Bovine Milk: A1 and A2 Beta Casein Milk Proteins and their Impact on Human Health: A Review

Abstract

Milk is the ideal food for all age groups of human being. Milk consists of 87 per cent water and the remaining 13 per cent is the milk sugar lactose, protein, fat, vitamins and minerals. Casein is the chief component of the milk proteins of which about 30 per cent is beta-casein. The major beta-casein variants are A1 and A2. Beta-casein consist a chain of 229 amino acids. Cows that produce milk contain proline amino acid are called as A2 cows. A2 milk is found basically in indigenous cows and buffaloes of India. Around 5,000 years ago, a mutation occurred in this proline amino acid, converting it to histidine amino acid at 67 th position. Cows that have this mutated beta casein protein are called A1 cows. Different mutations bovine beta casein produce 13 genetic variants and out of these A1 and A2 are the most common. A1 β-casein is enzymatically broken down in the intestine to produce beta-casmorphin-7 (β-CM-7) which is an opioid peptide similar to morphine. BCM-7 interacts with the human gastrointestinal tract, internal organs and brainstem. BCM-7 adversely affects the immune response and is also considered as a risk factor for chronic heart diseases (CHD) and juvenile insulin dependent type I diabetes mellitus (DM-I). The original beta casein protein in bovine milk was A2. A2 is more comparable to the human beta casein than A1 in terms of digestive breakdown. Indigenous dairy breeds of cow (Red Sindhi, Sahiwal, Tharparkar, Gir and Rathi) and buffalo produce A2 milk and India is endowed with rich A2 dairy animals.