constant if possible

Perfumes / Spices

Ask panellists to refrain from wearing strong perfumes or breathing spicy odours whereverpossible.

Psychological factors

Because sensory evaluation is a subjective system, it is necessary to allow for anypsychological factors that may influence results and possibly lead to errors.Motivation

Good results can only be obtained from a co-operative, responsive panel. Tasting becomes achore when there are large numbers of samples/sessions involved. Motivating panellists bycan reduce this problem by:

• Stressing importance of work• Stimulating company expansion• Greater profits• More pay• Ensuring panellists know what is involved with the trial ie: sessions, products, when

and where tasting will be conducted• Having adequate facilities• Using effective methods and designs• Publicising results obtained from work• Rewarding panellists

Sample Coding

Remove possible bias or influence from samples codes. Do not use.

• Single digit numbers• Consecutive letters• Same codes at consecutive sessions

Randomly or statistically generated three digit number codes are best.

Order of Presentation

Always use either a random order of presentation or a statistically balanced design to avoid:

Sensory Evaluation


• Donkey vote (first is best; last is worst)• Position bias - in triangle tests middle one is different• Contrast effect — good after bad appears better, or bad after good appears worse.

Devise your own system for remembering orders, e.g. 3 digit numbers - put in sequence ofone of digits. Keep it a secret!

Always work systematically in coding, labelling, setting up, e.g. as in reading a page

(1) Left to Right(2) Top to Bottom

This provides an automatic check if something goes wrong.

Balance presentation of samples whenever possible. This avoids contrast effect.

ie. 2 samples A, B. - Half panel taste A first, other half taste B first.- Half panel receive A on the left, other half

receive B on the left.

3 samples 6 different orders in which they are tasted. Useevery order the same number of times. Numberof tasters is a multiple of six.

- Position of samples on plate must also bebalanced.

4 samples 24 different orders: use them all if possible (seetable on next page).

4 samples Generate random order. Write out set of cardsand shuffle them.

When you cannot use balance to eliminate bias, use randomisation.

Sensory Evaluation


Four sample balanced orders

1 A B C D2 A B D C3 A C B D4 A C D B5 A D B C6 A D C B7 B A C D8 B A D C9 B C A D10 B C D A11 B D A C12 B D C A13 C A B D14 C A D B15 C B A D16 C B D A17 C D A B18 C D B A19 D A B C20 D A C B21 D B A C22 D B C A23 D C A B24 D C B A

Expectation Error

Any information a panellist receives before a test will influence the results. This is calledexpectation error. To overcome this:

• Do not give detailed information about treatments• Do not use people on panel who know what the treatments are• Sample coding and design can prevent expectation error

Logical / Stimulus Error

Tasters look for clues to get the “right” answer eg: a difference in sweetness may beassociated with sample differences such as size, shape and colour. This error can beovercome by ensuring sample preparation is uniform or use masking.

Halo Effect

When more than one factor in a sample is evaluated at one time the result obtained may bedifferent than if factors evaluated separately. This can be overcome by tasting each aspectseparately. However, this is time consuming and would only be done if extremely accurateresults were required. Testing one aspect at a time in preference does not simulate the “real

Sensory Evaluation


situation” ie: consumers do not taste every aspect separately.

Suggestion

Influence of other panellist may bias or influence results. This can be prevented by:

• Using booths• Not allowing talking in tasting area• Reducing outside distractions

Questionnaire design

Questionnaire design should be simple and easy to follow in terms of design and languageand make sure tasters know how to use it. You may need to include some instructions on thescoresheet itself, but it is usually better to give instructions verbally to your panel first. Thequestionnaire should generally not be more than one page and include:

• Name• Date• Time• Product• Sample codes• Instructions• Comments section

Sensory Evaluation


DESIGN OF A SENSORY TESTING AREA

The main considerations to keep in mind when preparing an area for sensory testing concernthe requirements for an atmosphere conducive to concentration, where conditions can becontrolled. Sensory panellists need somewhere comfortable and free from distractions if theyare to be able to "tune in" to the sensations triggered by the stimuli in the food products theyare tasting. Product characteristics can be markedly affected by temperature and humidity,and appearance is affected by lighting intensity.

The conditions should be controlled in order to :• Reduce bias• Improve accuracy• Improve sensitivity• (compare to the conditions used in an analytical laboratory)

International standard (ISO 8589-1988)

The standard looks at the design of the testing area for both new and existing buildings. Italso specifies which recommendations are considered essential and which are only desirable.Important points summarised from the standard are listed below. If designing an area that isto be dedicated solely to taste panel work, these should be seriously considered.

Total area should include:

• Testing area with individual booths and a group area;• Preparation area/kitchen;• Office;• Cloakroom;• Rest room; and• Toilets.

General testing area

• Easily accessible but in quiet position.

• Location - close proximity to preparation area, but separate entrance, and withcomplete "close-off" capability.

• Temperature and relative humidity - constant, controllable, and comfortable.

• Noise - keep to a minimum, soundproof area as much as possible.

• Odours - keep area free from odours (air conditioner with carbon filters, slightpositive pressure).

• Use odourless materials in construction and decoration.

• Use odourless cleaning agents.

Sensory Evaluation


• Decoration - use neutral, light colours for walls and furniture (e.g. off-white, lightgrey).

• Lighting - ambient lighting must be uniform, shadow-free and controllable. Forconsumer testing - as close to home conditions as possible.

Booths

Number - minimum three, normally five to ten - six is a useful number since it fits in wellwith balanced ordering of 3 samples.

Space - allow sufficient space for movement of tasters and for serving samples.

Set-up - permanent booths recommended. Temporary acceptable. If adjacent to preparationarea include openings in the wall to pass samples through. Size and style specified. Considerspace for samples, utensils, spittoons, rinsing agents, scoresheets and pens, computerisedequipment. Include comfortable seats.

Lighting - uniform, shadow-free, controllable, adequate intensity for assessing appearance.Devices to mask appearance (e.g. dimmers, coloured lights or filters).

Group work area

General Necessary for discussion and training purposes. Include large table andseveral chairs. "Lazy Susan" useful. Include board for discussion notes, etc.

Lighting As for general area, with coloured lighting options like booths.

Preparation area

General Located close to assessment areas but no access to tasters. Design for efficientwork-flow. Well ventilated. Flexible services (i.e. plumbing, gas, electricity).

Equipment Depending on testing required. Include working surfaces, sinks, cookingequipment, refrigerator, freezer, dishwasher, etc. Storage space for crockery etc. Crockery,glassware etc for serving samples.

Office area

General Separate but close to testing area, reasonable size, desk, filing cabinet,computer, bookcase. Photocopying service needed.

Additional areas

Useful to include rest room, cloak room and toilets.

Practical alternatives

The requirements specified in the International Standard (ISO 8589) will obviously provide asuitable area, but they are not always feasible, either from the point of view of financial

Sensory Evaluation


resources or physical space available.

Very few industries are able to start from scratch, designing new premises solely dedicated tosensory analysis work. I therefore would like to abbreviate the list proposed in the standardto one which I consider includes the bare essentials.

Minimum of 2 areas:

Preparation area and office area. If possible position these at opposite ends of the room toavoid messy paperwork!

Testing area with entrance separate from preparation area.

Preparation area requires

• Adequate storage for utensils and equipment;• Adequate working surfaces to set out samples;• Washing up facilities - minimum double sink with hot and cold running water;• Refrigerator - minimum 2 door with separate freezer, preferably at least auto-defrost;• Cooking equipment - depending on sample requirements;• Rubbish bin - large with liner bags;• Source of boiling water;• Hand washing facilities.

Testing area requires

• Comfortable chairs for panellists;• Minimum space - 4 panellists;• Table which can be easily divided into booths if required;• All equipment likely to be needed while a panellist is tasting, e.g. pencils, spittoons,

toothpicks, tissues/serviettes;• Well placed, efficient lighting;• Waiting are with noticeboard - for tasters to wait for booths to become free and to

collect rewards after tasting.

A system using collapsible booths can work quite well if it is not possible to keep an areasolely for sensory work. These may be made of painted wood, heavy duty cardboard, or"corflute". They can be made specifically to fit any available benches or tables and foldedand stored when not in use.

The type of facility will depend on:

• Finance• Available space• Frequency of use• Tests conducted

Sensory Evaluation


STATISTICAL PRINCIPLES

This section looks at the role of statistics in sensory evaluation and introduces some termsand concepts required to correctly apply statistical methods in evaluating sensory type data.

Why do we need statistics in sensory evaluation?

When we measure something (eg salt level in cheese) we find there is variation in what weare measuring. This variation is called natural variation or experimental error and impliesthat there is some true measurement but because of our limitations we cannot reproduce thecorrect readings every time. This is a fact of life and we have limited control over this sort oferror.

Because of this variation there is some risk in making decisions about changing formulationsor introducing new products onto the market. Using statistics we have rules to estimate andminimise the risk and enable us to extrapolate our results from an experiment to a moregeneral situation.

What is an experiment?

It is any process that generates raw data.

There are many sources of error in sensory data. Some of these include.

• differences between people, (likes and dislikes)• differences within a person from time to time, eg adaptation• differences among samples,• differences in interpretations of scales• and many more.

How can we describe our data?

Lets say we have collected some data from an experiment and we have 20 scores of flavouracceptability in a mango sample rated on a 9 point hedonic scale. If we plot a bar graph(histogram) using the score along the horizontal axis and the count for a particular score onthe vertical axis then we have a frequency distribution. An example is shown below.

Sensory Evaluation


Looking at the graph or distribution we ask what is the best single estimate of the panelsscore and what is a good measure of their variability? The best or most likely singleestimates are called measures of central tendency. The three most commonly used are:

mean - or average (sum of all data values divided by number of observations)median - 50th percentile or middle valuemode - most frequent value, good for categorical data

Measures of variability include the range, standard deviation and variance. The range issimply the difference between the smallest and the largest. The standard deviation isprobably the most common and is calculated by using the formula below.

sX M

N=

−

−∑ ( )

( )

2

1

where M is the mean or average of X scores and N is the number of scores. This formulacalculates the deviation of each score from the mean and squares it to take into accountpositive and negative values and the square root is then taken to bring it back to the originalunits. The variance is simply the square of the standard deviation and is used in a number ofstatistical formulas.

0

1

2

3

4

5

6

3 4 5 6 7 8 9

Flavour Acceptability

Freq

uenc

y

Sensory Evaluation


The normal distribution

Many things we measure about a group of people will be normally distributed. This meansthey will form a bell shaped curve described by an equation usually attributed to Gauss.

How does the standard deviation relate to the normal distribution?

Standard deviations describe discrete percentages of observations at certain degrees ofdifference from the mean. So for a normal distribution about 66% of our data will be withinone standard deviation of the mean and about 95% will be within two standard deviations.For our mango flavour data with a mean of 6.0 and standard deviation of 1.89 then 66% ofour data lie between 4.11 and 7.89. If the standard deviation had been 1.00 then 66% of thevalues would be between 5.0 and 7.0, a smaller range indicating less variability.

In addition any score, X can be described in terms of a z-value, which describes how far thescore is from the mean in standard deviation units.

Z = X-µ/σ

Since z-scores are related to percentages under the normal curve they can predict how far ascore is from the mean and how likely or unlikely it is. So the z-score can be converted to aprobability value or p – value. This p - value is found from the area under the curve outsidethe z score and is the chance with which we would see a score of that size or greater. Tablesare often used to convert z - scores to p – values.

An important concept

When we do an experiment we are using results from a sample taken from a largerpopulation of possible results. Since we cannot take all possible results from the populationwe infer from our sample results what should happen in the rest of the population. Bymaking this generalisation we often express our results in terms of probability or p- values.This is our safety margin or level of confidence about our result. It is often quoted like this -the flavour score for naturally ripened mango was significantly higher (P<0.05) than that forartificially ripened mango.

But what does this mean?

We are at least 95% certain that based on our experimental conditions the naturally ripenedmango will have more flavour than artificially ripened mangoes. This conclusion will bewrong about five times out of 100. Sometimes a 1 % value or 0.01 is used for greaterprecision.

How does all this help?

We need to identify some more concepts before we can be confident in using statistics.Experiments need to be planned and carried out correctly before we can use statistics and twoimportant principles are replication and randomisation.

Replication is the assessment of each treatment more than once. A treatment can be theaddition of sweetener to a product or the storage temperature of a fruit. With replication we

Sensory Evaluation


can assess the natural variability and separate this from our variability due to treatmentdifferences. This is like a signal to noise ratio. Is our signal greater than the backgroundnoise (natural variation)?

Random allocation of treatments to samples or products ensures each sample has an equalopportunity of receiving any treatment, and that this chance is unaffected by the treatmentsassigned to other samples. For example if two products are tasted by 24 tasters and they alltaste product A first then this may well bias the results, as the first product tasted may tend tobe preferred regardless of which it is. Subjective allocation of treatments in a haphazard wayis not a satisfactory alternative to randomisation.

Sensory Evaluation


SENSORY EVALUATION METHODS

There are two main types of sensory methods:

Affective :tests which involve consumer preference or acceptance

Analytical : tests which are involved with analyzing specific product attributes in terms of:

• discrimination/difference• description

AFFECTIVE TESTS

Preference infers a preference for one product over another; either overall or in relation to aparticular parameter.

Acceptance infers actual utilisation/purchase of the product.

Panel selection

Select panel on basis of end use:• Age• Race• Religion• Sex or• Random selection for overall

Panel training

No need for training, in terms of technique or ability. However, panellists should beinstructed/briefed in terms of:

• Method• Questionnaire• Length of trial• Number of samples

Panel size

1. 20 to 100 people2. 20 = pilot consumer panel3. 100 = consumer panel

Sensory Evaluation


SPECIFIC TEST METHODS

PAIRED PREFERENCE TEST(Reference: AS 2542.2.1; 1982.)

Application: to establish whether there is a preference between two samples.

Principle: a pair of samples (one may be a control) is presented to each assessor. Theassessors are asked to choose the sample they prefer.

This test is a ‘forced choice’ ie: the assessors must select one sample as being morepreferable. Responses indicating no preference are not permitted.

Statistically based on null hypothesis that there is no preference between the samples.

ie:PA = PB = 50%= 0 5

Bilateral Test - no expectation of preferences

Specimen Answer form for bilateral paired preference test

Conclusions

• no preference• A preferred to B• B preferred to A

Question — which of the two samples do you prefer? Count the number of replies citing oneof the two samples the more frequently.Conclude that this sample is significantly preferred to the other if the number obtained isgreater than or equal to that shown in Table 4.

Example:

Two drinks ‘A’ and ‘B’, are offered to a panel of 30 assessors. The two samples arepresented under random number eg: ‘789’ and ‘379’. The test supervisor accepts a 5% level

PRODUCT………………….DATE…………..TIME………ASSESSOR…………………..Which sample do you prefer?Please examine code 349 first.Please tick the appropriate box.

Code 922 349Place tick

YOU MUST MAKE A CHOICE

Sensory Evaluation


of significance (ie: P < 0.05%). It is not known which of the two samples contains moresugar.

Question - Which sample do you prefer?Replies: 22 prefer ‘A’8 prefer ‘B’

From Table 4 it can be concluded that Drink ‘A’ is preferred to Drink ‘B’.

Unilateral Test - expect one sample to be preferred.

Specimen Answer form for unilateral paired preference test

Conclusion

• no preference• the declared sample is preferred

Question — Do you prefer sample ‘A’ to sample ‘B’? Conclude sample A is preferred ifnumber of positive replies is greater or equal to the number shown in Table 3.

Example:

Two drinks, ‘A’ and ‘B’, are offered to a panel of 30 assessors. The two samples arepresented under a random number eg: ‘789’ and ‘379’. The test supervisor accepts a 1%level of significance (ie: P < 0.01%). It is known that drink ‘A’ contains more sugar thandrink ‘B’.

Question - Do you prefer sample ‘A’ to sample ‘B’?

Replies: 23 Yes and 7 No.

From Table 3 it can be concluded that there is preference for drink ‘A’ over drink ‘B’.

PRODUCT………………….DATE…………..TIME………ASSESSOR…………………..Do you prefer sample 186 to sample 592?Please examine code 592 first.Please tick the appropriate box.

YES NO


Sensory Evaluation


N.B. If uncertain always use the bilateral test.

Advantages

• Simple test to conduct• Suitable for children and consumer panels• Easy to analyse (for > 100 assessors use t test or CHI squared)

Disadvantages

• Only suitable for 2 products (note – multiple Comparisons can be used but otherpreferences tests are more commonly used. See ASTM manual on sensory testingmethod, STP 434; 1968)

• No magnitude of preference is given ie they both may be disliked but one can still bepreferred.

Applications

• Product Development• Product Matching• Process Change

RANKING FOR PREFERENCE(Australian Standard 2542.2.6)

Principle:

Judges are asked to rank two or more samples in order or preference ie: most preferredsample is ranked first.

Ranking is a forced choice procedure ie no ties are allowed.

Specimen Answer form for ranking for preference.

PRODUCT………………….DATE…………..TIME………ASSESSOR…………………..Please taste the samples in the order presented, moving from left to right and rankthem in order of preference. You may retaste the samples to check the ranking.Give the sample that you most prefer the a rank of 1 and the sample you prefernext a rank of 2 etc.

You must give each sample a different rank. Equal ranks are not allowed.

SamplesRank

Sensory Evaluation


Statistical analysis

Kramer’s tables, which have been used in the past to analyses differences between rank sums,should not be used due to questions of accuracy and statistical validity.

When there is no expectation of a specific rank order being made (eg when rankingpreference of new product prototypes) the Friedman Test should be used (see statisticalmethod s section for details).

Example

Twelve households were presented with four samples of meat seasoning to be used incooking. They were asked to use the samples as directed and to rank them in order ofpreference. The results are shown below:

Sensory Evaluation


Rankings for the preference of four meat seasonings

SeasoningHOUSHOLDA B C D

1 1 3 2 42 2 1 3 43 1 4 2 34 1 4 2 35 2 3 1 46 3 4 2 17 3 4 2 18 3 4 1 29 1 2 3 410 1 2 3 411 1 2 3 412 1 3 2 4Rank sums 20 36 26 38

The F value is calculated as follows:

)14(123)38263620()14(412

12 2222 +×−++++×

=F

=190.8-180 =10.8

the calculated value is compared to the critical f value in table 7 (7.81 for 3 df). since 10.8 isgreater than 7.81, the experimenter can conclude that there is a significant (p<0.05) differencebetween the rank sums.

Two samples will be significantly different if the absolute value of the difference between therank sums is greater than or equal to the following critical value:

6)14(412960.1 +× = 12.396

Sample A B C DRank Sum 20a 36b 26ab 38b

Rank sums that do not have a common superscript are significantly different (P<0.05)

Sensory Evaluation


RATING FOR PREFERENCE(Australian Standard 2542.2.30

Principle

Assessors are asked to evaluate one or more samples and indicate the degree of liking for theproduct or some characteristic of the product.

When performing preference testing it is important to include as many panellists as possible.Personal preferences in foods are being measured which are purely subjective, so the variancein the data is large. This makes it more difficult to obtain statistically significant results. Thelarger the panel, the more chance there is of obtaining a significant result. Only untrainedpanellists are used and should be selected at random or from a targeted group related to theproduct.

Pilot consumer panel = 20-25Consumer panel = 100

Types of response scale

Category scale/structured scale

The response scale is divided into categories or boxes.The response scale is usually divided into an arbitrary number of categories - usually between7 and 13Category scales must be bipolar.Verbal descriptors or facial expressions may be used to identify the levels of acceptance.

Hedonic category rating

AROMA FLAVOUR TEXTURELike extremelyLike very muchLike moderatelyLike slightlyNeither like nor dislikeDislike slightlyDislike moderatelyDislike very muchDislike extremely

Sensory Evaluation


Facial hedonic scale

7 point facial hedonic scale

AppearanceAromaFlavourMouth-feel

Graphic rating scale

• The response is recorded by marking a position on a line• Also called visual-analogue scale, line mark scale or unstructured scale• -Physical lengths 100-150 mm.• This scale may also use facial expressions for measurement.• Numbers and/or descriptors are usually attached to a rating scale.

Recording and interpretation of results

Ratings must be converted to numerical scores for analysis and interpretation. For categoryscales, successive integers are assigned to successive categories and these are used inanalysis, e.g. with a 9-point scale, the integers 1-9 would be used. For graphic scales, thedistance, e.g. in mm, between the response mark and one end of the scale serves as theresponse score.

The arithmetic mean and standard deviation, when obtained for each sample, serve asmeasures of central tendency and variability, respectively. For statistical analysis, theanalysis of variance technique is appropriate (or a t-test in the case of one or two samples).

Correlation or regression analysis may be used for subjective/objective correlations.

Advantages

• Test is relatively simple and easily understood;• Indicates the degree of preference;• Can be used to infer acceptance;• Suitable for different age groups; and• Can measure > one parameter at a time.

Disadvantages

• Statistical analysis is required; and• Results may be biased by type of assessors used.

Sensory Evaluation


Applications

• storage trials• product development• consumer testing• quality control• subjective/objective correlations• research

Example:

Three samples of frozen chicken casserole were presented to a 24 member panel whoassessed the appearance, flavour, texture and general acceptability of the products using a 13point

The following results were obtained:

CHICKEN CASEROLEA B C

Appearance 10.8 a 8.5 d 10.3 bFlavour 9.9a 9.4 b 9.2 bTexture 10.4 a 9.6 b 9.1 bGeneral Acceptability 10.3 a 9.2 b 9.4 b

Scores within each row that do not have a suffix in common are significantly different.

SENSORY EVALUATION IN CONSUMER TESTING

Introduction

The personal response by current or potential customers of a product, a product concept, orspecific characteristics of a product is collectively grouped under what we call consumertesting. However, it is important to define the terms acceptance and preference oftenassociated with consumer testing. Acceptance refers to the degree of liking or disliking for aparticular product or the ability of the product to meet expectations of consumers whilepreference refers to a choice made by panellists among several products on the basis ofliking or disliking. Unfortunately ‘preference’ is widely used as a generic term to describeboth acceptance and preference judgements. It is important to note for example in pairedpreference testing that although one product may be preferred to another, neither product maybe liked to any degree. The term ‘hedonic’ is an adjective associated with degrees ofpleasure or displeasure and is applied to both acceptance and preference testing.

Sensory Evaluation


Applications of Consumer Testing

The reasons for conducting consumer tests usually fall into one of the following categories:

• Product maintenance• Product improvement/optimization• Development of new products• Assessment of market potential

Product maintenance

Research and development projects may involve cost reduction, substitution of ingredients,process and formulation changes and packaging modifications without affecting the productcharacteristics and overall acceptance. Usually difference tests would be used to determinewhether a difference was perceived or not but it is necessary to take the product out to theconsumer to determine if the reformulated product will achieve at least parity with the currentproduct.

Product maintenance is also a key issue with quality control/quality assurance and shelf-life/storage projects. Feedback on consumer response gives important information on thosesensory characteristics that are most important to consumer choice and which shouldtherefore be rigorously controlled. A combination of in-house profile testing on themagnitude and type of change over time, condition, production site, raw material sources etccan be used in conjunction with consumer testing to determine how large a difference issufficient to change the acceptance rating.

Product improvement/optimisation

The intense competition among consumer products drives companies to constantly improveand optimise products so that they can deliver what the consumer is really looking for andtherefore increase market share.

In product improvement, prototypes are made, tested by a trained panel to verify that thedesired attribute differences are perceptible, and then tested with consumers to determine thedegree of perceived product improvement and its effect on overall acceptance or preferencescores.

For product optimisation, ingredients or process variables are manipulated and a trained panelidentifies the key sensory attributes affected and consumer tests are conducted to determine ifconsumers perceive the change in attributes and if such modifications improve the overallacceptability.

Development of new products

During the new product development from concept to a range of trial samples to a modifiedsample range and finally a choice to launch, consumer testing should be used throughout inconjunction with trained panel assessment.

Sensory Evaluation


Assessment of market potential

In addition to the use of sensory evaluation to gather information about key attributes of aproduct, typical marketing questions such as intent to purchase, purchase price, currentpurchase habits, consumer food habits, effects of packaging, advertising and convenience arecritical for the acceptance of branded products. It is often convenient for these marketingtype questions to be included in a questionnaire presented to consumers when assessing thesensory characteristics of the product.

Conducting Consumer Tests

There are a number of factors to consider when conducting consumer tests and these are:

• Test design• Test subjects• Test location• Test questionnaire

Test Design

There are two main types of design, one is qualitative measuring subjective responses whilethe other is quantitative determining the responses of a large group to a set of questionsregarding preference, liking, sensory properties etc.

Qualitative Tests include focus groups, focus panels and one-on-one interviews. Each ofthese has their use in a particular situation depending on what is required and how sensitivethe topic is. Essentially small groups are used to uncover as much specific information fromas many participants as possible. It is frequently recorded either by video and or audio and asummary is made.

Quantitative Tests

Essentially all the good practice principles used in sensory evaluation as described in thedifference and descriptive testing should be followed here such as 3 digit random codes forproduct and presentation in a balanced order. Some typical designs used include:

• Monadic test where only one product is assessed which makes it fast and the leastexpensive but is relatively insensitive and requires large numbers of consumers (atleast 200).

• Sequential monadic where one product is assessed, removed and then replaced by asecond product in a balanced design giving it greater sensitivity.

• Paired preference testing where two products are assessed simultaneously and adirect comparison is made making it quite sensitive.

• Acceptability testing. Usually the nine-point hedonic scale is used to determineconsumers liking of a product and if required the relative ratings for liking can beused as a measure of preference.

Sensory Evaluation


Example of nine-point hedonic category rating

AROMA FLAVOUR TEXTURELike extremelyLike very muchLike moderatelyLike slightlyNeither like nor dislikeDislike slightlyDislike moderatelyDislike very muchDislike extremely

Example of seven point facial hedonic scale often used for children

Graphic rating scale - the response is recorded by marking a position on a line (also calledvisual-analogue scale, line mark scale or unstructured scale) - physical lengths 100-150 mm.This scale may also use facial expressions for measurement.

• Attribute testing can be used to gain information on the reasons underlying overallpreferences and usually category or line scales are used. These can be hedonic typeattributes or sensory attributes in the form of just right scales as shown below.

not sweet enough just right too sweet

Test Subjects

If information on the acceptance of the product by consumers is required, then it is they whoshould do the tasting. However, this is not always practical in preliminary testing of products, soa compromise can be made by using large numbers staff who assess fairly infrequently.However, it should always be remembered that this is a compromise, and results are best

Appearance

Aroma

Flavour

Mouth-feel

Sensory Evaluation


interpreted only in relative, not absolute, terms. Staff cannot be considered to be arepresentative sample of the target population.

When performing consumer testing it is important to include as many panellists as possible.Personal preferences in foods are being measured which are purely subjective, so the variancein the data is large. This makes it more difficult to obtain statistically significant results. Thelarger the panel, the more chance there is of obtaining a significant result.

Recruitment

The number of consumers to be tested depends on the purpose of the test, the test design andthe precision with which the target population can be identified. In general we require 60 to120 for most consumer testing. Recruitment and selection of consumers rely on severalcriteria or demographics such as:

• Product usage. It is important to determine if you are looking for low, medium orhigh users of the product. For speciality products or niche markets, the cost ofconsumer testing increases as more people must be contacted before the requirednumber are found.

• Gender. It is not always necessary to get equal numbers as purchasing or usagehabits vary between products. Researchers should use current market information.

• Age. If a product has broad age appeal then consumers should be selected by age inproportion to their representation in the user population.

• Nationality. Products targeted towards a specific part of the community or for exportideally should be tested in that environment. However, it is possible to use foreignnationals resident here but it depends on how long they have been residing in theiradopted country as they can develop the likes and dislikes characteristic of theadopted country.

• Social class. This can be based on income or occupation although sometimes it isdifficult to get consumers to reveal such information.

• Others including race, religion, education level, employment, geographiclocation, etc. If any of these are important in defining the target audience then theresearcher should consider them.

Source of Consumers

As mentioned it is important to sample properly from the consuming population but becauseof cost restraints employees and local residents may be used for things such as productmaintenance. However, for new products or product optimisation or improvement the correctaudience should be selected. These can come from a database of consumers willing to assessproducts, telephone survey, leaflet drop, shopping centres, embassies, colleges or door todoor.

Test Location

It is possible to conduct consumer testing in a number of locations depending on theresources and the results can vary greatly. Locations include:

• Company laboratory facilities, which give good control of the environment andrapid feedback of results but the sensory booths, are clinical and atypical of a real

Sensory Evaluation


domestic environment.• Central location such as school or church halls or shopping centres are convenient as

large numbers can be tested at one time and on a number of products. However theconditions are artificial compared to normal use at home and the number of questionsthat can be asked may be limited.

• Home use tests represent the ultimate in consumer testing as the product is testedunder its normal conditions of use. In addition to the product itself, a check on thepackaging can also be determined. Generally more information can be gathered as theconsumer gets more time and can perform repeated assessments. However it is timeconsuming and uses a smaller number of people and the possibility of nonresponse isgreat unless consumers are continually reminded.

Test Questionnaire

It is very important that the test questionnaire format is simple, unambiguous, easy to readand understand. You need to consider the objective of the test and any constraints such astime, funding etc. In essence you need to be:

• Brief• Use simple plain English (provide translation for studies involving foreigners)• Be specific• Multiple choice questions should be mutually exclusive• Avoid ambiguity• Watch the effects of wording• Don’t ask what they don’t know• Try and pre-test the questionnaire

For example

How satisfied or dissatisfied were you with the product?

Very satisfiedSlightly satisfiedNeither satisfied nor dissatisfiedSlightly dissatisfiedVery dissatisfied

The product looks like how it is shown on the package.

Agree stronglyAgreeNeither agree nor disagreeDisagreeDisagree strongly

What did you like about the product?This open-ended question allows for the consumer to add something you may have forgottenbut it is sometimes hard to read the answer (handwriting) and some people do not bother withanswering.

Sensory Evaluation


The question order should go from the more general to the more specific and ask overallacceptability first before biasing the consumer with more specific issues. Ask the moresensitive demographic questions last.

Data Analysis

All quantitative data should be subjected to some form of statistical analysis from simplesummary statistics and graphical representation to t-tests and analysis of variance withpairwise comparisons. Further advanced multivariate methods such as principal componentsanalysis and cluster analysis along with regression methods to relate consumer data to otherdata such as linear regression, partial least squares and preference mapping can also be used.

Sensory Evaluation


ANALYTICAL SENSORY TESTS:

In general, analytical panels are used as “measuring instruments and therefore need to be:

• Valid (able to measure appropriate parameters)

• Reproducible

Panellists can be trained or untrained depending on the degree of difference expected.Consumers will not detect the small differences that a trained panel would. An untrainedpanel would require 20-100 panellists while a trained panel would require 5-20.

DIFFERENCE TESTING

Difference tests may be sub-divided into 2 classes:

• Simple difference tests are those that have no direction or characteristic associatedwith the difference between the products. Examples of simple difference tests are:

Triangle test Duo Trio test Two-out-of-five test A not A Difference from control

• Directional difference tests are those that have a direction or characteristic associatedwith the difference between the products. Examples of directional difference testsare:

Paired comparison test Ranking Rating

SIMPLE DIFFERENCE TEST

TRIANGLE TEST

(Australian Standard 2542.2.2 - 1983)

Scope and Application

Used to determine whether a perceptible difference exists between two samples. Thedifference can involve one or several sensory attributes, but no direction or magnitude of thedifference is measured.

The triangle test is an effective method to determine whether a change in ingredient,processing, packaging or storage has resulted in product differences. These situations mayarise in product and process development, product matching, in quality control or as apreliminary test prior to quantitative descriptive testing. A triangle test can also be used for

Sensory Evaluation


the selection and monitoring of panellists.

With products that produce sensory fatigue, carryover effect or adaptation effects, the triangletest has limited application.

Principle

Three samples, two of which are identical, are presented simultaneously to each panellist fortesting in a predetermined order. The panellist is told that two samples are identical and oneis different (odd). The panellist is required to identify the different sample. The triangle testis a forced choice test.

Preparation and Procedure

The samples should be representative of the product and all prepared in exactly the sameway. Select four 3-digit random number codes, two for each product. Prepare scoresheets toprovide equal numbers of the following orders:

AAB BBAABA BABBAA ABB

Make up sets of 3 samples to match the score sheets so that half contain 2 samples of productA and half contain 2 samples of product B (Total number of sets should be a multiple of 6.).Make up sets in multiples of the six arrangements as required for the number of panellists.

If total number of panellists or quantity of products available is insufficient to provide equalnumbers of the 6 orders, you still need to make sure there is a balance between sets with 2‘A’s and 2 ‘B’s. The triangle tests should be presented at random to the panellists. Instructeach panellist to examine in the specified order (e.g. left to right) and remind them that theymust make a decision.

Count the number of correct responses (those that select the odd sample) and compare theresult with those presented in Table 2.

Questionnaire

Specimen answer form for the triangle test

Analysis of results

Product Date Time Assessor

One of the three samples presented is different from the other two.

Please examine in the order requested and place a circle around the code of the samplewhich is different.

293 594 862

You must make a choice

Sensory Evaluation


The total number of correct responses is counted as well as the total number of responses andcompared to the statistical tables (Table 2). This is based on the probability that if there is noreal difference the odd sample will be chosen a third of the time.

Example

A company wishes to put a new dessert topping on the market. The product developmentsection has two different thickening agents available to them, one which is considerablycheaper. They wish to know if there is any difference in the products made using the 2different thickeners.

Two batches (A, B) are prepared using the two different thickening agents and samples arepresented to 17 assessors. As each assessor will only make one assessment, it will benecessary to prepare 27 samples of A and 27 samples of B, and arrange them to provide threeof each of the six possible arrangements as indicated above. One set is discarded and theremaining 17 sets are randomly distributed between the assessors.

The number of correct responses is 10, ie the number of panelists who correctly selected theodd sample from the 3 samples presented.

The test organizer will accept a risk of error of 5% (P<0.05), that the test will reveal adifference when there is none.

Table 2 indicates that for 17 assessors at P<0.05, 10 correct responses are required forsignificance.

It can be concluded that the product from the two thickening agents are significantly different(P<0.05).

What should the test organizer do next???

DUO-TRIO TEST(Australian Standard 2542.2.4 - 1988)


Used to determine whether a difference exists between two samples. The difference caninvolve one or several sensory attributes, but no direction or magnitude of the difference ismeasured. A duo-trio test can be used when one of the products is an existing standard orreference.

A duo-trio test can be applied to determine whether changes in ingredients, processing,packaging or storage have resulted in differences between products. The duo-trio test findsapplication in the selection of panellists, product and process development, product matching,quality control and as a preliminary test prior to analytical descriptive testing.

Statistically the duo-trio test is less powerful than the triangle test because the chance ofguessing a correct result is one in two. The Duo-Trio test is therefore only used when it is

Sensory Evaluation


required to form a judgement. This is the case when tasting a product with a lingering after-taste such as bitterness, spicy or chilli.

Principle

Three samples, two of which are identical, are presented to each panellist. One sample isidentified as the reference sample and panellists are instructed to assess the reference samplefirst and then identify which of the two samples is the same as the reference. It is a forcedchoice test.


The samples prepared should be representative of the product and prepared in exactly thesame way. If possible, samples are presented simultaneously or if required, sequentially.There are two forms of this test: balanced reference mode and constant reference mode.

Balanced reference mode

This is used when both the samples are unfamiliar and so both the samples are used as thereference sample.

Select two 3-digit random codes, one for each product. Prepare scoresheets to provide equalnumbers of the following orders:

RA A B RB B ARA B A RB A B

Make up sets of 3 samples (reference plus two samples) to match the scoresheets so that halfcontain 2 samples of product ‘A’ and half contain 2 samples of product `B'. (Total number ofsets should be a multiple of 4).If total number of panellists or quantity of products available is insufficient to provide equalnumbers of the 4 orders, then you will still need to check that there is a balance between setswith 2 ‘A’s and 2 ‘B’s.

The sample sets are allocated at random to the panellists. Instruct each panellist to assess thereference sample first, followed by the two other samples in order (e.g. left to right). Remindthem that they must make a decision.

Constant reference mode

The constant reference duo-trio test is useful when you have trained panellists. In this test,one of the samples is a familiar product or designated standard. It is therefore the only oneused as a reference sample. The number of possible presentation orders is thus restricted to:

RA A BRA B A

Select two 3-digit random codes, one for each product and prepare the scoresheets so thatequal numbers of the two orders are presented. (Total sets should be a multiple of 2).

Sensory Evaluation


Randomly allocate sample sets to panellists and instruct each panellist to assess the referencesample first, followed by the two other samples in order (e.g. left to right). Remind them thatthey must make a decision.

Analysis of results

Count the number of correct responses as well as the total number of responses and use thestatistical Tables 3.

Questionaire

Example

A duo-trio test was used to determine if methional could be detected when added to cheddarcheese in amounts of 0.125 ppm and 0.250 ppm. Each tray had a control sample marked Rand two coded samples, one with methional added and one with no methional. The duo-triotest was used in preference to the triangle test because less tasting is required to form ajudgment. This fact is important when tasting a substance with a lingering aftertaste, such asmethional.

The test was performed on two successive days using eight judges. Each day the judges werepresented with two trays. One tray contained a sample with 0.125 ppm methional and twocontrol samples and the other contained a sample with 0.250 ppm methional and two controlsamples. A total of 16 judgments were made at each level. The results are shown in thefollowing table.

DUO-TRIO TEST

Name: Date: Time: Product: .

You are provided with three samples. The left-hand one is a reference; one of the other two isthe same as the reference.

Taste the samples in the order left to right and circle the number of the sample which is thesame as the reference.

Reference Sample code:. . . . . . . . . Sample code: . . . . . . . . .


Comments:

Sensory Evaluation


Duo trio test on cheddar cheese containing methional. 0.125 and 0.250 ppm.

Day1 Day 2

JUDGES 0.125 0.250 0.125 0 .250

1 X R R R2 R R R R3 X R X R4 R X X R5 R R R R6 X R X X7 R R R R8 R R R RTOTAL 5 7 5 7

X = wrongR = right0.125 ppm = 10 out of 16 correct judgments0.250 ppm = 14 out of 16 correct judgments

Consult Table 3 for 16 judges in a two sample test. This chart shows that 12 correctjudgments are significant at the 5% level.

The conclusion is that methional added to cheddar cheese can be detected at the 0.250 ppmlevel but not at the 0.125 ppm level. What would you do next??

Advantages

used where a reference standard is available less tasting required than triangle test can be used with trained or untrained assessors

Disadvantages

No indication of character or degree of any difference Statistically less powerful than triangle test

Applications

Quality control — use normal product as control Product matching Product or process improvement Panel selection or training

Sensory Evaluation


TWO-OUT-OF-FIVE TEST

Used to determine whether there is a sensory difference between two samples and to selectand monitor panellists. It is statistically very efficient as the probability of guessing correctlythe different two samples from the five samples presented is low. It can be useful when onlya small number of panellists are available. However, sensory fatigue and memory effectsmay affect the test.

As with the triangle and duo-trio tests, assign 3-digit random codes to the samples and thenmake up the scoresheets, taking care to prepare the samples in an identical fashion. Therewill be 20 possible combinations.

Panellists are instructed to assess each product from left to right and select the two samplesthat are different from the other three. Statistical tables exist to determine the significance ofthe result.

“A” – “NOT A” TEST


Used to determine whether test samples in a series are the same as or different from thereference sample. It is an especially useful test where triangle and duo-trio tests cannot beused. This may be the case where comparisons are required between products that have astrong or lingering flavour/aftertaste when you will need to control the time between samplepresentation or if there are differences in appearance. It is also useful to determine assessorsensitivity to a stimulus.

Initially, panellists require familiarisation with the reference or “A” sample. Panellists arethen presented with a series of samples, some of which are the reference sample “A” andsome “not-A”. Generally, the panellist does not have access to the reference “A” whileevaluating the test samples. The panellist must determine whether the sample is the same(“A”) or different (“not-A”) so it is a forced-choice test. Only one type of “not-A” sampleexists per test series. Panellists may test one, two or up to 10 samples in series (depending onfatigue factors). The samples are presented randomly with 3-digit codes and one at a time (anassessment is made and recorded before proceeding to the next sample). All samples areprepared in an identical way and are representative of the product. The analysis of the data isquite complex.DIFFERENCE-FROM-CONTROL TEST (DFC)

Also called the degree of difference (DOD) test.There is no Australian Standard this test however further information can be obtained inMeilgaard, Civille and Carr and Aust et al. 1985.


This test is used to determine whether or not a perceptible overall difference exists betweenone or more samples and a control sample and also to give an indication as to the size of anydifference perceived. In quality control situations, trained panellists may also be able to ratethe degree of difference for individual attributes.

Sensory Evaluation


A difference from control test is a useful test to use when other difference tests, such astriangle or duo-trio are not suitable because of the normal heterogeneity of the products to betested. For example with products such as meats, baked goods and horticultural products itcan be difficult to obtain a homogeneous sample which is necessary for a triangle or duo triotest.

When used in conjunction with consumer acceptability testing and descriptive testing using atrained panel, the DFC test is useful for quality control and shelf life testing. In these casesthe relative size of the difference is important for deciding whether the product is an accept orreject. It can be used to check production samples for the degree of difference from arecognised control or standard product. In this situation the panellists must be familiar withthe range of differences expected and will require some training with reference samples andthe use of the scale. The test can also be useful in product development situations todetermine which sample is closest to a target product.

Principle

Each panellist is presented with an identified control sample plus one or more test samples.The panellists are asked to rate the size of difference between each test sample and theidentified control sample. Panellists are informed that some of the test samples may be thesame as the control sample. The mean difference from control for each test sample iscompared with the mean difference from control obtained from the blind presentation of thecontrol sample.

The blind control sample is included as a measure of the placebo effect as it is very rare thatthe blind control will actually be rated as absolutely identical to the identified control.

Panellists

Generally 20-50 people are required. Panellists may be trained or untrained but not a mixtureof the two. For some applications such as in a quality control, the panellists would requiresome training. All panellists should be familiar with the test format, how to use the scale andalso be aware that some of the samples will be blind controls.


All samples should be representative of the product and all prepared in exactly the same way.Label an identified control sample for each panellist. Label additional blind control samplesas well as the test sample(s) with 3 digit blinding codes. Where possible the control sampleand samples for assessment should be presented simultaneously. Each panellist evaluates theidentified control sample first. The panellists then rate the degree of difference for each testsample of which some samples will be the blind control. The order of presentation of the testand blind control samples should be balanced.

For example, half the panellists assess the samples in the order:

1. Identified control vs blind control 2. Identified control vs test sample

While the other half assess the samples as:

Sensory Evaluation


1. Identified control vs test sample 2. Identified control vs blind control

Examples of scales that may be used for the difference from control test:

Verbal Category

No differenceVery slight differenceSlight/moderate differenceModerate differenceModerate/large differenceLarge differenceVery large difference

Numerical category Scale

0 = No difference123456789 = Very large difference

Sensory Evaluation


Line scale

no difference very large difference

Analysis of Results

Calculate the mean difference from the identified control for each of the test samples and theblind control samples. If several samples have been evaluated, use a randomised blockanalysis of variance using the panellists as blocks. If only one test sample has been evaluateduse a paired t-test to analyse the results.

ExampleA company suspects a flavouring ingredient may have been left out of a batch of chunkyvegetable soup. They want to know if this batch of soup is perceived to be different or notfrom a control batch of soup. Due to the natural degree of batch to batch variability with theproduct, a triangle test or other forced choice difference would be unsuitable due to the riskof yielding false positives or false negatives.

DIFFERENCE FROM CONTROL TEST Name: Date: Time: Product:........................................................................................ . Assess the sample marked “control” first. Assess sample 386 and score the overall sensory difference between the two samples using thescale below.

not different very different REMEMBER THAT A DUPLICATE CONTROL IS THE SAMPLE SOME OF THE TIME.

Sensory Evaluation


DIRECTIONAL DIFFERENCE TESTS

PAIRED COMPARISON TEST



Used to determine how a specific sensory property differs between two samples. It can beapplied to determine a directional difference (e.g. which sample is sweeter).

A paired comparison test has numerous applications in product or process development, egsubstitution of a new low-calorie sweetener, in quality assurance as well as in storage testsand in product matching. A paired comparison test can also be used to determine if a moreadvanced sensory test should be applied.

The paired comparison test can be used for multiple comparisons, but this results in a largenumber of pairs to assess which uses a lot of sample and can cause sensory fatigue. In thissituation it is better to use a rating test.

Before the sensory testing commences, it is necessary to decide whether the results will betreated as a unilateral or bilateral test. The most common paired comparison tests are two-sided (bilateral) where there is no prior expectation of the result. Conclusions that can bedrawn are that there is no evidence of a difference or that one sample has a greater intensityof the chosen attribute or is preferred.

One sided tests (unilateral) also exist when there is prior expectation of the direction ofdifference. Conclusions to be drawn include that there is no evidence of a difference or thatthe previously declared sample is greater in the attribute intensity or is preferred. Thewording used on bilateral and unilateral score sheets is different.

Test principle

Two coded samples are presented. The panellists complete the scoresheet questions that havebeen previously determined by the test objective.

Panellists

The test is fairly simple requiring minimal training but the panellists must understand theattribute that is being tested. However, trained panellists may be selected if appropriate.Twenty is a reasonable number when the panellists have been screened. Statistically,numbers can be reduced to 7 for a trained panel, but when using completely untrained tasterssuch as consumers, then much larger numbers (100+) are needed.


Two 3-digit randomly coded samples, one of each product, are presented. The samplepresented is representative of the product and all samples are prepared identically. Equalnumbers of AB and BA are randomly allocated to the panellists. Panellists are instructed to

Sensory Evaluation


assess the samples in a specific order (left to right) and identify which has the higher level ofa particular attribute or is preferred. The test is a forced choice test and ‘no difference’responses are not allowed.

Analysis of results

Use standard statistical tables for unilateral tests (Table 3) and bilateral tests (Table 4). Countthe number of replies identifying a particular sample most frequently. Compare this valuewith the number shown in the statistical table for the number of panellists used.

Questionaires

UNILATERAL PAIRED COMPARISON TEST

Name……………………….Date………………………….Time…………

In front of you are two coded samples of orange juice.

Please assess them in the order shown below from left to right and indicate if sample 016is sweeter than sample 983. Circle the response below.

Please cleanse your palate between samples.

YES NO


Comments……………………………………………………………………

BILATERAL PAIRED COMPARISON TEST

Name……………………….Date………………………….Time…………

In front of you are two coded samples of orange juice.

Please assess them in the order shown below from left to right and indicate which sampleis sweetest by circling the appropriate code.

Please cleanse your palate between samples.

Sample code 016 Sample code 983


Comments……………………………………………………………………….

Sensory Evaluation


Examples

Bilateral test

Two drinks ‘A’ and ‘B’, are offered to a panel of 30 assessors. The two samples arepresented under a random number, eg: ‘789’ and ‘379’. The test supervisor accepts a 5%level of significance (ie: P< 0.05%). He does not know which of the two samples containsmore sugar.

Question: Which sample is sweeter?Replies 18 opt for sample ‘A’

12 opt for sample ‘B’From Table 4 it can be concluded that there is no significant difference in the sweetness ofthe two drinks.

Unilateral test

Two drinks, ‘A’ and ‘B’, are offered to a panel of 30 assessors. The two samples arepresented under a random number eg: ‘789’ and ‘379’. The test supervisor accepts a 1% levelof significance (ie: P<0.01%). He knows that drink ‘A’ contains more sugar than drink ‘B’.

Question: Is sample ‘A’ sweeter than sample ‘B’?Replies 22 yes and 8 No.

From Table 3, it can be concluded that drink ‘A’ is significantly sweeter than drink’B’.

Advantages/Disadvantages

See paired preference.

Applications

Product Development Quality Control Shelf Life Measurement

RANKING TEST

(Australian Standard 2542.2.6)


The ranking test can be considered an extension of the paired comparison test. It is used toplace a series of three or more samples in a rank order to determine whether differences existbetween samples. Samples are ranked for a specified criterion, e.g. an attribute (bitterness,crunchiness, hardness) or a preference. The criterion needs to be understood by thepanellists. The data obtained is ordinal and therefore provides directional differences betweensamples but does not provide information about the degree of difference.

The ranking test is a simple way to compare samples and is useful for reducing the number of

Sensory Evaluation


test samples prior to performing another test and to evaluate panellist ability. In productdevelopment, a ranking test can be used as a quick method of indicating the effects ofdifferent raw materials, processing, or packaging and storage treatments.

Test principle

Samples are presented to the panellists simultaneously and are placed by the panellists into arank order relative to one another according to the specified criterion.

Panellists

Minimum of 8 but a larger number of panellists is better.

Preparation and Presentation

Three or more 3-digit random coded samples are presented to panellists simultaneously forassessment in a balanced or random (if more than 4 samples) order. All the samples areprepared and presented identically. The maximum number of samples will depend on thetype of product. They are instructed to arrange the samples in rank order according to thelevel of the specified criterion, and are instructed whether to assign rank 1 for the lowest orhighest level. It is a forced choice test and tied rankings are not permitted. A separatescoresheet is used and completed separately if the rank order is required for more than onecriterion.

As a panellist, it is often easier to perform this test by arranging the samples in a provisionalorder first and then to re-evaluate them before assigning final ranks.

Analysis of results

Rank totals are calculated for each sample and used to generate test statistics which arecompared to statistical tables. As samples are evaluated only in relation to each other, resultsfrom one test cannot be compared to those from another unless they both tested the samesamples.

ExampleA cordial manufacturer has been provided with two new samples of lemon flavour that arecheaper than the existing flavour. The manufacturer wants to know if cordials are made atthe same flavour intensity, would it be cheaper to use either of the two new flavours.Samples are prepared at the same concentration but in order to test this from a sensoryperspective the 3 samples are presented to 30 assessors who are asked to rank them in orderof flavour intensity. The results are presented below:

Sensory Evaluation


Cordial SamplesAssessorA B C

1 1 2 32 1 3 23 2 1 34 1 3 25 3 2 16 1 2 37 1 3 28 3 2 19 3 2 110 3 2 111 2 1 312 3 2 113 1 2 314 3 1 215 3 2 116 1 2 317 2 3 118 1 3 219 1 2 320 2 1 321 3 1 222 2 1 323 1 3 224 3 2 125 1 3 226 1 3 227 3 2 128 3 2 129 1 2 330 2 1 3

Rank Sums 58 61 61

)13(303)616158()13(330

12 222 +×−+++×

=F

= 360.2-360 = 0.2

From Table 7 the critical value for F with 2 degrees of freedom (df = number of samples –1)is 5.99.

The technician must retain the null hypothesis that there is no difference between the flavourstrength of the three products.

RATING TEST

Sensory Evaluation


(Australian Standard 2542.2.3 1988)

(AS2542.1.3 1995: 7.6 Selection of assessors for rating methods and 7.7 Selection ofassessors for descriptive analysis)

The rating test can be used to measure the perceived intensity of sensory characteristics egdegree of strawberry flavour in a strawberry milkshake.

For this type of test the basic principles of sensory evaluation should be followed eg codedsamples, controlled test environment, number of samples tested. Panellists should be selectedbased on their ability to give consistent ratings to the same sample and to discriminatebetween samples checked by statistical analysis. The number of panellists used depends onthe degree of training but generally a minimum of eight highly trained, more if less trained.Selection and training of panellists will be discussed later in a separate section.

The response scale used for rating may be in the form of a category scale or a line scale. Acategory scale is a series of 7 – 15 boxes labelled to identify levels of intensity. With a linescale, panellists respond by marking a position on a horizontal line labelled with “anchors” ateach end. An advantage of this type of scale is that panellists responses are not limited to anumber of categories on the scale and therefore it may be possible to identify moredifferences between samples.

Sensory Evaluation


Example of a category scale.

Strawberry flavourSample number 495 128Extremely strong

Very strong

Moderate

Slight

Absent

An example of a line scale.

Strawberry Flavour

None Very strong

Analysis of results

Ratings must be converted to numerical scores for analysis and interpretation. For categoryscales, successive integers are assigned to successive categories and these are used inanalysis, e.g. with a 9-point scale, the integers 1-9 would be used. For graphic scales, thedistance, e.g. in mm, between the response mark and one end of the scale serves as theresponse score.

The arithmetic mean and standard deviation, when obtained for each sample, serve asmeasures of central tendency and variability, respectively. For statistical analysis, theanalysis of variance technique is appropriate (or a t-test in the case of one or two samples).Correlation or regression analysis may be used for subjective/objective correlations.

Advantages

More than one sensory attribute can be examined. Size and direction of differences can be identified.

Disadvantages

Selecting realistic terminology Agreement and understanding between assessors in descriptive terms Scales are not linear ie: 13 = extremely sweet is not twice as sweet as 7 = moderately

sweet

Sensory Evaluation


Applications

Product Development Quality Control Storage Trials Research

Example

The scoring method was used to determine if there was a difference in bitterness in cheddarcheese made using three different milk-coagulating enzymes. Samples of cheese from eachtreatment were coded and presented to 12 judges for evaluation. The order in which the threesamples were tasted was balanced so that each possible order was used twice: ABC, ACB,BAC, BOA, CAB, CBA.

The ratings assigned by the judges were given numerical values, ranging from 0 points for‘not bitter’ to 5 points for ‘extremely bitter’. The results are shown in the following table.

SamplesJudgesA B C Total

1 3 0 1 42 2 2 2 63 3 1 2 64 1 1 0 25 3 1 3 76 2 1 1 47 3 2 2 78 2 0 1 39 3 1 2 610 4 2 3 911 1 1 0 212 2 2 2 6

Total 29 14 19 62Mean 2.42a 1.17b 1.58b

The results were submitted to analysis of variance.

Any two values not followed by the same letter are significantly different (P<0.05). SampleA is significantly (P,0.05) more bitter than sample C and B. There is no significantdifference (P>.05) in bitterness between samples C and B.

Sensory Evaluation


STATISTICS FOR SENSORY: DIFFERENCE TESTING

What kind of data do we have?

When data are graded, as in rating scales then the t-test or other “parametric” statistics suchas analysis of variance are applied. These are discussed in a different section. In othersituations when we categorise performance into right or wrong answers and count numbers ofpeople who get tests correct or incorrect or those who make one choice over the other we callthis discrete categorical data. For these data we use a special distribution called the binomialdistribution and is useful for tests based on proportions. Some examples of how these testsare used in sensory tests is given below.

Triangle Test

The triangle test is used when we want to know if there is a detectable difference betweentwo samples or products. Three samples are presented where two are the same and one isdifferent. Panellists are asked to pick the odd one out. Purely by luck the panellist has a onein three chance of getting it right.

This forms the basis of the normal approximation to the binomial test. Lets accept that

zp p

pq Nobs=− exp

/ where

pobs is the proportion who answered correctly ie X/Npexp is the proportion of people who we expect by chance ie 1/3q = 1 - pexpz is obtained from tables and for a one tailed risk of 5% is equal to 1.65.

By substituting into the equation and solving for X we get

1 65

13

13

23

. =−

XN

N and

X N N= +0 778 3. /

Now for a range of N values (ie number who sit the test) we can get a range of X values (iethe minimum number who must get the test right). These values have conveniently beencalculated and are already tabulated for use (see tables 1, 2).

For example if we have N = 30 panellists we must have at least

0.778√30 + 30/3or 14.26 correct to achieve significance.

Since we cannot have 0.26 of a person so we round up to 15. Therefore 15 out of 30 peoplemust get the triangle test right in order to reject the null hypothesis and conclude there is adifference among the samples.

Sensory Evaluation


Duo Trio

This is similar to the triangle test except that a standard is presented and two other samples,one of which is the same as the standard, are also given. The panellist has to pick which ofthe two is the same as the standard so has a one in two chance of being correct. Tables forthis are also available but as it is less efficient than the triangle test it is not usually preferredover the triangle test (see table 3).

Paired Comparison Test

Only two samples are given and panellists are asked to pick which sample is, for example,sweeter than the other. The same tables as for the duo trio test can be used and a one-tailedtest is used when you expect one sample to be sweeter (for example) than the other. Whenthere is no preconceived idea of which sample may be sweeter then two-tailed test isappropriate (see tables 3, 4).

Freidman Test

This is best demonstrated by example. Suppose 18 panellists are asked to rank three orangejuices in order of preference. What we want to know is. Are the ranked values for allpanellists the same? The results are as follows.

Panellist RANKA B C

1 1 3 22 2 3 13 1 3 24 1 2 35 3 1 26 2 3 17 3 2 18 1 3 29 3 1 210 3 1 211 2 3 112 2 3 113 3 2 114 2 3 115 2 3 116 3 2 117 3 2 118 2 3 1Sum (column total)Tp

39 43 26

Sensory Evaluation


The Freidman value F needs to be calculated as follows.

FJP P

T J Pp=+

− +∑121

3 12

( )( )

where J - number of judgesP - is the number of samples (products)T1,T2,T3 - are the rank totals for each sample

For our example we get a F of 8.8. Now when the number of panellists is large or the numberof samples exceeds 5 then F follows the chi-squared distribution with P-1 degrees offreedom. So looking up the chi-squared table (table 7) gives a critical value of 5.99. Sinceour calculated F is greater than this we can reject our question and conclude that there aresignificant differences between the samples. Pairwise comparisons can be made using theformula below.

1960 16

. ( )JP P + at the 5% level.

Two samples are different if the difference between their rank sums is greater than or equal to11.76.

Difference from Control Test

Although the difference from control test is a form of difference testing, the data we collect isnot discreet data so the analysis follows the ‘parametric’ tests that we use on rating scales.These are discussed in the Statistics for Sensory: Descriptive Testing section.

Sensory Evaluation


DESCRIPTIVE TESTING

Descriptive testing is used to identify and provide a picture or “profile” of the importantsensory characteristics of a product. With sensory profiling more than two samples can beassessed simultaneously. This type of test has the advantage of not only being able to tell youwhether or not there is a difference between samples but also the nature and magnitude ofthese differences. Appearance, odour, flavour and texture can all be assessed in this way andthe characteristics can be quantified using various techniques and scales as outlined in thissection.

Applications:

• Tracking changes in the sensory characteristics of a product over time for shelf-lifeevaluation

• Examining the sensory properties of a target product for new product development• Examining sensory characteristics of different varieties of a product eg to look at

several varieties of apples in order to identify which varieties are sweetest, crunchiestetc.

• Sensory diagnostics of ingredient, process or packaging changes• Correlations with instrumental methods

The Flavour Profile Method® (Arthur D. Little)

This method was developed by Arthur. D. Little in the late 1940’s early 1950’s. It uses apanel of 4-6 trained panellists. Panellists are selected by screening for sensory acuity,interests, attitude and availability. A vocabulary is developed by exposure to a wide range ofproducts from the product category to be assessed. The list is then reviewed and refined andreference standards and definitions applied to each term.

The panellists examine the products and the results are reported to the panel leader. Throughdiscussion in an open session lead by the panel leader, a consensus decision is reached foreach sample. Aroma, flavour and amplitude, which is the balance or blending of the flavour,is assessed in this way. The scales used with this technique involve the use of numbers andsymbols and therefore cannot be analysed statistically. This method is therefore a qualitativedescriptive test. The main disadvantage with this type of test is that a dominant panelmember or the panel leader could easily influence the panels decision.

Sensory Evaluation


Questionnaire for flavour profile of beer

Product Name Date

AROMACharacteristic IntensityHoppyFruitySourYeastyMaltyAmplitude(overall aroma)

FLAVOURCharacteristic IntensityTinglySweetFruityBitterMaltyYeastyMetallicAstringentAmplitude(overall flavour)

Comments

Sensory Evaluation


Profile Attribute Analysis®

The Flavour Profile method was renamed the Profile Attribute Analysis with the introductionof numerical scales. Mean scores could then be calculated and the data statistically analysed.However consensus methods are still employed by some people. Again, this runs the risk ofa result being skewed by a dominant personality in the group.

The Texture Profile Method®

This method was developed at General Foods in the 1960’s. It was based on the principles ofthe Flavour Profile method to assess the textural characteristics of a product. Texturalcharacteristics are categorised into three groups, mechanical, geometrical and ‘other’characteristics.

1. Mechanical: relating to the reaction of food to stress eg. hardness, chewiness andadhesiveness

2. Geometrical characteristics: relating to the size, shape and orientation of the particleswithin the food eg. grainy, fibrous and aerated

3. Other characteristics: relating to the perception of the moisture and fat contents of thefood

The order in which the characteristics are assessed is also very important. The order ofassessment is first bite, “chewing” or masticatory second phase and residual or third phase.Panellists are selected on their ability to discriminate between textural differences in theproduct area to be trained. Six to ten panellists are suggested.

Standardised terminology and rating scales are used for the assessments and each scale pointis anchored with a specific food. Initially the technique used an expanded version of theFlavour Profile scale, however more recently category and line scales have been used.

Panellists each make their own individual judgement and then depending on the type of scaleused, a consensus decision is reached or statistical analysis is performed on the data.

Quantitative Descriptive Analysis (QDA®)

This method of descriptive analysis was developed in the 1970’s. Ten to twelve panellists areselected by screening for ability to discriminate between products, their ability to verbalisetheir perceptions and to work as a group. The first step is to expose the panellists to a widerange of products from the product category to be assessed. Each panellist individually listsas many descriptive words possible that describe differences between the products. Hedonicterms such as nice, good, bad, etc are not allowed. Through a group discussion, the list ofdescriptive words is narrowed down to remove duplications and redundant terms until astandardised vocabulary is reached. This standardised vocabulary then needs to be definedwith verbal definitions or reference standards and anchor points for the scale agreed upon.The panel also decides the order in which the terms are to be assessed. During this processthe panel leader only acts to facilitate the discussion and provide references but does notinfluence or lead the panel. Trial evaluations are then carried out using the agreed vocabularyand refinements may be made until the panel is happy with the terms used. The panel leaderevaluates the results from these trial sessions and once confident the results are reliable and

Sensory Evaluation


repeatable the actual assessment can take place. The assessment and trial sessions arecompleted in sensory booths following the basic principles of sensory evaluation. Anunstructured 6-inch or 15cm line scale is used to measure the intensities of the agreedcharacteristics. Several replicates (3+) are required to validate the data. Data is thenanalysed using an analysis of variance. The results are often displayed visually on a spiderweb or star diagram.

Results of ANOVA of orange jelly using QDA

Attribute Brand A Brand B SEM Probability

Orange colour 10.2 7.9 0.62 0.011Orange aroma 7.6 6.9 0.50 0.325Firmness 9.6 6.6 0.64 0.001Tartness 8.6 6.9 0.66 0.072Orange flavour 7.6 6.9 0.72 0.494Foreign flavour 4.3 4.8 0.48 0.464Sweetness 7.1 9.6 0.42 <0.001Rate ofbreakdown

5.1 6.1 0.60 0.242

Sensory Evaluation


Other MethodsOther methods which you may come across in literature but which will not be discussed indetail in this workshop are:

Spectrum Method

This is a descriptive analysis technique developed by Civille to cover any or all ofappearance, aroma, flavour, texture or sound characteristics. Panellists use a standardisedlexicon of terms to evaluate the products. This method requires extensive training of thepanel to use standardised scales anchored with multiple reference points and panellists aretrained to use the scale identically. Data is analysed in a similar way to QDA.

Example of intensity scale values (0 to 15) for firmness.

Scale Reference Sample sizevalue3.0 Aerosol whipped cream Redi whip 1oz5.0 Miracle whip Kraft 1oz8.0 Cheese whiz Kraft 1oz11.0 Peanut butter CPC Best Foods 1oz14.0 Cream cheese Kraft/Philadelphia 1oz

Time Intensity

This is used to track the changes in perception of a particular attribute of a product over time.For example you might rate the intensity of mint flavour perceived in chewing gum over a 3minute period. This can be measured using pencil and paper or using one of the sensorysoftware packages with time intensity facilities.

Free Choice Profiling

Unlike other descriptive testing techniques this method does not use an agreed vocabulary toassess the samples. Each panellist generates their own list of terms and scales, although theymust use these consistently for all samples. The data from this type of assessment is thenanalysed using Generalised Procrustes analysis. The main advantage of this technique is thetime saved on training a panel, however interpretation of individual attributes can besubjective as the terms are not defined as with other descriptive testing methods.

Sensory Evaluation


STATISTICS FOR SENSORY: DESCRIPTIVE TESTING

We mentioned earlier about different types of data and how they are analysed using differentstatistical methods. In this section we will look at the most common form of statisticalanalysis for rating or preference type data, the paired t-test and Analysis of Variance (oneway and two way also known as repeated measures analysis of variance). We will alsointroduce some advanced methods for separating data into logical groups using PrincipalComponent Analysis.

The paired t test

A common question we have in sensory evaluation is when we are comparing two productsor samples and we want to know if they are the same or different. We can use statistics andin particular the paired t test to determine statistical difference. We calculate a t value fromthe formula below and compare it to some tabled values for probabilities less than ouraccepted risk, usually a probability of 0.05.

t = mean of difference scores standard deviation of difference scores/ N

Here is an example taken from O’Mahony. Intensity scores for two products are measured by10 panellists on a 25 point scale.

ScorePanellist Product A Product B Difference - d d2

1 20 22 2 42 18 19 1 13 19 17 -2 44 22 18 -4 165 17 21 4 166 20 23 3 97 19 19 0 08 16 20 4 169 21 22 1 110 19 20 1 1N = 10 d =∑ 10 d 2 68∑ =

d = 1

Now for some calculations.

mean of difference scores, d, = 1

the standard deviation of d is computationally =d d N

N

2 2

1

−

−∑∑ (( ) / )

= 58 9/ = 2.538

so t = =1

2 538 10125

..

The degrees of freedom term

Sensory Evaluation


If we had four flavour scores, and knew three of them plus the variance or standard deviationthen we could calculate the value of the fourth unknown data point. In general, degrees offreedom are equal to the sample size, minus the number of parameters we are estimating. Weneed this value when looking up statistical tables.

The tabulated t value for df = 9, two-tailed, p=0.05 is 2.262 (see table 6). A word on two-tailed and one-tailed test. If we simply wish to test whether a mean is different from thepopulation then we use a two-tailed test. However, if it is directional ie. greater than or lessthan then we need a one-tail test. Our value of 1.25 is less than this so we do not reject ournotion that product A is the same as product B. Our data indicates that the difference scoresare not significantly different from 0.

Analysis of Variance

If we have only two samples we want to compare then we can use the paired t-test asdescribed earlier and establish a difference if it is there. If we have four samples then wecould do six paired t-tests and cover all possible pairings of the four treatments. Thishowever becomes very inefficient and unreliable as the number of samples increase. Analternative to this is to use a technique known as analysis of variance to compare severalsamples at the same time.

Analysis of variance looks at the amount of variance attributed to the samples or treatmentsand also estimates the error variance or natural variation. By then doing a ratio of thesevariances (ie signal to noise) we can then compare this to tabulated values. The distributionis known as the F distribution and we calculate a F ratio or F test.

Most computer packages now do analysis of variance, sometimes described as one-wayanalysis of variance and two-way analysis of variance. A two-way analysis of variance isused when the same judges or panellists rate the same samples (sometimes called repeatedmeasures). Lets look at an example.

Suppose we have 10 panellists rating three samples of mango for mango flavour intensity ona nine point scale. Their results are entered into a computer that then completes a two-wayanalysis of variance and gives the following table.

Sensory Evaluation


Source of variation d.f Mean square F

Samples 2 23.456 11.80 **Panellists 9 3.667 1.84 nsError 18 1.987

The F ratio for samples is 11.80 which is greater than the tabulated value of 6.01 at P=0.01with 2 and 18 degrees of freedom (often ** indicates significance at P=0.01, * for P=0.05).This means that the variability due to samples is greater than that occurring naturally so thereare differences between the mango flavour intensity of the three mango samples.

Now to further test which pairs are significantly different we have a number of options. Themost common test would be the least significant difference (lsd) test which is based on the t-test. The lsd tells us what the minimum difference between two means must be for there to

be a significant difference. The formula is α ,dft emsn2

where ems is the error mean

square and n is the number of observations per sample and t come from tables of calculatedvalues.

In this example the lsd (P=0.01) is 1.32, so any two means with a difference greater than thislsd are significantly different.

Other pairwise comparison tests are Duncan’s multiple range and Tukeys honestly significantdifference (HSD). Formulas for these tests can be found in most statistical textbooks or insome cases the computer package may do the test for you.

You will also note that the panellist’s F ratio is not significant (ns), indicating the averagescore given by any one judge is not that different to another judge’s score. Quite often thepanellists F ratio is significant, indicating that they are using different parts of the scale. Withhighly trained panels, panellists tend to agree on the use of the scales.

An extension to the two-way analysis of variance is the three-way analysis of variance wherewe add replicates to the AOV table to provide a complete analysis of the experimental data.

Difference from Control Test

The analysis of the data from this test can take a number of forms but I will outline the mostcommon and simplest to use. If you have a blind control and one test sample then you canperform a paired t-test. If you have more than two samples then you can use analysis ofvariance techniques and pairwise comparisons to determine differences.

An example taken from Meilgaard et al is given below. Forty-two judges are asked tomeasure the perceived overall sensory difference between two prototypes (samples F and N)and the regular analgesic cream (control). A category scale is used where 0 is no differenceand 10 is extreme difference.

Sensory Evaluation


Difference from control test – Analgesic cream

Judge Blindcontrol

ProductF

ProductN

Judge Blindcontrol

ProductF

ProductN

1 1 4 5 22 3 6 72 4 6 6 23 3 5 63 1 4 6 24 4 6 64 4 8 7 25 0 3 35 2 4 3 26 2 5 16 1 4 5 27 2 5 57 3 3 6 28 2 6 48 0 2 4 29 3 5 69 6 8 9 30 1 4 710 7 7 9 31 4 6 711 0 1 2 32 1 4 512 1 5 6 33 3 5 513 4 5 7 34 1 4 414 1 6 5 35 4 6 515 4 7 6 36 2 3 616 2 2 5 37 3 4 617 2 6 7 38 0 4 418 4 5 7 39 4 8 719 0 3 4 40 0 5 620 5 4 5 41 1 5 521 2 3 3 42 3 4 4Mean 2.4 4.8 5.4

Source of variation d.f Mean square F

Judge 41 6.183 6.04 **Product 2 105.365 102.93 **Error 82 1.024

Sample means with Fishers LSD0.05 = 0.44

Sample Blind control Product FMean response 2.4a 4.8b

Sample Blind control Product NMean response 2.4a 5.4b

Within a row, means not followed by a similar letter are significantly different at the 95%confidence level.

It is concluded that both samples F and N were found to be significantly different from thecontrol. Descriptive testing is recommended to determine the nature of these differences.

Sensory Evaluation


Advanced analysis using principal components

When we have lots of data and have asked our panel a number of questions we need atechnique for reducing the data down to a manageable size. The aim of the technique is toreduce the number of variables that describe a sample to that of fewer dimensions. If wereduce to two then we can plot the results onto a graph. These two dimensions are calledprincipal components and are a linear combination of the original variables.

It is useful for classifying a number of products by grouping them according to the variablesthat describe them. Below is an example of the separation of nine coffees using principalcomponents.

Roast

Fragrant

Cereal

Wetwood

Sweet

Oil

Vittoria Australian Blend Robert Timms Mocha KenyaNSW SL 34 QLD SE 8Douwe Egbert premium Melita Colombian Premium StyleAndronicus Mocha Kenya Robert Timms New Guinea GoldHarris Gold Label

Sensory Evaluation


SELECTION, TRAINING AND MOTIVATION OF A PANEL

When developing a sensory panel, there are several areas that need to be addressed that include:

The need for a panel in the organisation (R&D, QA/QC) Organisation and management support and commitment (time and money) Resources required

o Sensory staffo Interest and availability of potential panellistso Samples and references for screening and trainingo Availability of a panel room and boothso Facilities for data collection and statistical analysis

Establishment of a trained sensory panel can be divided into 2 steps:

Selection Training

Selection for Descriptive Testing (Australian Standard 2542.1.3 - 1995)

Recruitment

Panel members are usually recruited from staff in laboratories, offices and the plant of acompany. Some companies test their products at a different company facility. Externalpanellists may also be recruited from the community nearby if the sensory panel work isgoing to be very time consuming.

Talks, circulars, noticeboards or personal invitations may be used to recruit potentialpanellists. Information should be provided to the prospective panellists concerning theapplication of sensory evaluation, what will be involved for the panellists and the envisagedwork program.

Pre-screening questionnaire

Potential panellists need to complete a pre-screening questionnaire to obtain backgroundinformation on their:

interest in participating in the screening and training program as well as ongoing work availability general good health (note any illnesses or allergies and permanent impairment to the

senses) any food idiosyncrasies (strong food dislikes or reactions to foods) other information that might be relevant (age, sex, nationality, cultural and religious

background, previous sensory experience, smoking habits)

Panellists should not be asked to assess a food that they dislike.

In a company situation, distribute questionnaires for employees to fill in, detailing the above

Sensory Evaluation


criteria. If you make all the questions optional you will find that the majority of peoplerespond truthfully. Pre-screening questionnaires can also be used to select individuals whocan describe sensory concepts. Record all the information you receive in some form ofdatabase. Based on the above criteria, decide which prospective panellists are to proceed inthe screening process.

Interview

Individual interviews are required to determine whether prospective panellists will work well ina group situation as well as for the analytical approach required in descriptive testing. Aninterview is also used to confirm interest and availability.

For a descriptive sensory panel, there is a large investment involved in terms of both time andmoney. It is best to complete a thorough screening process rather than training unsuitablesubjects. During the selection process, it is important to make note of both attendance andpersonalities of panellists. A panellist who is repeatedly late or unavailable can be more troublethan they are worth. Someone who distracts other panellists by talking or making comments,despite repeated requests to remain silent while testing, is a liability, not an asset.

However, it is recognised that the best panellists available may need to be used although theymay not necessarily meet all the requirements.

Sensory screening tests

Screening is completed to obtain information on prospective panellists who need to be ableto:

Detect differences in attributes present and their intensities Describe the attributes using verbal descriptors and scaling methods for the different

intensities Be able to recall and apply attribute references when required

Prior to the first screening test, a preliminary session is a good idea to set the rules that may needto be enforced politely but firmly.

Instructions for panellists

Avoid eating, drinking, smoking or chewing gum for 30 minutes before testing. Do not talk or distract other panellists while testing. Read any instructions on the scoresheet before starting to evaluate samples. Make sure you evaluate the samples in the required order. Don't forget to fill in your name and the date. Do not discuss samples with other panellists until after they have evaluated the samples. Have confidence in your own judgement. Ignore your personal likes and dislikes.

Sensory screening tests also give the prospective panellists an indication of the methods used insensory analysis. The screening tests used should be chosen with the envisaged sensoryprogram in mind. Basic tastes and odours are commonly used for screening tests as well asmaterials that illustrate the attributes that may be included in the sensory program. Samples of

Sensory Evaluation


the actual food products may also be used.

A series of triangle or duo-trio tests may be completed to assess the ability of the potentialpanellists to detect small differences between stimuli at supra-threshold levels. Preferably,potential panellists should respond correctly 100% of the time.

Matching tests may be used to evaluate the ability of a prospective panellist to distinguishbetween different sensory stimuli.

In order to evaluate the ability of the panellists to describe sensory responses, a series ofproducts can be presented and potential panellists asked to describe the sensory impression. Theproducts used should be related to those that will be used in the envisaged sensory testing.For example, a range of odours may be presented:

Chemical name Name most commonly associated with the odourBenzaldehyde Bitter almonds, ...Octene-3-ol Mushroom, ...Phenyl-2 ethyl acetate Floral, ...Diallyl sulfide Garlic, ...Camphor Camphor, ...Menthol Peppermint, ...Eugenol Clove, ...Anethol Aniseed, ...Vanillin Vanilla, ...Geosmin Musty/mouldy, ...Beta-ionone Violets, raspberries, ...Butyric acid Rancid butter, ...Acetic acid Vinegar, ...Isoamyl acetate Fruit, acid drops, ...Dimethylthiophene Grilled onions, ...

Panellists are given these samples to assess one at a time and asked to describe the odour usinghis/her own words. A system of marking can be devised e.g. 4 points for absolutely correct, 3points for correct in general terms, 2 points for a vague association, 1 point for a wrongassociation and 0 points for no response. A satisfactory level for selection of panellists needs tobe specified in relation to the materials used. Similar techniques can be applied for taste andtexture.

The potential panellists may be screened for their ability to rank or rate products for selectedattributes using the same technique as the final panel will use. All potential panellists arepresented with the samples in the same order. Panellists are chosen if a satisfactory level isattained which will depend on the intensities of the samples used. Also check that they haveused most of the scale.

Sensory Evaluation


Training

In this phase, it is important that the panellists develop confidence as well as the skills forproduct assessment. Panellists must be taught the correct procedures for evaluating samplesand ways to reduce or eliminate sensory adaptation. They must also learn to disregard theirpersonal preferences. Between 40 and 120h of training are required for a descriptive sensorypanel which will depend on the product, the number of attributes as well as the validity andreliability required. A trained panel usually consists of 10-20 panellists.

The initial stage of training involves vocabulary development. The entire range of productsis presented to the panellists. They are instructed to individually assess the sensorydifferences between the samples and record any differences as descriptive words. Oncompletion of this task, the panellists each list the attributes used to describe each sample. Atthis time, it is very important that the panel leader does not lead or judge the descriptivewords generated by the panellist although they can ask for clarification. The panelliststhemselves will usually start to move towards a general consensus once the total attribute listhas been generated.

It is then the role of the panel leader to provide reference standards for the attributes that havebeen previously selected by general panel consensus. The references can be used to help thepanellists to identify and remember a sensory attribute found in the sample. The referencesmay be chemicals, ingredients or products. The panellists then assess the samples alongsidethe references until a consensus is reached regarding the sensory attributes, referencestandards and definitions. This process should continue until the panellists are all happy andunderstand the terms used.

Towards the end of training, a scoresheet is created by the panellists. The panellists decideon the order in which the attributes are to be assessed. Generally the panel leader decides onthe type of scale used, although the panel decides on the verbal anchors to be used.

Once the panellists have become familiar with the samples, references and definitions, panelevaluation sessions are completed that should be similar to the final testing situation. Thepanellists are presented with coded samples in triplicate and asked to rate them using thescoresheets and attribute scales they have trained with. By statistically analysing the data, thepanel leader will be able to determine if further training is required or if the evaluation phase canbegin.

Like any instrument, the performance of individual panellists as well as the panel as a wholeneeds to be monitored to check they are producing reliable results. Reliability is checked bycompleting test replications and the descriptive data obtained is analysed statistically using ananalysis of variance.

Motivation of panellists is one of the most important factors in maintaining an efficient trainedsensory panel. If panellists are motivated and interested they will perform well. For panellists, asense of completing meaningful work is an important source of motivation. When appropriateon completion of a project, feedback should be given to the panel as to the project objectives andoutcomes and the contribution of the sensory results. Individual panellist feedback is alsoimportant. They should be made to feel that attendance at sensory evaluation sessions is

Sensory Evaluation


important. This can be reinforced by running sessions strictly and efficiently to keep their timeinput to a minimum.

Throughout training as well as during ongoing sensory evaluation sessions, it is important tokeep the channels of communications open through panel discussion at the completion of atraining session or a sensory testing session.

Ongoing records of panellists' training and experience are invaluable. In some instances trainingcan occupy more time than the actual experimental testing sessions, especially when you firststart. However, if the job is done correctly right from the start, your trained panel will be one ofthe most valuable resources in the company. Make sure you look after them.

An aside: Expert panels

Panellists who have a great deal of experience in assessing a particular product are often referredto as "Expert tasters". Commodities that utilise expert tasters include the tea, coffee, wine anddairy industries. These panels usually include only 2 or 3 highly trained tasters. These tastersare particularly sensitive to the nuances of a specific product. They also have the ability to carrythe characteristics of standard samples in their sensory memory. It takes a great deal of practiceto develop the skill and requires continued tasting to stay "tuned". They are usually responsiblefor arranging the tasting conditions and samples themselves, in addition to actually tasting andmaking a final report. This type of panel is most frequently used to assign a quality grade to afinished product, as in butter and cheese grading. In the wine and coffee industries one expertmay use these skills to blend individual components to produce a final product with the desiredcharacteristics.

Sensory Evaluation


REPORTING

As with any other scientific experiment your sensory testing needs to be reported in a clearand concise manner. The Australian standards for each test type details what should beincluded in the report.

The results obtained should be interpreted and conclusions drawn using all the informationgathered in the experiment. Recommendations may also need to be included depending onthe nature of the work.

Remember that it is much easier to write the report if you keep a record as you go along!

Sensory Evaluation


SELECTED BIBLIOGRAPHY

American Meat Science Association, “Guidelines for Cookery and Sensory Evaluation ofMeat”, AMS, USA, 1978.

Amerine, M A, Pangborn, R M and Roessler, E B, “Principles of Sensory Evaluation ofFood”, New York: Academic Press, 1965.

ASTM, “Manual on Sensory Testing Methods”, STP 434, Am. Soc. Test. Makr.,Philadelphia, Pennsylvania, 1968.

Aust, L B, Gacula, M C, Beard,S A and Washam, R W. “Degree of Difference Test Methodin Sensory Evaluation of Heterogeneous Product Types. Journal of Food Science, 50: 511 –513, 1985

Bartoshuk, L, “Separate worlds of taste” Psychology Today 14 (9): 48-57, 1980.

Bartoshuk, L M, “The biological basis of food perception and acceptance” Food Quality &Preference 4: 21-32, 1993.

Bourne, M C, “Food Texture and Viscosity: Concept and Measurement”, Academic PressInc., California, 1982.

Chi-Tang Ho, Manley, C H, “Flavor Measurement”, Marcel Dekker, Inc. 1993.

Gacula M C., “Design and analysis of Sensory Optimization”, Food & Nutrition Press. 1993.

Gacula, M C and Singh, J, “Statistical Methods in Food and Consumer Research, New York:Academic Press, 1984.

Jellinek, G, “Sensory Evaluation of Food: Theory and Practice”, Chichester: EllisHorwood; 1985.

Lawless, H T, “Pepper potency and the forgotten flavour sense” Food Technology 43 (11):52, 57-58, 1989.

Lawless, H T & Heymann, H, “Sensory Evaluation of Food: Principles and Practices”,Chapman & Hall, New York, 1998.

Lyman, B, “A Psychology of Food”, Van Nostrand Reinhold Co. Inc., New York, USA,1989.

Lyon, D H, Francombe, M A, Hasdell, T A and Lawson, K, (editors) “Guidelines forSensory Analysis in Food Product Development and Quality Control”. Chapmann and Hall,London, UK, 1992.

McBride, R L, “The Bliss Point Factor”, Sun Books, Australia, 1990.

Sensory Evaluation


McBride, R L, (editor), “Psychological Basis of Sensory Evaluation”, Elsevier AppliedScience, London, UK, 1990.

McRae, R, Robinson, R K & Sadler, M J (eds) “Encyclopedia of Food Science, FoodTechnology and Nutrition”, Volume 6, Academic Press, London, 1993.

Meilgaard, M, Civille, G V and Carr, B T, “Sensory Evaluation Techniques: Boca Raton,Fla: CRC Press, 1999. (3rd Edition)

Miflora Minoza-Gatchalian, “Sensory Evaluation Methods with Statistical Analysis (forResearch Product Development and Quality Control)”. 1981.

Moskowitz, H R, “New Directions for Product Testing and Sensory Analysis of Foods”, Food& Nutrition Press, Inc. 1985.

Moskowitz, H, “Applied Sensory Analysis of Food”, Volumes 1 and 2, CRC Press, Florida,USA, 1988.

O’Mahoney, M, “Sensory Evaluation of Food: Statistical Methods and Procedures”, NewYork: Marcel Dekker, Inc, 1986.

O’Mahony, M & Ishii, I “Do you have an umami tooth?” Nutrtion Today May/June, 1985.

Piggott, J R, “Sensory Analysis of Food”, London: Elsevier Applied Science, 1988 (2ndedition now available).

Piggott, J R, “Statistical Procedures in Food Research”, London: Elsevier Applied Science,1986.

Piggott, J R, Paterson, A “Understanding Natural Flavors”. Blackie Academic &Professional. 1994.

Poste, L M, Mackie, D A, Butter, G and Larmond, E, “Laboratory Methods for SensoryAnalysis of Food”, Agriculture Canada Publication 1864/E, 1991.

Rutledge, K P and Hudson, J M, “Sensory Evaluation: Method for Establishing and Traininga Descriptive Flavour Panel, Food Technology 44 (12): 78-84, 1990.

Stone, H and Sidel, J L, “Sensory Evaluation Practices”, 2nd edition, New York: AcademicPress, 1992.

Thomson, D M H, “Food Acceptability”, Elsevier Applied Science, London, UK, 1988.

Sensory Evaluation


JOURNALS

Gacula, M C, “Journal of Sensory Studies”. Food & Nutrition Press, Inc.

MacFie, H J., Meiselman, H L., “Food Quality and Preference”. Elsevier Applied Scien


STATISTICAL TABLES

Table 1: Probability of X or More Correct Judgments in n Trials (one-tailed, p = 1/3)a

n\x 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 285 868 539 210 045 0046 912 649 320 100 018 0017 941 737 429 173 045 0078 961 805 532 259 088 020 0039 974 857 623 350 145 042 008 00110 983 896 701 441 213 077 020 00311 988 925 766 527 289 122 039 009 00112 992 946 819 607 368 178 066 019 004 00113 995 961 861 678 448 241 104 035 009 00214 997 973 895 739 524 310 149 058 017 004 00115 998 981 921 791 596 382 203 088 031 008 00216 998 986 941 834 661 453 263 126 050 016 004 00117 999 990 956 890 719 522 326 172 075 027 008 00218 999 993 967 898 769 588 391 223 108 043 014 004 00119 995 976 921 812 648 457 279 146 065 024 007 00220 997 982 940 848 703 521 339 191 092 038 013 004 00121 998 987 954 879 751 581 399 240 125 056 021 007 00222 998 991 965 904 794 638 460 293 163 079 033 012 003 00123 999 993 974 924 831 690 519 349 206 107 048 019 006 00224 999 995 980 941 862 737 576 406 254 140 068 028 010 003 00125 999 996 985 954 888 778 630 462 304 178 092 042 016 006 00226 997 989 964 910 815 679 518 357 220 121 058 025 009 003 00127 998 992 972 928 847 725 572 411 266 154 079 036 014 055 00228 999 994 979 943 874 765 623 464 314 191 104 050 022 008 003 00129 999 996 984 955 897 801 670 517 364 232 133 068 031 013 005 00130 999 997 988 965 916 833 714 568 415 276 166 090 043 019 007 002 00131 998 991 972 932 861 754 617 466 322 203 115 059 027 011 004 00132 998 993 978 946 885 789 662 516 370 243 144 078 038 016 066 002 00133 999 995 983 957 905 821 705 565 419 285 177 100 051 023 010 004 00134 999 996 987 965 922 849 744 612 468 330 213 126 067 033 014 006 002 00135 999 997 990 973 937 873 779 656 516 376 252 155 087 044 020 009 003 00136 998 992 978 949 895 810 697 562 422 293 187 109 058 028 012 005 002 00147 998 994 963 959 913 838 735 607 469 336 223 135 075 038 018 007 003 00138 999 996 987 967 928 863 769 650 515 381 261 164 095 051 025 011 004 002 00139 999 997 990 973 941 885 800 689 560 425 301 196 118 066 033 016 007 003 00140 999 997 992 979 952 903 829 726 603 470 32 231 144 083 044 021 010 004 00141 998 994 983 961 920 854 761 644 515 385 268 173 104 057 029 014 006 002 00142 999 995 987 968 933 876 791 683 558 428 307 205 127 073 038 019 008 003 00143 999 996 990 974 945 895 820 719 600 471 347 239 153 091 050 025 012 005 002 00144 999 997 992 980 955 912 845 753 639 514 389 275 182 111 063 033 016 007 003 00145 999 998 994 984 963 926 867 783 677 556 430 313 213 135 079 043 022 010 004 002 00146 998 995 987 970 938 887 811 713 596 472 352 246 161 098 055 029 014 006 003 00147 999 996 990 976 949 904 836 745 635 514 392 282 189 119 070 038 019 009 004 002 00148 999 997 992 980 958 919 859 776 672 554 433 318 220 142 086 048 025 012 006 002 00149 999 998 994 984 965 932 879 803 706 593 473 356 253 168 105 061 033 017 008 003 00150 999 998 995 987 972 943 896 829 739 631 513 395 287 196 126 076 042 022 011 005 002 001


Table 2: Minimum Numbers of Correct Judgments to Establish Significance at Various ProbabilityLevels for the Triangle tests (one tailed, p = 1/3)

Probability Levels

No. of trials (n) 0.05 0.04 0.03 0.02 0.01 0.005 0.0015 4 5 5 5 5 56 5 5 5 5 6 67 5 6 6 6 6 7 78 6 6 6 6 7 7 89 6 7 7 7 7 8 810 7 7 7 7 8 8 911 7 7 8 8 8 9 1012 8 8 8 8 9 9 1013 8 8 9 9 9 10 1114 9 9 9 9 10 10 1115 9 9 10 10 10 11 1216 9 10 10 10 11 11 1217 10 10 10 11 11 12 1318 10 11 11 11 12 12 1319 11 11 11 12 12 13 1420 11 11 12 12 13 13 1421 12 12 12 13 13 14 1522 12 12 13 13 14 14 1523 12 13 13 13 14 15 1624 13 13 13 14 15 15 1625 13 14 14 14 15 16 1726 14 14 14 15 15 16 1727 14 14 15 15 16 17 1828 15 15 15 16 16 17 1829 15 15 16 16 17 17 1930 15 16 16 16 17 18 1931 16 16 16 17 18 18 2032 16 16 17 17 18 19 2033 17 17 17 18 18 19 2134 17 17 18 18 19 20 2135 17 18 18 19 19 20 2236 18 18 18 19 20 20 2237 18 18 19 19 20 21 2238 19 19 19 20 21 21 2339 19 19 20 20 21 22 2340 19 20 20 21 21 22 2441 20 20 20 21 22 23 2442 20 20 21 21 22 23 2543 20 21 21 22 23 24 2544 21 21 22 22 23 24 2645 21 22 22 23 24 24 2646 22 22 22 23 24 25 2747 22 22 23 23 24 25 2748 22 23 23 24 25 26 2749 23 23 24 24 25 26 2850 23 24 24 25 26 26 2860 27 27 28 29 30 31 3370 31 31 32 33 34 35 3780 35 35 36 36 38 39 4190 38 39 40 40 42 43 45


Table 3: Minimum Numbers of Correct Judgments to Establish Significance at Various ProbabilityLevels for Paired - Comparison and Duo-Trio Tests (one-tailed, p=1/2)

Probability levels

No of trials (N) 0.05 0.04 0.03 0.02 0.01 0.005 0.0017 7 7 7 7 78 7 7 8 8 8 89 8 8 8 8 9 910 9 9 9 9 10 10 1011 9 9 10 10 10 11 1112 10 10 10 10 11 11 1213 10 11 11 11 12 12 1314 11 11 11 12 12 13 1315 12 12 12 12 13 13 1416 12 12 13 13 14 14 1517 13 13 13 14 14 15 1618 13 14 14 14 15 15 1619 14 14 15 15 15 16 1720 15 15 15 16 16 17 1821 15 15 16 16 17 17 1822 16 16 16 17 17 15 1923 16 17 17 17 18 19 2024 17 17 18 18 19 19 2025 18 15 18 19 19 20 2126 18 18 19 19 20 20 2227 19 19 19 20 20 21 2228 19 20 20 20 21 22 2329 20 20 21 21 22 22 2430 20 21 21 22 22 23 2431 21 21 22 22 23 24 2532 22 22 22 23 24 24 2633 22 23 23 23 24 25 2634 23 23 23 24 25 25 2735 23 24 24 25 25 26 2736 24 24 25 25 26 27 2837 24 25 25 26 26 27 2938 25 25 26 26 27 28 2939 26 26 26 27 28 28 3040 26 27 27 27 28 29 3041 27 27 27 28 29 30 3142 27 28 28 29 29 30 3243 28 28 29 29 30 31 3244 28 29 29 30 31 31 3345 29 29 30 30 31 32 3446 30 30 30 31 32 33 3447 30 30 31 31 32 33 3548 31 31 31 32 33 34 3649 31 32 32 33 34 34 3650 32 32 33 33 34 35 3760 37 38 38 39 40 41 4370 43 43 44 45 46 47 4980 48 49 49 50 51 52 5590 54 54 55 56 57 58 61100 59 60 60 61 63 64 66

Source : .E.B .Roessler et al.. Journal of Food Science, 1978, 43, 940-947


Table 4: Minimum Numbers of Agreeing Judgements Necessary to Establish Significance at VariousProbability Levels for the Paired – Preference Tests and Difference (two tailed, p=1/2).

Probability LevelsNo. of trials (n) 0.05 0.04 0.03 0.02 0.01 0.005 0.0017 7 7 7 78 8 8 8 8 89 8 8 9 9 9 910 9 9 9 10 10 1011 10 10 10 10 11 11 1112 10 10 11 11 11 12 1213 11 11 11 12 12 12 1314 12 12 12 12 13 13 1415 12 12 13 13 13 14 1416 13 13 13 14 14 14 1517 13 14 14 14 15 15 1618 14 14 15 15 15 16 1719 15 15 15 15 16 16 1720 15 16 16 16 17 17 1821 16 16 16 17 17 18 1922 17 17 17 17 18 18 1923 17 17 18 18 19 19 2024 18 18 18 19 19 20 2125 18 19 19 19 20 20 2126 19 19 19 20 20 21 2227 20 20 20 20 21 22 2328 20 20 21 21 22 22 2329 21 21 21 22 22 23 2430 21 22 22 22 23 24 2531 22 22 22 23 24 24 2532 23 23 23 23 24 25 2633 23 23 24 24 25 25 2734 24 24 24 25 25 26 2735 24 25 25 25 26 27 2836 25 25 25 26 27 27 2937 25 26 26 26 27 28 2938 26 26 27 27 28 29 3039 27 27 27 28 28 29 3140 27 27 28 28 29 30 3141 28 28 28 29 30 30 3242 28 29 29 29 30 31 3243 29 29 30 30 31 32 3344 29 30 30 30 31 32 3445 30 30 31 31 32 33 3446 31 31 31 32 33 33 3547 31 31 32 32 33 34 3648 32 32 32 33 34 35 3649 32 33 33 34 34 35 3750 33 33 34 34 35 36 3760 39 39 39 40 41 42 4470 44 45 45 46 47 48 5080 50 50 51 51 52 53 5690 55 56 56 57 58 59 61100 61 61 62 63 64 65 67


Table 5a 5 % Points for the Distribution of F

n2\n1 1 2 3 4 5 6 8 12 24 81 161.40 199.50 215.70 224.60 230.20 234.00 238.90 243.90 249.00 254.302 18.51 19.00 19.16 19.25 19.30 19.33 19.37 19.41 19.45 19.503 10.13 9.55 9.28 9.12 9.01 8.94 8.84 8.74 8.64 8.534 7.71 6.94 6.59 6.39 6.26 6.16 6.04 5.91 5.77 5.635 6.61 5.79 5.41 5.19 5.05 4.95 4.82 4.68 4.53 4.366 5.99 5.14 4.76 4.53 4.39 4.28 4.15 4.00 3.84 3.677 5.59 4.74 4.35 4.12 3.97 3.87 3.73 3.57 3.41 3.238 5.32 4.46 4.07 3.84 3.69 3.58 3.44 3.28 3.12 2.939 5.12 4.26 3.86 3.63 3.48 3.37 3.23 3.07 2.90 2.7110 4.96 4.10 3.71 3.48 3.33 3.22 3.07 2.91 2.74 2.5411 4.84 3.98 3.59 3.36 3.20 3.09 2.95 2.79 2.61 2.4012 4.75 3.88 3.49 3.26 3.11 3.00 2.85 2.69 2.50 2.3013 4.67 3.80 3.41 3.18 3.02 2.92 2.77 2.60 2.42 2.2114 4.60 3.74 3.34 3.11 2.96 2.85 2.70 2.53 2.35 2.1315 4.54 3.68 3.29 3.06 2.90 2.79 2.64 2.48 2.29 2.0716 4.49 3.63 3.24 3.01 2.85 2.74 2.59 2.42 2.24 2.0117 4.45 3.59 3.20 2.96 2.81 2.70 2.55 2.38 2.19 1.9618 4.41 3.55 3.16 2.93 2.77 2.66 2.51 2.34 2.15 1.9219 4.38 3.52 3.13 2.90 2.74 2.63 2.48 2.31 2.11 1.8820 4.35 3.49 3.10 2.87 2.71 2.60 2.45 2.28 2.08 1.8421 4.32 3.47 3.07 2.84 2.68 2.57 2.42 2.25 2.05 1.8122 4.30 3.44 3.05 2.82 2.66 2.55 2.40 2.23 2.06 1.7823 4.28 3.42 3.03 2.80 2.64 2.53 2.38 2.20 2.00 1.7624 4.26 3.40 3.01 2.78 2.62 2.51 2.36 2.18 1.98 1.7325 4.24 3.38 2.99 2.76 2.60 2.49 2.34 2.16 1.96 1.7126 4.22 3.37 2.98 2.74 2.59 2.47 2.32 2.15 1.95 1.6927 4.21 3.35 2.96 2.73 2.57 2.46 2.30 2.13 1.93 1.6728 4.20 3.34 2.95 2.71 2.56 2.44 2.29 2.12 1.91 1.6529 4.18 3.33 2.93 2.70 2.54 2.43 2.28 2.40 1.90 1.6430 4.17 3.32 2.92 2.69 2.53 2.42 2.27 2.09 1.89 1.6240 4.08 3.23 2.84 2.61 2.45 2.34 2.18 2.00 1.79 1.5160 4.00 3.15 2.76 2.52 2.37 2.25 2.10 1.92 1.70 1.39120 3.92 3.07 2.68 2.45 2.29 2.17 2.02 1.83 1.61 1.258 3.84 2.99 2.60 2.37 2.21 2.09 1.94 1.75 1.52 1.00

Source : Table 9 is taken from Table V of Fisher and Yates : 1974 Statistical Tables for Biological, Agricultural and MedicalResearch published by Longman Group UK Ltd. London (previously published by Oliver and Boyd Ltd. Edinburgh) and bypermission of the authors and publishers.


Table 5b 1 % Points for the Distribution of F

n2\n1 1 2 3 4 5 6 8 12 24 81 4052 4999 5403 5625 5764 5859 5981 6106 6234 63662 98.49 99.00 99.17 99.25 99.30 99.33 99.36 99.42 99.46 99.503 34.12 30.81 29.46 28.71 28.24 27.91 27.49 27.05 26.60 26.124 21.20 18.00 16.69 15.98 15.52 15.21 14.80 14.37 13.93 13.465 16.46 13.27 12.06 11.39 10.97 10.67 10.29 9.89 9.47 9.026 13.74 10.92 9.78 9.15 8.75 8.47 8.10 7.72 7.31 6.887 12.25 9.55 8.45 7.85 7.46 7.19 6.84 6.47 6.07 5.658 11.26 8.65 7.59 7.01 6.63 6.37 6.03 5.67 5.28 4.869 10.56 8.02 6.99 6.42 6.06 5.80 4.47 5.11 4.73 4.3110 10.04 7.56 6.55 5.99 5.64 5.39 5.06 4.71 4.33 3.9111 9.65 7.20 6.22 5.67 5.32 5.07 4.74 4.40 4.02 3.6012 9.33 6.93 5.95 5.41 5.06 4.82 4.50 4.16 3.78 3.3613 9.07 6.70 5.74 5.20 4.86 4.62 4.30 3.96 3.59 3.1614 8.86 6.51 5.56 5.03 4.69 4.46 4.14 3.80 3.43 3.0015 8.68 6.36 5.42 4.89 4.56 4.32 4.00 3.67 3.29 2.8716 8.53 6.23 5.29 4.77 4.44 4.20 3.89 3.55 3.18 2.7517 8.40 6.11 5.18 4.67 4.34 4.10 3.79 3.45 3.08 2.6518 8.28 6.01 5.09 4.58 4.25 4.01 3.71 3.37 3.00 2.5719 8.18 5.93 5.01 4.50 4.17 3.94 3.63 3.30 2.92 2.4920 8.10 5.85 4.94 4.43 4.10 3.87 3.56 3.23 2.86 2.4221 8.02 5.78 4.87 4.37 4.04 3.81 3.51 3.17 2.80 2.3622 7.94 5.72 4.82 4.31 3.99 3.76 3.45 3.12 2.75 2.3123 7.88 5.66 4.76 4.26 3.94 3.71 3.41 3.07 2.70 2.2624 7.82 5.61 4.72 4.22 3.90 3.67 3.36 3.03 2.66 2.2125 7.77 5.57 4.68 4.18 3.86 3.63 3.32 2.99 2.62 2.1726 7.72 5.53 4.64 4.14 3.82 3.59 3.29 2.96 2.58 2.1327 7.68 5.49 4.60 4.11 3.78 3.56 3.26 2.93 2.55 2.1028 7.64 5.45 4.57 4.07 3.75 3.53 3.23 2.90 2.52 2.0629 7.60 5.42 4.54 4.04 3.73 3.50 3.20 2.87 2.49 2.0630 7.56 5.39 4.51 4.02 3.70 3.47 3.17 2.84 2.47 2.0140 7.31 5.18 4.31 3.83 3.51 3.29 2.99 2.66 2.29 1.8060 7.08 4.98 4.13 3.65 3.34 3.12 2.82 2.50 2.12 1.60120 6.85 4.79 3.95 3.48 3.17 2.96 52.66 2.34 1.95 1.388 6.64 4.60 3.78 3.32 3.02 2.80 2.51 2.18 1.79 1.00

Source : Table 9 is taken from Table V of Fisher and Yates : 1974 Statistical Tables for Biological, Agricultural and MedicalResearch published by Longman Group UK Ltd. London (previously published by Oliver and Boyd Ltd. Edinburgh) and bypermission of the authors and publishers.


Table 6: Critical Value of ta

Level of significance for one-tailed test0.1 0.05 0.025 0.01 0.005 0.0005Level of significance for two-tailed test

df 0.2 0.1 0.05 0.02 0.01 0.0011 3.078 6.314 12.706 31.821 63.657 636.6192 1.886 2.92 4.303 6.965 9.925 31.5983 1.638 2.353 3.182 4.541 5.841 12.9414 1.533 2.132 2.776 3.747 4.604 8.615 1.476 2.015 2.571 3.365 4.032 6.8596 1.44 1.943 2.447 3.143 3.707 5.9597 1.415 1.895 2.365 2.998 3.499 5.4058 1.397 1.86 2.306 2.896 3.355 5.0419 1.383 1.833 2.262 2.821 3.25 4.78110 1.372 1.812 2.228 2.764 3.169 4.58711 1.363 1.796 2.201 2.718 3.106 4.43712 1.356 1.782 2.179 2.681 3.055 4.31813 1.35 1.771 2.16 2.63 3.012 4.22114 1.345 1.761 2.145 2.624 2.977 4.1415 1.341 1.753 2.131 2.602 2.947 4.07316 1.337 1.746 2.12 2.583 2.921 4.01517 1.333 1.74 2.11 2.567 2.898 3.96518 1.33 1.734 2.101 2.552 2.878 3.92219 1.328 1.729 2.093 2.539 2.861 3.88320 1.325 1.725 2.086 2.528 2.845 3.8521 1.323 1.721 2.08 2.518 2.831 3.81922 1.321 1.717 2.074 2.508 2.819 3.79223 1.319 1.714 2.069 2.5 2.807 3.76724 1.318 1.711 2.064 2.492 2.797 3.74525 1.316 1.708 2.06 2.485 2.787 3.72526 1.315 1.706 2.056 2.479 2.779 3.70727 1.314 1.703 2.052 2.473 2.771 3.6928 1.313 1.701 2.048 2.467 2.763 3.67429 1.311 1.699 2.045 2.462 2.756 3.65930 1.31 1.697 2.042 2.457 2.75 3.64640 1.303 1.684 2.021 2.423 2.704 3.55160 1.296 1.671 2 2.39 2.66 3.46120 1.289 1.658 1.98 2.358 2.617 3.37300 1.282 1.645 1.96 2.326 2.576 3.2

aThe value listed in the table is the critical value of t for the number of degrees of freedom listed in the leftcolumn for a one- or two-tailed test at the significance level indicated at the top of each column. If theobserved t is greater than or equal to the tables value, reject Ho.

Source: Table III of Fisher and Yates, Statistical Tables for Biological, Agricultural and MedicalResearch, published by Longman Group Ltd, London (previously published by Oliver and Boyd Ltd,Edinburgh) and by permission of the authors and publishers.


Table 7: Critical Values of Chi-Squarea

Level of significance for one-tailed test0.10 0.05 0.025 0.01 0.005 0.0005Level of significance for two-tailed test

df 0.2 0.1 0.05 0.02 0.01 0.0011 1.64 2.71 3.84 5.41 6.64 10.832 3.22 4.6 5.99 7.82 9.21 13.823 4.64 6.25 7.82 9.84 11.34 16.274 5.99 7.78 9.49 11.67 13.28 18.465 7.29 9.24 11.07 13.39 15.09 20.526 8.56 10.64 12.59 15.03 16.81 22.467 9.8 12.02 14.07 16.62 18.48 24.328 11.03 13.36 15.51 18.17 20.09 26.129 12.24 14.68 16.92 19.68 21.67 27.8810 13.44 15.99 18.31 21.16 23.21 29.5911 14.63 17.28 19.68 22.62 24.72 31.2612 15.81 18.55 21.03 24.05 26.22 32.9113 16.98 19.81 22.36 25.47 27.69 34.5314 18.15 21.06 23.68 26.87 29.14 36.1215 19.31 22.31 25 28.26 30.58 37.716 20.46 23.54 26.3 29.63 32 39.2917 21.62 24.77 27.59 31 33.41 40.7518 22.76 25.99 28.87 32.35 34.8 42.3119 23.9 27.2 30.14 33.69 36.19 43.8220 25.04 28.41 31.41 35.02 37.57 45.3221 26.17 29.62 32.67 36.34 38.93 46.822 27.3 30.81 33.92 37.66 40.29 48.2723 28.43 32.01 35.17 38.97 41.64 49.7324 29.55 33.2 36.42 40.27 42.98 51.1825 30.68 34.38 37.65 41.57 44.31 62.6226 31.8 35.56 38.88 42.86 45.64 54.0527 32.91 36.74 40.11 44.14 46.96 55.4828 34.03 37.92 41.34 45.42 48.28 56.8929 35.14 39.09 42.69 46.69 49.59 58.330 36.25 40.26 43.77 47.96 50.89 59.732 38.47 42.59 46.19 50.49 53.49 62.4934 40.68 44.9 48.6 53 56.06 65.2536 42.88 47.21 51 55.49 58.62 67.9938 45.08 49.51 53.38 57.97 61.16 70.740 47.27 51.81 55.76 60.44 63.69 73.444 51.64 56.37 60.48 65.34 68.71 78.7548 55.99 60.91 65.17 70.2 73.68 84.0452 60.33 65.42 69.83 75.02 78.62 89.2756 64.66 69.92 74.47 79.82 83.51 94.4660 68.97 74.4 79.08 84.58 88.38 99.61

aThe table lists the critical values of chi square for the degrees of freedom shown at the left for testscorresponding to those significance levels heading each column. If the observed value of xobs

2 is greaterthan or equal to the tabled value, reject Ho.

Source: Table IV of Fisher and Yates, Statistical Tables for Biological, Agricultural and MedicalResearch, published by Longman Group Ltd, London (previously published by Oliver and Boyd Ltd,Edinburgh) and by permission of the authors and publishers.

sensory evaluation manual

Documents