Thermal Aggregation of Whey Protein Isolate Containing Microparticulated or Hydrolyzed Whey Proteins

Thermal aggregation from 25 to 97 °C (0.8 °C/min heating rate) of diluted whey protein isolate (WPI) containing microparticulated WPI (μWPI) or specific WPI tryptic hydrolysate was studied at pH 6.0 using a spectrophotometric method. Mixed WPI solutions containing above 3.75% μWPI displayed faster thermal aggregation at lower heating temperatures of protein species than the control WPI solutions (no μWPI added), with a shift of aggregation mechanism from predominantly homogeneous to biphasic. Interactions between whey proteins and soluble/insoluble whey protein microparticles were thought to be at the origin of the shift. Results also showed that the presence of 20−40% WPI tryptic hydrolysate into the WPI solutions improved whey protein thermal aggregation at pH 6.0. Such a result could not be ascribed only to 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.