Formation and characterization of cold-set whey protein gels induced by L-ascorbic acid/calcium for their encapsulation and release

Abstract

Protein cold-set gels are potential carriers for the encapsulation of bioactive compounds. Meanwhile, bioactive compounds have also been used as cross-linkers or accessories for protein gelation, but their encapsulation has not been investigated during gelation for potential nutritional value. In this study, cold-set gels of whey protein isolate (WPI) were induced by L-ascorbic acid (L-AA) at pH 4.0–6.0, L-ascorbic acid plus CaCl2 at pH 3.8, or L-ascorbic calcium at pH 7.0. The range of pH for WPI gelation induced by L-AA narrowed with the decrease of WPI content from 10% to 6% (w/v). The gel networks were stabilized by non-covalent and covalent interactions, which difference was dependent on the use of cross-linkers. L-Ascorbic recoveries were above 76% in WPI hydrogels, where the highest recovery reached 98%. L-Ascorbic encapsulation efficiency ranged from 69% to 100%. Hydrogels and cyrogels varied from a smooth and dense structure to a coarse structure. L-ACa at 16 mM induced uniform and compact structure of both gels and the highest hardness and storage modulus of hydrogel. L-Ascorbic groups were effectively immobilized into WPI gels via their interaction with whey protein and calcium. L-Ascorbic loading capacity in WPI hydrogels and gel powder increased as the pH decreased and its calcium concentration increased. The release of free L-ascorbic acid from gel powder was independent on protein re-hydration. These results suggest the potential use of protein cold-set gels for the encapsulation and delivery of bioactive compounds with themselves or their combination with calcium as cross-linkers.