What is A2 milk?
The major difference between A1 and A2 beta-casein proteins is a single amino acid at position 67 in a strand of 209 amino acids.
Milk has two types of protein: casein and whey protein. Casein protein is the largest group of proteins in milk, making up 80% of the total protein in milk. The casein protein in milk consists of several types of casein forms and beta-casein is the second-largest component in this group.
The two most common forms of beta-casein are A1 and A2 beta-casein. A1 beta-casein in cow’s milk is different to other mammalian beta-caseins, because of the amino acid histidine at position 67.
A2 beta-casein has a proline amino acid at position 67. Human milk, goat milk, sheep milk and other species’ milk contain beta-casein which is A2-like, because they have proline at the equivalent position in their beta-casein chains.