The five principal protein groups in milk fall into two major categories by their chemical behavior towards acid or rennet enzyme. Caseins are precipitated from fluid milk at pH 4.6 and 20 degree Celsius or by the addition of rennet without pH change. Mastitis will lower the proportion of casein in total proteins of milk drastically. Proteins are composed of a chain of amino acids with very different physical and chemical properties, which explains the different effects of the different proteins in human digestion and metabolism. The first 8 amino acids are essential in human nutrition.
Many milk proteins have genetic variants which have been identified by letters of the alphabet.
Caseins consist of alpha, beta and kappa types with about 27 genetic variants from A to E for each. Unless there are other reasons for milking goats, a justification for their keeping may be questioned. Low amounts also have shorter cheese coagulation time, less curd firmness, less cheese yield and weaker resistance to heat treatments, which can also be related to digestibility in human nutrition. Recent advances in nutrient requirements of goats. Goats, New Delhi, India, ICAR, Ahrne, L., Bjoerck, L., Raznikiewicz, T. and Claesson, O. 1980.