Disulfide Bond Formation Affects Stability of Whey Protein Isolate Emulsions

The viscosity and degree of flocculation of 20 wt% n‐hexadecane oil‐in‐water emulsions stabilized by whey protein isolate (1 wt% WPI in 0.05M phosphate buffer, pH 7.0) increased as the emulsions aged. These effects were reduced when N‐ethylmaleimide, a sulfhydryl blocking agent, was added to the emulsions immediately after homogenization, but were not completely eliminated. Gel electrophoresis (SDS‐PAGE) showed an increase in the extent of intermolecular disulfide bond formation between proteins absorbed at the droplet interface with time. Floes were probably formed initially by noncovalent bonding or bridging flocculation, and then stabilized by disulfide bonds between proteins absorbed to different droplets.