DOI: 10.14457/tu.the.2016.592
title: Effect of protein modification methods on physicochemical and functional properties of proteins

description: The aim of this study was to investigate the influence of the protein modification methods including high intensity ultrasound (HIU) treatment, succinylation, hydrogen peroxide (H2O2) treatment, glycosylation using glucose and maltose and enzymatic cross-linking by transglutaminase enzyme on the physicochemical and the functional properties of mung bean protein isolates (MPI), whey protein isolates (WPI) and pasteurized liquid egg white (PLEW). The physicochemical properties of proteins including Z-average,      -potential, surface hydrophobicity (H0), free sulfhydryl (SH) group content, and molecurlar weight (MW) and the functional properties of proteins including solubility, foaming properties (foam capacity or FC and foam stability or FS), emulsifying properties (emulsifying activity index or EAI and emulsifying stability index or ESI), gel hardness and rheological properties were investigated. The influence of HIU treatment at 0-3400 joules on the physicochemical and the functional properties of proteins was studied. The result showed that HIU treatment decreased the Z-average of all proteins and also increased the Zeta potential and the H0 of WPI. Moreover, HIU treatment decrease the foaming properties of PLEW and also decrease the ESI of MPI but increase the gel hardness of MPI and WPI. The influence of succinylation at 0-0.10 succinic anhydride:protein weight ratio on the physicochemical and the functional properties of proteins was studied. The degree of N-acylation of all proteins increased with the increasing of succinic anhydride:protein weight ratios. Succinylation had no impact on (i) the total free SH groups of all proteins, (ii) the exposed free SH groups of MPI, (iii) the FC of MPI and PLEW, (iv) the ESI of MPI and PLEW and (v) the final G' of MPI. Succinylation increased (i) the MW and the EAI of all proteins, (ii) the Z-average of MPI and WPI, (iii) the exposed free SH groups of WPI and PLEW, (iv) the ESI of PLEW, and (v) the final G' of WPI. Succinylation shifted the lowest solubility point (pI) of all proteins to more acidic pH. Succinylation decreased (i) the Zeta potentials, (ii) the H0, (iii) the FS, (iv) the gel hardness of all proteins, (v) the Z-average of PLEW, (vi) the FC of WPI, and (vii) the gelation temperature of MPI. However, succinylation increased the gelation temperature of WPI and PLEW. The influence of H2O2 treatment at concentration of 0-20 mM on the physicochemical and the functional properties of proteins was studied. H2O2 treatment did not affect on the exposed free SH groups of MPI and WPI but decreased the exposed free SH groups of PLEW. H2O2 treatment also increased the FS of MPI and WPI but had no impact on the FS of PLEW. In addition, the gel hardness of all proteins was altered depending on the protein types and H2O2 concentrations. The influence of the glycosylation with 0-20 wt% glucose and maltose at 30-70 ºC for 1 h on the physicochemical and the functional properties of proteins was studied. The result showed that glycosylation had impact on the physicochemical and the functional properties of proteins. However, the physicochemical and the functional properties of proteins were altered depending on the reaction temperature, sugar concentration, and protein type. The influence of the transglutaminase enzymatic treatment at enzyme:protein weight ratio of 0:1-0:400 on the physicochemical and the functional properties of proteins was studied. The enzymatic treatment had no impact on (i) the Zeta potential, the exposed free SH group content, the protein solubility, the foaming and the emulsifying properties of all proteins,  (ii) the Z-average of WPI, and (iii) the MW of WPI and PLEW. In contrast, the Z-average of MPI and PLEW increased after treated with enzyme. In addition, enzymatic treatment increased (i) the MW of MPI, and (ii) the gel hardness of all proteins. Therefore, these modification methods could be used to improve the physicochemical and functional properties of MPI, WPI and PLEW. Moreover, these modification methods would be able to apply to the other protein applications.