Proportions of A1, A2, B and C β-casein protein variants in retail milk in the UK

► We report new data on the key β-casein variant proteins in UK retail milk. ► A2 β-casein is the most abundant variant protein. ► Proportion of A2 β-casein is higher and A1 lower than early studies would predict. The A1 variant protein of the β-casein family has been implicated in various disease states although much evidence is weak or contradictory. The primary objective was to measure, for the first time, the proportions of the key β-casein variant proteins in UK retail milk over the course of one year. In total, 55 samples of semi-skimmed milk were purchased from five supermarkets over the course of a year and the proportions of the A1, A2, B and C casein variant proteins were measured, using high resolution HPLC–MS. The results showed that β-casein in UK retail milk comprises approximately 0.58, 0.31, 0.07 and 0.03 A2, A1, B and C protein variants, respectively. The proportion of A2 is higher than some early studies would predict although the reasons for this and any implications for health are unclear.