Enzyme-induced gelation of whey proteins: Effect of protein denaturation

Abstract

The enzyme-induced gelation properties of unheated and denatured whey proteins (WP) were investigated. Solutions (9%, w v ) of whey protein isolate (WPI) were denatured by heating at 80 °C for 2–30 min, and gelation was induced by incubation with a Bacillus licheniformis protease (40 °C, pH 7.0). The gelation characteristics, as well as 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 unheated and pre-heated WP, but the gelation process was strongly dependent on the extent of denaturation (%D). Higher %D resulted in earlier gelation and a faster increase in gel firmness. The relation between %D and the rate of gel firming was almost linear. The strength of the enzyme-induced gels increased continuously during 30 h of incubation. After 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 (≈8%D). The latter gel had a particulate microstructure, whereas the gel from the highly denatured WPI (98%D) had a fine-stranded structure. This enzyme-induced gelation of partly denatured WP may be of interest for food applications.