Changes of Physico-Chemical Properties of Whey Protein after Denaturation, Enzymatic Hydrolysis and Cross-Linking

In the current research, physico-chemical properties of whey protein isolate (WPI) and its resulting compounds including denatured whey protein isolate (DWPI), cross-linked whey protein isolate (CWPI), whey protein hydrolysate (WPH) and cross-linked whey protein hydrolysate (CWPH) were analyzed. Enzymatic hydrolysis and cross-linking were performed by pepsin (at 37°C for 30 min) and transglutaminase (at 50°C for 20 h), respectively. The obtained results stated that, by moderate heat, DWPI had smaller average size (44 nm) and more zeta-potential rather than native WPI. Intensity of the number of molecules with higher average particle size has been reduced by cross-linking of both DWPI and WPH using transglutaminase. Also, the antioxidant activity of WPH was increased from 0.398 to 0.519 through cross-linking and making larger peptide chain. The result of fourier-transform infrared spectroscopy (FTIR) indicated the enzymatic cross-linking owing to the formation of new C−N bonds between the α-carbon of lysine and the primary amine group of glutamine displaced the corresponding band at both CWPI and CWPH samples.