Hydroxyl Radical-Stressed Whey Protein Isolate: Functional and Rheological Properties

The objective of the study was to examine the sensitivity of whey protein functionality to oxidizing radicals. Whey protein isolate (WPI) was oxidatively stressed by incubation at 20 °C for 3, 5, and 10 h in hydroxyl radical-generating media containing 0.1 mM ascorbic acid, 0.1 mM FeCl3, and 1–10 mM H2O2. Protein solubility decreased (P < 0.05) with increasing H2O2 concentrations and oxidation time. Surface properties of WPI, including both emulsifying and foaming activities, exhibited significant improvements (P < 0.05) at H2O2 concentrations up to 5 mM and oxidation time up to 5 h. The longer oxidation time or higher H2O2 concentrations tended to diminish the surface functionality. However, the oxidative stress, though decreasing the onset gelling temperature, had a general detrimental effect on WPI gelation (hardness, springiness, and storage modulus). The results indicated opposing effects of oxidation on WPI: detrimental to hydrodynamic properties (solubility, gelation) but beneficial to surface properties (emulsification, foaming).