Influence of minor β-CN genotypes on coagulation properties and proteolytic pathways of bovine milk

Numerous studies have examined the effects of the two most common β-casein (β-CN) genetic variants, A1 and A2, on the physicochemical and functional properties of bovine milk. However, relatively minor variants of this protein such as B and I remain under-researched. This study collected milk with four β-CN genotypes, A1B, A2B, A1I, and A2I, across three collection occasions to investigate their functional and proteolytic properties. Milk of the B variant exhibited similar behaviour to A1 regarding rennet and acid coagulation properties, while I was similar to A2. Furthermore, the Glu₁₂₁-Arg₁₂₂ and Arg₁₂₂-Gln₁₂₃ bonds in the β-CN B variant were more sensitive to plasmin-derived proteolysis than Ser₁₂₂ in other variants, leading to more peptides from cleavage at Arg₁₂₂-related sites. These findings support grouping genotypes based on the amino acid (AA) at position 67, as variants sharing the same AA at this position exhibit similar processability, while also highlighting the significant impact of AA at position 122 for proteolysis in milk or dairy products.