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 0.05 M phosphate buffer, pH 7.0) increased as the emulsions aged. These eff ects 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 in crease in the extent of intermolecular disulfide bond formation betwee n proteins absorbed at the droplet interface with time. Flocs were pro bably formed initially by noncovalent bonding or bridging flocculation , and then stabilized by disulfide bonds between proteins absorbed to different droplets.