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Milk
Quality control parameter and Quality control
- Preservatives in milk
Preservatives is a substance which when added to food which when capable of inhibiting, retarding averting the process of fermentation acidification or other decomposition of food legally no preservatives of any salt is permitted in milk mean for human consumption. However the use of following preservatives must be observed.
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- Formaldehyde
Food samples taken for analysis are preserved with 0.1ml of formaldehyde for 25gm of sample it is not allowed for human consumption. Formaldehyde gives intake white coloration with concentrated sulfuric acid or concentrated HCL in the presence of oxidizing agent.
To about 10ml of milk in a test tube add 5ml of concentrated sulfuric acid carefully done beside the test tube so that it form a layer at the bottom with out mixing with the milk a violet or blue color at junction of 2 liquid indicate the presence of formalyhyde.
2. Boric acid and Borate
This are commonly used preservatives in food but not permitted in milk. There detection in milk is based on the fat that they turn turmeric paper red in an acidifying medium.
Immerse a strip of turmeric paper in a sample of milk previously acidified with HCL in the proposition of 7ml of concentrated HCL to each 100ml milk allows the paper to dry it self if boric acid or borate is present the paper will acquired a characteristic red color – turmeric paper is prepared by soaking the filter paper in a solution containing 100ml water in which 2.3gm of turmeric powder.
- Nutralizers in skim milk
The presence of Carbonate and bicarbonate(nutralizers) in milk can be detected by following test.
To about 5ml of milk in a test tube add 5ml of alcohol a few drops of 1% alcoholic solution of rosalic acid and mix if a carbonate is present a roes red color is appears where pure milk shows only a brownish coloration.The normal range of pH is 6.6 and 6.8 and the pH above 7 it indicated the presence of neutralizers.
- Detection of starch
About 5ml of milk in a test tube is bringing to boil by holding the tube over a flame allow cool to room temperature add a drops of 1% iodine solution, Presence of starch indicated by the appearance of a blue color which disappears when the sample is boiled and reappears on cooling.
- Detection of cane sugar
To about 15ml of milk in a test tube add 1ml of concentrated HCL and 0.1gm of resosinol and mix keep the tube boiling water bath for 5 minute in the presence of cane sugar a red color is produced.
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