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QUALITY CONTROLOF MILK AND MILK

PRODUCTS

PRESENTED BYHARNEETKAUR

L-2011-V-87-M

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WHAT IS QUALITY CONTROL

MEANS??

Quality control or quality assurance concerns theactivity or procedure that ensures themaintenance and continuity of the specificationand standards of the products within theprescribed tolerance limits during stage ofhandling ,processing, preparation, packaging,presentation ,storage and distribution.

It ensures that desirable characteristics areretained during these operations and remainunalter until the product reaches the consumer.

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,quality control of milk and milk product s isclassified as:

1) compositional quality

2)microbial quality

COMPOSITION QUALITY:

Composition of milk vareies with breed of the milchanimals ,species ,stage of lactation, feed ,seasondisease conditions of udder.

Clincal and subclinical mastitis causes a fall inlactose and potassium concentrations and anincrease in those of sodium chloride and proteinsderived from the blood serum.

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ACIDITY 0.13-0.14% O.14%-0.15%

PH 6.4-6.6 6.7-6.8

SPECIFICGRAVITY 1.028-1.030 1.030-1.032

FREEZINGPOINT

0.547C 0.549C

COLOUR YELLOWISHCREAMYWHITE

CREAMYWHITE

FLAVOUR SWEET TASTE SWEET TASTE

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ADULTERARTION IN MILK AND

METHODS OF DETECTION

Adulterations of milk is due to rapid growth of population andurbanization which lead to shortage of milk is major cause ofadulteration.

This malpractice is punishable under section 420 of Indian Penal Code.

BUREAU OF INDIAN STANDARD has recommended a number of platformtests for detection of changes caused by microbes in milk:

1) Organoleptic tests

Test for colour :normal milk has yellow or white colour.occurence of other

colour is indicative of abnormality eg blue colour by Pseudomoassyncyanea , red by Micrococcus roseus,yellow by Sarcina luteaandblack by P.nigrificans.

Flavour:milk sample with foul or abnormal smelll like acid or sour ,rancidputrid etc like fishy and phemolic flavours due to P.fragi, P.fluorescens.

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Taste: bitter taste in milk may be .cause ofS.liquefaciens.

2)Clot on boiling test (COB): tit gives an indication about the susceptibilitymilk to heat processing and its keeping quality.

Milk having high acidity gets coagulated on boiling for this test we take 5mlof milk in a test tube and keeping in water bath at boiling temperature o5 minutes.

3)Sediment test : this test is performed to judge the cleanliness of milk.Milk ifiltered or centrifuged and checked for sediment. A good quality milk

shows no visible dirt whereas poor quality milk shows a dark or blackishdeposit on filter pad.

4)Alcohol test : the test is used to assess the effect of high heat treatment onmilk.a positive test indicates flakes formation when alcohol is added intube having 5ml of milk. SUCH MILK SHOULD NOT BE USED FORMANUFACTURE OF CONCENTRATED MILK, MILK POWDER.

5) pH determination: PH value of normal milk is 6.6-6.8,whereas milk frominfected udder is alkaline.pH is determined by using ph meter, phindicator strips of ph indicators solution (bromocresol purple and

bromothymol blue.)

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After soldification of agar, the plates are incubated at a specifictemperature and for a suitable period of time depending on the type ofbacteria being counted.

The number is expressed as colonies forming units of theproduct.(cfu/ml)

B) membrane filtration technique: it is generally used for countingviable bacteria in milk. This involves filtration of samples through amembrane filter which is followed by transferring the filter on padsoaked in nutrient medium.

It is generally used for enumeration of coliforms in raw and pasteurizedmilk.

C)Microscopic methods:

a)Direct microscopic count(DMC): it is used for enumeration of both viable

and non- viable organisms in milk. This involves examining fixed andstained smears of known volume of milk and milk products undr acompound microscope

A small quantity of the sample is smeared over an outlines area of 1 cmsquare(100 m/m2).the smear is air dried fixed stained with Newmansstain .total number of organisms per ml are then calculated bymultiplying the average number of organisms per field.

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B) fluorescent staining: this method is used to enumerate bacteria inwet and dried preparations of milk and other foods.

In this technique produces better contrast between organisms and thebackground.the fluorescent stains commonly used are fluorescein

isothiocyanate ,rhodamine B.

C) flow cytometry:it is an opticallybased technique which can providecelll by cell anin this cell suspensions are treated with fluorescent stains,passed through a laser beam .

Light scattering and fluorescent parameters are determined.

D) Direct epifluorescent filter technique(DEFT):this is one of the directmethods for enumeration of bacteria in milk and milk products.

the miccroorganisms are recovered from the sample by the use of

membrane filtration and the cells are stained with fluorescent dye andcounted under a fluorescent microscope.

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2. METHODS FOR DETECTION OF

SELECTED SPECIES OF ORGANISMS.

i) Radiometric methods:it is based on the release of radioactivelylabelled 14 co2, after utilization of the labelled nutrients in the mediumby the microorganisms.

ii)immunological techniques: specific antibodies are used for detection ofselected foodborne pathogenic or spoilage micro organism.

For we used both polyclonal and monoclonal antibodies.

iii) DNA based technique: it uses gene probes and polymerase chainreaction for detection of specific organisms.

2) INDIRECT TESTS

i) Dye reduction testsIt is based on the bacterial dehydrogenase activity.

Dehydrogenases are enzymes which transfer hydrogen from a substrateto biological acceptor this results in change in colour of dyes likemethylene blue and rezurin. which depend on enzyme activity produdedby number of bacteria.

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ii) Sensory evaluation: the smell and taste test for assessing the qualityof milk.

iii) Titratable acidity: natural acidity in milk is due to the presence ofits constituents like casein , acid phosphates, citrates etc.

Enzymatic breakdown of lactose by microorganisms leads to productionof lactic acid .this results in increase acidity.

It is measured by determining the amount of alkali required to changethe ph of milk which is indicated by phenolphthalein in milk.

Methylene blue reduction test (MBRT):add 1 ml of methylene blue to 10ml milk in a test tube and incubate at 37C.

Keep negative control with 10ml boiled milk in a separate test tube towhich 1 ml of methylene blue is added.

The length of time taken by milk to decolourise methylene blue is afairly good measure of its bacterial content and keeping quality.