Milk is recognized as a nearly complete food in India and globally. Milk and milk products have a special significance in human diets. Cow milk on an average contains 87-88 per cent water and 12 to 13 per cent solids that include lactose (4.8%), fat (3.9%), protein (3.2%) and minerals (0.7%). About 82% of the total milk protein in cow milk is casein composed of three main fractions viz., Alpha (48%), Beta (39%) and Kappa casein (13%). The Beta casein has 13 known variants out of which two variants A1 and A2 are most common. Beta casein has 209 amino acids. A2 cow milk variant at position 67 in the carbon chain carries proline whereas A1 variant at position 67 has histidine. A1 protein is the result of a natural mutation of A2 protein which occurred more than 1000 years ago.
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