Structural, physiochemical, and tribological properties of whey protein-based microgels: Effects of pH and ion strength

Microgels were formed from whey protein isolate (WPI) and two hydrocolloids, gelatin A (Gel A) and sodium alginate (SA), at different pH and ion strengths. Surface Plasmon Resonance (SPR) results showed that both hydrocolloids interact with WPI. Decreasing pH or increase ion concentration from natural conditions encouraged the complexation of biopolymers. In acid-induced system, microstructure results showed that WPI-SA exhibited well core/shell structure, with homogeneous aggregation, especially at pH 5.4, while WPI-Gel A showed more severe phase separation. In ion-induced system, both WPI-Gel A and WPI-SA showed decrease in the absolute zeta potential values and increase in viscosity, especially in WPI-SA. WPI-SA showed much better lubricity than WPI-Gel A in both systems. However, WPI-SA at natural conditions still showed the better overall lubricity than other samples, indicating the importance of particle size. In addition, sodium alginate significantly enhanced the storage stability of WPI particles after acid treatment and heat treatment. Hence, the properties of the complexed particle of WPI and other hydrocolloids could be tuned by adjusting the pH or ion concentration. The complexation of sodium alginate with WPI particles presents a promising strategy for enhancing the lubricating properties of proteins and developing more nutritious fat substitutes.