THEORY & PRINCIPLE OF COLOR

MEASUREMENT

COLOR??COLOR : the sensation – experienced by individual- radiant energy within –light visible spectrum (400-800 nm) –retina of eye.COLORANT : pigment that is used to color a product.COLORIMETRY : the science of color measurement.

COLOR PERCEPTION

Things required to see color

A light source

object

observer

- normally emits light that appears to be white

- when the light is dispersed by a prism it is seen to be made up to all visible wavelength

A light sources

Object-object modify light

- colorants such pigments or dyes , in the object selectively absorb some wavelengths of the incident light while reflecting or transmitting others

- there are three types of cones shaped receptors sensitive to red , green and blue

-luminosity is the relative sensitivity of the human eye to various wavelength of light

-rod shaped receptors in the eye are responsible for night vision

-cone shaped receptors are responsible for day light and color vision

Observer

Factors different perception

• different direction (angle)• different sizes --> color different e.g small more darker• different background --> different brightness• different observer --> various color• Different material --> solid, liquid

e.g liquid sample more dark• Different cross-sectional of cell holder--> > thick , >

darker

COLOR MEASUREMENT

Things required to see colorTo see color: to measure color:

Light sources

Object

Observers

Light sources

Specimen

Spectrometer

Measuring color

A colorimeter spectrophotometer or spectrophotometer

Color scales

Visual organization of color

Visual organizations of color:-color has a degree of lightness or value- hue is the color from the rainbow or spectrum or colors- colorant can be added or increase the amount of chroma or saturation

Measured color values:-visual methods of specifying color are subjective- measuring color using an instrument gives objective results

Quantification of color

-brightness (lightness, L) light or dark- color tone (hue, H)- saturation (chrome, C) vivid : more vivid, saturated subdued

Amount of green-red (-a to +a)

Amount yellow-or-blue (+b to -b)

The brightness (or lightness,L) based on the amount of light reflected or transmitted.

Color opponent theory

State that the red, green and blue cone responses are re-mixed into opponent coders as they move up the optic nerve to the brain

Importance Of Colour Measurement As A Quality

Control Tool

● Uniform● Specific● Attraction● Providing a colorful identity to products

that would otherwise have little colour

CIE Colour Space or Colour Model

Lightness (*L)

Chroma (*c)

Hue (*h)

● Delta E● difference between two colour samples● show how far apart the two samples are in the colour 'sphere' visually

Tips for selecting the right color management instruments

● Select instruments with good repeatability● Ensure instruments have sufficient

measurement area● Software that goes with the colour

measuring instruments

Observations

Part 1

• Colour measurement of – liquid (distilled water) and

– solid sample (Washington apple)

Average Std. Dev

L 30.27333 1.589727

C 22.69667 3.466588

H 21.73333 0.638148

Table 1: Values of L, C and H for distilled water

Table 2: Values of L, C and H for Washington Apple

Average Std. Dev

L 88.64667 0.005774

C 138.0233 0.005774

H 85.74333 0.005774

Figure 1: CIELAB Colour Space

Part 2

• The effect of target mask size on colour parameters– Sample used: US Enza Jazz apple– Target mask sizes

• 3mm• 11mm• 36mm

Aperture's Size (mm) L C H3 40.408 25.497 39.534

11 52.298 43.046 43.97736 56.195 50.16 44.439

0 5 10 15 20 25 30 35 400

10

20

30

40

50

60

Comparison of L,C and H between different target mask sizes

LCH

Table 3: Value of L, C and H of US Enza Jazz apple using different target mask sizes

Part 3

• Effect of optical path length on colour parameters– Sample used

• DNS Solution

– Thickness of cell holder used• 2mm• 10mm• 20mm

Cell thickness (mm) L C H

2 88.677 137.993 86.091

10 81.545 140.154 77.577

20 76.85 136.319 73.469

Table 4: Value of L, C and H of DNS solution using different thickness of cell holders

0 5 10 15 20 250

20

40

60

80

100

120

140

160

Value of L, C and H of DNS solution using different cell holder thickness

LCH

Part 4

• Effect of pH on the colour values of red cabbage– Sample used

• Red Cabbage

– pH used• 3• 5• 7• 9• 11

pH L C H

3 81.62 39.2967 343.613

5 90.53 13.1133 317.543

7 85.6067 24.5267 171.977

9 95.7667 37.01 107.53

11 96.83 38.0333 103.187

Table 4: Value of L, C and H of red cabbage of different pH

2 3 4 5 6 7 8 9 10 11 120

50

100

150

200

250

300

350

400

Value of L, C and H of red cabbage in different pH

LCH

References• http://www.rpdms.com/cielch/index.html• http://allfreshkosher.com/red-delicious-washington-apples-extra-fancy-xl.

html• http://

www.chem.uiuc.edu/webfunchem/grammoleprob/GramMoleProb2.htm• http://www.arboschwin.com/index.php?page=hr1• http://fitlifestyle.blogspot.com/2011/06/healthier-with-red-cabbage.html

STARCH

• Predominant food reserve substances in plant

• Provides 70-80% of the calories consumed by human.

• Made up from polysaccharide and commonly found in food

Source of starch• Cereal grain seeds

– Corn– Wheat– Rice

• Tubers and Roots– Potato– Tapioca– Arrowroot

• Peas• Sago

Starch

Amylose

Amylopectin

Amylose• Straight-chain glucose polymer• Account 15% - 20% of starch • Connected by α-1,4-glycosidic bonds• Molecular weight ranging from 105-106

Amylopectin• Very highly branched molecule• Much larger size that amylose• Branches of the amylopectin molecules are clustered

and occur as double helix• Glucose units are linked by α-1, 4-glycosidic bonds and

α-1, 6-glycosidic bonds

1

6

Starch granule

• Made up of amylose and amylopectin molecule arranged radially

• contain both crystalline and non-crystalline regions in alternating layer.

• The clustered branches of amylopectin occur as packed double helix

• packing together of double-helical structures forms small crystalline lamellae.

• more dense of starch granule, which alternate with less dense amorphous layers, contain greater amounts of the crystalline lamellae.

2µm

Potato starch granule

Corn starch granule

General Properties of Potato Starch and Corn starch

Starch Granule size, μm

Amylose %

Amylopectin %

Pasting temperature, ⁰C

Viscosity Paste clarity

Fat %

Protein %

Phosphorus %

Potato 5-100 21 79 56-65 Very high Clear 0.1 0.10 0.08

Corn 2-30 28 72 62-80 Medium Opaque 0.8 0.35 0.00

Starch granules contain both linear amyloseand branched amylopectin.

Raw, uncooked starch granules heated in water

Swelling is evident

Some granules have collapsed

Amylose AmylopectinDo not contribute significantly to viscosity

Give viscosity to cooked paste

Do not contribute to gel formation

For formation of gel

Advantages:1. Uses small

sample size2. Short testing time3. Ability to modify

testing conditions

Rapid Visco Analyser (RVA) indicates starch viscosity by measuring the resistance of flour and water slurry to the stirring action of a paddle.

RELEVANT OF PASTING PARAMETERS TO PROCESSING STEPS CONSIDERATION

pasting temperature

• Temperature at initial swelling of starch granule,takes place when suspended in water.

• Heating starch granules in suspension in water cause water penetrates the granules to hydrate them and resulting swelling.

• provide indication of minimum temperature required to cook.

peak viscosity

• the highest viscosity reached during gelatinization of starch

• occurs prior to the initiation of sample cooling• indicate water binding capacity of starch

breakdown viscosity

• rate of breakdown in viscosity to a holding strength, hot paste viscosity or trough.

• depend on temperature and degree of mixing or shear rate applied to the mixture and the nature of material.

final viscosity

• the increase in viscosity during cooling of paste.

• a measure of retrogradation due to reassociation of the starch molecules

setback viscosity

• reassociation between starch molecules during cooling.

• involve retrogradationor re-ordering of the starch molecules and has been correlated with texture of various products.

DIFFERENCE IN PASTING PARAMETERS FOR CORN STARCH

AND POTATO STARCH

peak viscosity

Pasting temperature

breakdown

Peak temperature

Holding strength

Total setback

pasting curve for potato starch

peak viscosity

Pasting temperature

breakdown

Holding strength

Peak temperature

Total setback

pasting curve for corn starch

potato starch

corn starch

potato starch

corn starch

• pasting temperature of corn starch higher than potato starch. It is about 63.5°C for potato starch and about 75.05°C for cornstarch.

• larger granules gelatinizing at lower temperature and swelling more rapidly than small ones.

•peak viscosity for potato starch is 6069 cP and for corn starch is 2899cP.

•potato starch granules are much larger and, as a result, swell more easily.

• Large starch granules tend to build higher viscosity

•breakdown viscosity for cornstarch is lower than potato starch. for corn starch it is 1037 and for potato starch it is 4237.

•Viscosity break-down is the result of the molecule chain lengths being broken caused by heat.

•The larger size of granule,the less molecular bonding so it will breakdown faster.

• final viscosity of cornstarch is slightly higher than potato starch.

• due to higher amylose content in corn starch compared to potato starch.

• corn starch has a higher setback value compared to potato starch

• the amylose in corn starch reassociate more readily.

• retrogradation occurs due to association of linear amylose molecules, which can give rise to “setback”.