DENATURATION OF THE WHEY PROTEINS IN HEATED MILK AND THEIR INCORPORATION INTO CHEDDAR CHEESE

Gel permeation FPLC (Fast protein liquid chromatography) was used to e xamine the effect of different heat treatments on the level of denatur ation of four whey protein fractions, namely immunoglobulins, serum al bumin/lactoferrin, beta-lactoglobulin and alpha-lactalbumin. As the se verity of heating increased, each of the whey proteins showed a loss o f solubility at pH 4.6,and the de crease in their concentrations in ac id filtrate, as determined by gel permeation FPLC, was taken as a meas ure of the levels of irreversible denaturation. The extent of denatura tion of the total whey protein increased with temperature between 72 a nd 140-degrees-C and with holding times between 15 s and 5 min. At hol ding times of 1 min, the immunoglobulin and serum albumin fractions we re most affected at temperatures between 72 and 90-degrees-C, whereas beta-lactoglobulin was most affected over the range 72 to 120-degrees- C, and alpha-lactalbumin at temperatures between 72 and 140-degrees-C. On adjusting the pH of milk and then heating at 90-degrees-C for 30 s , the levels of denaturation of beta-lactoglobulin, alpha-lactalbumin and total whey protein increased considerably as the pH was raised fro m about 6.5 to 9.1. There was a close correlation between the levels o f denaturation of beta-lactoglobulin and alpha-lactalbumin and the amo unts of these proteins retained in the curd during the pilot-scale pro duction of Cheddar cheese. Results indicate that gel permeation FPLC c ould be used to examine levels of denaturation of the whey proteins in industrial heating equipment, and their recovery in the curd during c heese manufacture.