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

Gel permeation FPLC (Fast protein liquid chromatography) was used to examine the effect of different heat treatments on the level of denaturation of four whey protein fractions, namely immunoglobulins, serum albumin/lactoferrin, beta-lactoglobulin and alpha-lactalbumin. As the severity of heating increased, each of the whey proteins showed a loss of solubility at pH 4.6,and the de crease in their concentrations in acid filtrate, as determined by gel permeation FPLC, was taken as a measure of the levels of irreversible denaturation. The extent of denaturation of the total whey protein increased with temperature between 72 and 140-degrees-C and with holding times between 15 s and 5 min. At holding times of 1 min, the immunoglobulin and serum albumin fractions were 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 from about 6.5 to 9.1. There was a close correlation between the levels of denaturation of beta-lactoglobulin and alpha-lactalbumin and the amounts of these proteins retained in the curd during the pilot-scale production of Cheddar cheese. Results indicate that gel permeation FPLC could be used to examine levels of denaturation of the whey proteins in industrial heating equipment, and their recovery in the curd during cheese manufacture.