THERMAL AGGREGATION OF WHEY-PROTEIN ISOLATE CONTAINING MICROPARTICULATED OR HYDROLYZED WHEY PROTEINS

Thermal aggregation from 25 to 97 degrees C (0.8 degrees C/min heating rate) of diluted whey protein isolate (WPI) containing microparticula ted WPI (mu WPI) or specific WPI tryptic hydrolysate was studied at pH 6.0 using a spectrophotometric method. Mixed WPI solutions containing above 3.75% mu WPI displayed faster thermal aggregation at lower heat ing temperatures of protein species than the control WPI solutions (no mu WPI added), with a shift of aggregation mechanism from predominant ly homogeneous to biphasic. Interactions between whey proteins and sol uble/insoluble whey protein microparticles were thought to be at the o rigin of the shift. Results also showed that the presence of 20-40% WP I tryptic hydrolysate into the WPI solutions improved whey protein the rmal aggregation at pH 6.0. Such a result could not be ascribed only t o protein-peptide interactions because hydrolysate promoted an initial acidification of WPI solutions from 6.9 to 5.4 (20% hydrolysate added ) or to 4.6 (20% hydrolysate added), which contributed to whey protein isoelectric precipitation and formation of whey protein aggregates.