Rheological and Structural Characterization of Whey Protein Gelation Induced by Enzymatic Hydrolysis

Abstract

Whey proteins hydrolyzed by Bacillus licheniformis protease (BLP) form soft and turbid aggregate gels with potential food and biotechnological applications. The purpose of the study was to characterize protease-induced whey protein gelation by comparing different protein and enzyme concentrations in terms of gel mechanical and microstructural properties, and conformational changes in the protein secondary structure due to hydrolysis and gelation. Gels formed with whey protein isolate (WPI), at concentrations 5 and 10% (w/v), and BLP concentrations, BLP/WPI (w/w), of 1, 3, and 5% were studied. Regardless of the enzyme concentration, gels with 10% WPI were strong and elastic while those with 5% WPI were weak. Gelation time decreased as the enzyme concentration increased for both protein concentrations. Gel strengths values of 10% WPI samples were independent of BLP concentrations at the end of the incubation period. Creep tests performed on the resulting gels showed that 10% WPI gels with different BLP concentration had similar elasticity, slightly increasing with BLP amount. Remarkable differences were observed in the microstructures of gel prepared with different concentrations of protein and BLP. Changes in the protein secondary structure measured during the gelation were small before gelation. However, sudden changes were observed when the samples gelled, and also after 7 h of incubation at 50 degrees C (time in which samples reached a plateau in G* as seen by rheology tests). Results revealed that without enzyme, hydrolysis of the protein was not promoted and the protein secondary structure remains the same; only a slight denaturation was observed when the protein was incubated at 50 degrees C. (C) 2016 Elsevier Ltd. All rights reserved.