Analysis of milk

Composition of milk

Buffalo milk : high fat content (7.44%)Cow milk : low fat content ( 3.66%)

TYPES OF MILKo Standardized milk: buffalo milk & skimmed milk ( fat -4.5% & SNF is 8.5%)

o Whole milk: 3.25% milk fat & 8.25% milk solids (50% of its calories 4m fat)

o Reduced-fat milk (2%): This milk contains 2% milk fat (35% of its calories)

o Low-fat milk (1%): 23% of its calories from fat

o Skimmed milk/non-fat milk: NMT 0.5% milk fat 5% of its calories from fat. Skimmed milk has about half the calories of whole milk.

o Pasteurized : milk kill bacteria(not spores)o Pasteurized milk will keep fresh for 2-3 days in a fridge

o Unpasteurized - raw or untreated milko It is recommended that babies, young children, the

elderly, pregnant women and anyone with an impaired immune system should avoid drinking unpasteurized milk.

630C for 30min 720C For 15sec

o Long - life - milk pasteurized & homogenized and then kept at a high temp for destroy bacteria.

odd burnt caramel flavour

stored for 1 week

o UHT( ultra-heat treatment) milk heated at high temp (1320C / 2700F)

Stored for upto 3 months

o Dried Milk: in powdered form.

o Evaporated : homogenized milk with considerably reduced water content

o Condensed milk :simply evaporated milk to which sugar has been added to thicken and sweeten it. It is mainly used for making desserts and sweets.

Preparation of sample

o Warm the sample to 37 0 – 40 0 C by transferring it to the

beaker & keep it in a water bath maintained at 400 - 450C

o Stir slowly for proper homogenisation. Mix sample thoroughly by pouring back into the bottle, mixing to dislodge any residual fat sticking to the sides and pour it back in the beaker.

o Allow the sample to come to room temperature

(26 0 - 28 0 C) and withdraw immediately for analysis.

SPECIFICGRAVITYo LACTOMETER

o 1.025-1.035 (250C-350C)

o After 12hr of milking rise 0.0013

DETERMINATION OF PH

o PH Meter

o Calibrate the PH Meter

o Avg . PH 6.6

o Due to lactic acid

Determination of total solid:

RICHMOND’S Formula For Total Solids :

For cow milk 0.66

Where,

D = Density

F = % Fat

T=0.25D+1.22F+0.72

DETERMINATION OF CHLORIDE CONTENT

10 ml milk + 40 ml water

add 10 drops of pot.chromate

Titrate with 0.1 N AgN03

1 ml of o.1 N AgN03 equivalent to 3.55mg of Cl-

Brick red ppt

INDICATIVE OF DISEASED STATE OF ANIMAL

TITRABLE ACIDITY

10 ml milk + 1 ml phnolpthalein indicator

Titrate with 0.1N NaOH

1 ml 0.1 N NaOH ≈ 0.009 g of lactic acid

Determination of Fat in Milk

Gerber Method:

Principle:o milk +H2S04 + iso-amyl

alcohol o permitting dissoln of

the protein and release of fat.

o The tubes are centrifuged and the fat rising into the calibrated part of the tube is measured as percentage of the fat content of the milk sample

Procedure:

10 ml of H2S04 into a butyrometer tube & Mix the milk sample

Add 1 ml of Amyl alcohol,close with a lock stopper

shake until homogeneous soln.Keep in a water

bath for 5 min at 65o C

centrifuge for 4 min. at 1100 rpm.

Remove the butyrometer tubes and place in water bath for 5 min.at 650C.

Read the percentage of fat

Werner Schmidt Method(by Acid Digestion Method):

PRINCIPLE:

Milk proteins are digested with conc. HCl

Liberated fat is extracted with alcohol, ethyl ether & petroleum ether

Ethers are evaporated

Residue left behind is weighed to calculate the fat content.

10 g milk+10 ml conc.HCl

stir with a glass rod until the contents turn dark brown

Mojonnier fat extraction flask

10 ml of C2H50H+ 25 ml of ethyl ether

25 ml of petroleum ether Shake vigorously for 1 min

Centrifuge Mojonnier flask at about 600 rpm

heat on a Bunsen burner

cool to room temp

Shake vigorously for 1 min

Decant the ether soln

Repeat extraction

Evaporate the solvent

Dry the fat in oven

Weigh

Calculation:

100 (W1 - W2)

Fat, percent w/w ----------------------

W3Where• W1 = Wt in g of contents in the flask before removal of fat.

• W2 = Wt in g of contents in the flask after removal of fat

• W3 = Wt in g of material taken for the test.

Detection of Adulterants in Milk

Detection of Cane Sugar in Milk

Modified Seliwanoff Method:

PRINCIPLE:

Fructose + resorcinol in HCl red colour

procedure

Procedure:

milk + conc. HCl filter

1 ml filtered milk serum & 5 ml modified resorcinol - HCl reagent

Withdraw the tube &observe the colour

red colour

std for 10 min

water bath for exactly 1 min

Test for QAC (Detergents)o To a centrifuge tube add 1 ml milk, 5 ml water, 1 ml EOSIN

soln & 0.2 ml buffer and shake hard for 10 sec.

o Centrifuge for 5 min at 3200 rpm.

o If QAC is present the bottom layer assumes a red or pink colour.

o Samples containing 1 mg / kg of QAC show a faint pink

o If the colour is deep pink or red, the amt of QAC can be approx. determined by titration with a std anionic detergent soln

Detection of added Urea in Milk

o 5 ml of milk is mixed with 5 ml of 1.6 % of p –Dimethyl amino benzaldehyde (DMAB) is added observed in milk containing added urea.

o The control (normal milk) shows a slight yellow

colour due to presence of natural urea.o :

Distinct yellow colour

Estimation of Urea in Milk

Prepn of standard Curve:o Pipette 5 ml std solns into 25 ml T.T Add 5 ml

DMAB soln to each.

o Prepare reagent blank of 5 ml buffer and 5 ml DMAB soln. Shake tubes thoroughly and let stand for 10min.

o Read a@420 nm

Preparation of sample:o 10 ml of milk sample add 10 ml of Trichloro

acetic acid (TCA) to ppt the proteins and filtered.

o 5 ml of filtrate + 5 ml of DMABo The optical density of the yellow colour is

measured @ 420 nm. o From standard curve the amount of urea in

milk is calculated.

70 mg per 100 ml (700 ppm)

Detection of preservatives

Hehner’s Test (HCHO):

2 ml milk in T.T

2 ml of 90 % H2SO4 traces of FeCl3

Formaldehyde

purple color ring at the junction

Test for presence of Salicylic acid:

50ml milk + 5 ml of dil.HCl + 50 ml ether

Wash ether layer with water

evaporate ether

1 drop of 0.5 % (v/v) FeCl3

Violet colour

Test for presence of H2O2

Milk + conc.HCl

Mix well

drop of HCHO soln

600C

place starch-Iodine paper into soln

oxidesation of iodine

BLUE COLOR

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Normal flora of milk:

Bacteriological Examination of Milk

oEnterococcus faecalisoStreptoccus lactusoLactobacillus sp.o Candida albicans (yogurt)

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Determination of viable bacterial count :

The pour plate method: After preparation of 10 fold serial dilution from

the milk sample with ringer solution

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Using 10 fold serial dilution method

Viable Bacterial Count

9 ml Saline1 2 3Milk sample

1 ml milk 1 ml 1 ml

1/101/10 x 1/10

1/1001/100 x 1/10

1/1000

1 ml 1 ml 1 mlMelted NA

1 2 3

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Results:

Dilution factor 1 2 3 X X . y

10 x1 X1.y1

102 x2 X2.y2

103x3 X3.y3

Viable Bacterial Count

No. of colonies per plateY

No. of cells per 1 ml = X1.y1 + X2.y2 + X3.y3

3

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Results:

o Permissible number of bacterial flora in pasteurized milk is 5 x 104 cfu/ml

o Permissible number of bacterial flora in long life milk is 10 cfu/ml

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Methylene Blue Reduction Test:

o Increasing the number of bacterial flora will reduce the colour of methylene blue more rapidly due to increasing consumption of oxygen.

o i.e: The speed of reduction of methylene blue colour is directly proportional to the number of bacteria present in milk sample.

determine quality of the milk

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Results:

The shorter the decolorization time, the higher the number of bacterial flora present in milk, and the poor quality of milk

Decolorization time Result

30 min – 2 hrs Poor quality

2 – 6 hrs fair quality

6 – 8 hrs good quality

Over 8 hrs excellent quality

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Test for coliforms:

o Done by inoculation of MacConkey’s broth with 0.1 ml of milk sample.

o Examine for the production of acid detected by changing the color of the medium from purple to yellow.

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