Chapter 30 - Harnessing potential of A2 milk in India: an overview

Abstract

Caseins constitute the main component of milk proteins and amongst these beta casein is the second largest contributor. Beta casein is the resource for different bioactive peptides which are generated during the course of digestion of beta casein. These bioactive peptides bind to receptors and initiate/affect different molecular pathways. The release of specific type of peptide is determined by the sequence of the native protein. Amongst the 15 different variants of beta casein identified to date, A1 and A2 hold impotence due to their association with human health. These two variants differ at one amino acid at 67th position (proline-A2 to histidine-A1) of the 229 amino acid chain of beta casein. Digestion of A1 milk (having A1 variant of beta casein) results in the generation of beta-casomorphin 7 (BCM-7) bioactive peptide while in case A2 milk, BCM-9 is generated. BCM-7 has comparatively higher affinity for mu and delta opioid receptors distributed over gastrointestinal tract, various cells and tissue types in central nervous system. Moreover it is more resistant to the action of gastrointestinal enzymes, has a longer half-life and also biologically very potent. Activation of opioid receptors upon binding of BCM-7 can affect various intracellular pathways which subsequently can result in different health disorder. Different epidemiological and experimental evidences suggest BCM-7 generated from A1 type milk to be a risk factor for different diseases like type 1 diabetes or coronary heart disease or autism etc., however, the association of intake of A1 type milk with different human diseases is still not well understood and needs further studies. Until that time it is very pertinent to know the frequency profile of beta casein variants in animals being major contributors of milk. The screening for the status of A2/A1 allele of beta casein in different species or breeds in India revealed the frequency of favorable A2 allele across Indian native cattle breeds is 0.95 whereas for crossbred and taurine breeds it is nearly 0.70. Even the breeding bulls being used for artificial insemination, the frequency of A2 allele is 0.70. This indicates our native cattle breeds as well as crossbred population could be the best resource to meet the global demands for A2 milk.