MECHANICAL-PROPERTIES AND WATER-VAPOR PERMEABILITY OF EDIBLE FILMS FROM WHEY-PROTEIN ISOLATE AND N-ETHYLMALEIMIDE OR CYSTEINE

The role of sulfhydryl/disulfide interchange in determining the water vapor permeability (WVP) and mechanical properties of edible films fro m whey protein isolate (WPI) was investigated. Nearly total inhibition of sulfhydryl/disulfide interchange by the sulfhydryl blocking agent N-ethylmaleimide (NEM) reduced protein solubility by 50%, but had no e ffect on WVP, Young's modulus, yield stress, or breaking stress. Break ing strain was reduced significantly at high levels of added NEM. Redu ction of disulfide bonds with cysteine had no effect on WVP. The effec ts of hydrogen bonding far outweigh those of disulfide bonding in WPI films.