Heat-induced gelation of the bovine whey proteins [serum albumin (BSA), P-lactoglobulin (p-Lg) and a-lactalbumin (a-La)] has been studied individually and in mixture at different conditions by a dynamic rheological method. Values in the shear stiffness modulus (lG*/) appeared on heating at low protein concentration for BSA (-2%) and at intermediate concentration for p-Lg (-5%). a-La did not form a heat-induced gel of concentrations up to 20% (w/v). The ratio of viscous to elastic properties (loss factor) at maximum possible measuring temperature was below 0.07 for the BSA gels and 0.1-0.3 for the p-Lg gels. The temperature of gelation was highly dependent on pH. In mixture one protein could not be exchange for another without changing the gelation behavior of the mixture.

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SummaryA procedure is described for the determination of the lipolytic activity in milk using tributyrate as substrate. The method is based on the titration of liberated butyric acid in a diethyl ether: light petroleum (2·75:1, v/v) extract of the incubation mixture. Some of the fundamental factors involved in the procedure are discussed.