Effect of the bovine beta-lactoglobulin phenotype on the properties of beta-lactoglobulin, milk composition, and dairy products

The milk protein bovine beta-lactoglobulin exists in several genetic variants, the structure of each a consequence of one or more point mutations that alter the amino acid sequence. The A variant of beta-lactoglobulin differs from the B variant (Gly(64)Asp and Ala(118)Val) and is associated with a major increase in beta-lactoglobulin concentration and a number of other compositional differences in the milk. Such changes are less marked, or unreported, for the other known variants. The denaturation temperatures of the A, B, and C (Gln(59)His) variant proteins at neutral pH follow the order: C > A > B. However, the effects of heat on beta-lactoglobulin-containing materials, such as whey protein concentrate, whey protein isolate, and concentrated milk, are influenced by the different ratios of the various proteins present as well as the intrinsic properties of the beta-lactoglobulins. Although the differences in the effects of the variants measured in the laboratory appear to be relatively slight, the technical and economic impacts can be much greater.