Aggregation and gelation of bovine beta-lactoglobulin, alpha-lactalbumin, and serum albumin

Solutions (10% w/v) of bovine beta-lactoglobulin, alpha-lactalbumin, and serum albumin (BSA), in a buffer simulating the whey protein concentrate environment, were heated to 75 degrees C and held for 60 min. Aggregation and gelation were measured using native- and sodium dodecyl sulfate polyacrylamide gel electrophoresis on natural and reduced samples, and dynamic oscillation rheology, respectively. BSA formed stiffer gels than beta-lactoglobulin whereas alpha-lactalbumin did not gel under these conditions. Heating 10% mixtures of beta-lactoglobulin and BSA showed that the gelling behavior of the mixture was similar to that of BSA when BSA was the major protein in the mixture and vice versa. In contrast, the gelling behavior of a mixture beta-lactoglobulin and alpha-lactalbumin was dominated by beta-lactoglobulin. Both beta-lactoglobulin and BSA formed hydrophobically bonded aggregates and disulfide-bonded polymers, but alpha-lactalbumin did not form aggregates under the conditions used. However, alpha-lactalbumin aggregated rapidly when heated in the presence of beta-lactoglobulin. These results indicate that the protein aggregates forming the gel network in heated BSA and beta-lactoglobulin solutions are different than those in mixtures of beta-lactoglobulin and alpha-lactalbumin.