MECHANISM OF UREA-INDUCED WHEY-PROTEIN GELATION

Whey protein isolate (WPI) at an 11.0% concentration spontaneously formed a gel at 25 °C in 6 M urea. As the pH was increased from 7 to 10, gel formation, from a viscous sol to an elastic network, was accelerated. Addition of N-ethylmaleimide up to 6 mM inhibited gelation. The sulfhydryl (SH) content of WPI decreased during urea incubation, especially with increasing pH. Electrophoretic analyses revealed the progressive disappearance of α-lactalbumin, β-lactoglobulin, and serum albumin during the gelation process with concomitant formation of polymers of these proteins. The spontaneous formation of gels in 6 M urea resulted from protein-protein cross-linkages via oxidation of thiol groups and SH-disulfide interchange reactions. © 1990, American Chemical Society. All rights reserved.