A2 Milk and BCM-7 Peptide as Emerging Parameters of Milk Quality

Beta-casein makes up about 30% of the total protein contained in milk and can be present in cows' milk in two distinct forms (A1 or A2) or as a combination of the two. The only difference between these two variants of beta-casein (beta-CN) is a single amino acid substitution. This results in a different behavior of the protein upon enzymatic cleavage, following human consumption or due to microbial action. In most of the commercially available milk containing A1 or A1/A2 beta-CN variants, the beta-casomorphin-7 peptide (BCM-7) is released upon digestion and during cheese manufacturing/ripening, while this does not happen with A2 milk. BCM-7 is a known mu-opioid receptor agonist that may influence the gastro-intestinal physiology directly and may also exert effects elsewhere in the body, such as on the cardiovascular, neurological and endocrine systems. The present article is aimed at a revision of prior review papers on the topic, with a focus on the impact of ingestion of A1 beta-CN milk and A2 beta-CN milk on any health-related outcomes and on the impact of A1 or A2 beta-CN variant on technological properties of cows' milk. When systematic reviews were considered, it was possible to conclude that A2 beta-CN exerts beneficial effects at the gastrointestinal level compared with A1 beta-CN, but that there is no evidence of A1 beta-CN having negative effects on human health. Physicochemical differences among cows' milk containing either beta-CN A2 or beta-CN A1 and their effects on technological properties are discussed.