DENATURATION, AGGREGATION AND HEAT-STABILITY OF MILK PROTEIN DURING THE MANUFACTURE OF SKIM MILK POWDER

The effect of preheat treatment, evaporation and drying in a commercial plant on the denaturation of beta-lactoglobulin and alpha-lactalbumin, their incorporation into the casein micelle and the heat stability characteristics of the milks and powders were determined. Preheat treatments between 110-degrees-C for 2 min and 120-degrees-C for 3 min denatured between 80 and 91% of beta-lactoglobulin and between 33 and 45% of alpha-lactalbumin. Evaporation increased the extent of denaturation but spray drying did not increase it further. The incorporation of alpha-lactalbumin and beta-lactoglobulin into the micelles was markedly less than the amount that denatured and was not a constant ratio to it. Heat coagulation times at 140-degrees-C of milks, concentrates and powders diluted to the original milk concentration were measured as a function of pH. In general, the greater the collective heat treatment, the shorter the time required to achieve coagulation. Spray drying shifted the peak positions in the pH-heat coagulation time profiles. In contrast, heat coagulation times (measured at 120-degrees-C) of concentrates and powders diluted to 20% total solids content increased with the severity of the preheat treatment. Surprisingly, spray drying markedly increased the heat coagulation times of the diluted concentrates.