ENZYME-INDUCED GELATION OF WHEY PROTEINS - EFFECT OF PROTEIN DENATURATION

The enzyme-induced gelation properties of unheated and denatured whey proteins (WP) were investigated. Solutions (9%, w/v) of whey protein i solate (WPI) were denatured by heating at 80 degrees C for 2-30 min, a nd gelation was induced by incubation with a Bacillus licheniformis pr otease (40 degrees C, pH 7.0). The gelation characteristics, as well a s gel strength and microstructure, were examined. The heat treatments resulted in irreversible denaturation of up to 98% of the WP. Bacillus licheniformis protease (BLP) was able to induce gelation of both unhe ated and pre-heated WP, but the gelation process was strongly dependen t on the extent of denaturation (%D). Higher %D resulted in earlier ge lation and a faster increase in gel firmness. The relation between %D and the rate of gel firming was almost linear. The strength of the enz yme-induced gels increased continuously during 30 h of incubation. Aft er 9 h, the gel with 98%D was 3.2 times stronger than that with 47%D, and 18 times stronger than the gel from unheated WPI (approximate to 8 %D). The latter gel had a particulate microstructure, whereas the gel from the highly denatured WPI (98%D) had a fine-stranded structure. Th is enzyme-induced gelation of partly denatured WP may be of interest f or food applications. (C) 1997 Elsevier Science Limited.