Proteolytic pathways in bovine milk containing β-CN A1 or A2

This study examined how the genetic variants A1 and A2 of β-casein (β-CN) affect proteolytic pathways in bovine milk, specifically examining how the amino acid substitution of histidine (A1) with proline (A2) influences the hydrolysis of milk proteins by plasmin. Raw milk samples from seven cows were collected on three occasions, and their proteolysis was analysed using urea-PAGE and UPLC-UV. Peptides released by proteolysis were identified using LC-MS. Milk with the A2A2 genotype exhibited higher plasmin activity, and caseins were more susceptible to hydrolysis by plasmin than those in A1A1 milk. Peptides from β-CN His₆₇-Asn₆₈ cleavage were present in A1A1 milk, but no peptides were linked to cleavage sites 66–67 or 67–68 in A2A2 milk. This indicates that a single amino acid difference can significantly influence proteolytic pathways, which may affect dairy processes and product quality.