Heat-induced interactions and gelation of mixtures of bovine beta-lactoglobulin and serum albumin

The storage modulus, G', and aggregation of beta-lactoglobulin AB and bovine serum albumin (BSA) were measured during 60 min of heating at 70 or 75 degrees C in a buffer simulating the whey protein concentrate environment. BSA formed stiffer gels than beta-lactoglobulin and also aggregated (shown by loss of native protein by PAGE) and polymerized (shown by loss of residual monomeric protein by SDS-PAGE) more rapidly than beta-lactoglobulin. Both BSA and beta-lactoglobulin formed heat-induced hydrophobically bonded aggregates which may have been intermediates in the transformation of the native proteins into the disulfide-bonded gel networks. The gelation temperature (the temperature at which an appreciable increase in G' occurred during heating at 1 degrees C/min) of mixtures of BSA and beta-lactoglobulin at a total protein concentration of 10% (w/v) increased from similar to 72 degrees C, for BSA alone, to similar to 84 degrees C, for beta-lactoglobulin alone. When protein solutions were heated, BSA solutions formed stiffer gels at lower concentrations and at lower temperatures. When 10% mixtures of the two proteins were heated at 75 degrees C, the gelling behavior of the mixture was more akin to that of BSA when BSA was the major constituent in the mixture and vice versa. The results are consistent with the formation of intertwined and commingled homopolymers of BSA and beta-lactoglobulin together with some heteropolymers, The proportion of homo- and heteropolymers in each mixture is probably dependent on the heating temperature and the composition of the mixture.