Title: SAMPLING OF MILK AND MILK PRODUCTS

Quantity of sample to be collected for analysis
Product	Approximate quantity
Milk	250 ml
Ghee	150g
Butter	150g
Khoa	250g
Dahi	200g
Cream	250g
Ice-cream	300g

It is essential to draw a rep­resentative sample of milk and milk pro­ducts for chemical and microbiological examination to ensure that the product meets the prescribed standards of quality and acceptance. Analysis of milk and milk pro­ducts is carried out for de­termining the various milk constituents and studying its physico-chemical properties. Accurate sampling is most important in all analysis. Seri­ous errors in experimental re­sults are caused due to improper sampling procedures. A sample must be a proper rep­resentative of the lot from which it is collected. Hence, thorough mixing of milk is a must before the collection of a sample. However, vigorous shaking must be avoided as this will cause churning of fat and foaming of milk, etc. A sample must have enough quantity for all types of analysis as given in table for milk and milk products.

Aim

To become familiar with the different procedures to be followed in collecting samples of milk and milk products for analysis.

Procedure

A -Sampling of milk

(i) Sampling from individual container

·         Pour milk from one con­tainer to another 3 or 4 times.

·         When this is not possible, thoroughly mix the milk with a plunger, so that any milk fat adhering to the inner side of the can gets well mixed with the re­mainder of the milk.

·         Collect the sample immediately with a dipper from several spots.

(ii) Sample from individual animal milk

           ·           When the sample of milk is collected from individual animals ensure that the last strippings are drawn from the udder.

           ·           The entire amount of milk is mixed thoroughly the sample col­lected with the help of a dip­per.

           ·           For normal laboratory analysis, about 250 to 500 ml of milk may be collecte­d in clean, dry sample bottles.

 (iii) Sampling from several containers:

Pour all the milk from all the containers into a single vat.

           ·           Mix thoroughly with the help of a plunger.

           ·           Collect the sample with a dipper from separate places.

           ·           If pouring of milk in a vat is not possible then distri­bute milk as equally as possible amongst all the containers.

           ·           Thoroughly mix the milk of all the containers.

           ·           Collect a proportionate volume of milk from each container with a dipper in another vessel.

           ·           After thorough mixing, collect the final sample.

(iv) Sampling from milk storage tanks and road or rail milk tanker

           ·           Thoroughly mix the milk in the tank using a mechanical agitator or a long plunger.

           ·           Collect sample either through the sampling cock or using a dipper or opening the manhole.

(v) Sampling bulk units

           ·           When milk of uniform qual­ity is supplied in bulk units e.g. cans, storage tanks, etc., the number of random units to be drawn shall be as follows:

Total No. of units	No. of units to be selected
1	1
2-5	2
6-20	3
21-60	4
61-100	5
over 100	5 plus one for each additi­onal l00 units or fraction thereof.

(vi) Composite milk samples fat and SNF test

           ·           The suppliers of milk are normally paid on the basis of fat and SNF content of milk. Daily analysis of milk for fat and SNF is time-consuming and quite expensive. In such a case, composite samples of the suppliers' milk are ta­ken.

           ·           The volume of the indi­vidual composite sample should not be less than 150 ml.

           ·           The composite milk sample should be collected during the agreed period by placing into the composite sample bottle, a representa­tive sample proportionate to the amount of milk supplied each day.

           ·           The composite sample should be preserved with 0.1 ml addition of 36% Formaldehyde (Formalin) for every 25 ml of milk.

           ·           The bottle should be tightly stoppered to prevent evaporation and kept away from light.

           ·            It should be tested on the same day as the last portion of milk is collected into the sample bottle.

           ·            After each addition of milk the contents of the sample bottle ate mixed by gentle rotation of the bottle

Treatment of milk on arrival at the laboratory before analysis

           ·           Warm the sample in the bottle to about 40°C in a bath and mix thoroughly. Cool to 26°-28°C. Leave aside the sample for about 4 minutes. After that mix the sample by inverting the bottle 3—4 times and start analysis

B- Sampling of cream

           ·           Mix fresh cream in the can with the help of a plunger or by using a mechanical agitator for not less than 10 minutes. Aged cream may be warmed to 40°C before mixing.

           ·           Collect the sample with the help of a dipper or through a sample cork.

C- Sampling of khoa, chhana and burfi

           ·           Keep the product on a clean flat surface over a        butter paper.

           ·           Remove the top surface of the product by scrap­ping with the help of a, knife or spatula.

           ·           Insert the sampler in the product and rotate it.

           ·           Remove the sampler and transfer the product in a sample bottle.

           ·           Take samples of these products from several places of the same lot and mix to obtain a repre­sentative sample.

D- Sampling of butter

           ·           Remove 3 or 4 cores with a butter trier from various parts of the butter sample.

           ·           Combine the collected cores of butter samples in a bottle with wide mouth.

           ·           Melt the product at 40°C in a water bath by a swirl­ing action and collect the sample.

E- Sampling of Ice-cream

           ·           Take the cup of ice-cream and remove a core from the top.

           ·           Transfer the product to a bottle with a wide mouth.

           ·           Keep the bottle in a water bath at 40°C.

           ·           Mix the product by shaking the bottle slowly.

           ·           Collect the sample after removing the foam completely.

Precautions

·         The sample bottle used should be wide mouthed with sloping sides and should have well fitting caps.

·          The sample bottle should be of such a size that when the required quantity of sample is put into it there should not be much space after putting the stopper. Only rubber stopper should be properly labelled for its content.

·          When mercuric chloride is used for freezing point determination the bottle should be labelled clearly as “Poison”. Mer­curic chloride is to be added at 0.5 gm for each 250 ml milk

           ·           Avoid excessive agitation of milk.

           ·           Prevent contamination of sterilized apparatus.

           ·           Avoid over agitation of cream as this will cause churning of cream.

           ·           When a sample is collected for bacteriological analysis, ensure that the equipment used has been properly sterilized and the sampling is carried out under strict aseptic conditions. Follow the instructions given.

           ·           If small clots or lumps are observed in the sample which cannot be dispersed, a few drops of liquor ammonia may be used during mixing/homogenisation.

           ·           If even after mixing /homogenisation the sample shows lumps or clots or droplets of oil are visible suggestive of curdling /splitting of milk, the sample should be deemed unfit for analysis and rejected.