Fabrication and characterization of acid-induced gels from thermally-aggregated egg white protein formed at alkaline condition

Cold gelation of egg white proteins (EWP) has still remained a challenge because they suffer from heat-induced gelation at low protein concentrations during the preheating step. This study suggested that adjusting pH of EWP solution at relatively high alkaline pH (i.e. 11.3) could inhibit the heat-induced gelation of EWP, allowing to produce thermally aggregated EWP (TA-EWP) at relatively high protein concentrations during the preheating step. Regarding SDS-PAGE, free-SH groups, circular dichroism, and surface hydrophobicity data, the preheating step at alkaline pH probably caused the TA-EWP are assembled from the partially unfolded protein molecules which stabilized by numerous disulfide bonds as well as hydrophobic interactions that develop a network of the beta-sheet structures. The TA-EWPs are able to form acid-induced cold-set gels. SEM images showed the TA-EWP acid-induced gels had a honeycomb-like microstructure contained large serum pools. With increasing preheating temperature and protein content, the microstructure of the gels became more compact and all texture parameters including hardness, springiness, chewiness, cohesiveness as well as Young's modulus, true fracture stress (sigma) and Hencky strain tend to increase. Furthermore, the water holding capacity (WHC) improved with increasing protein content and preheating temperature. All TA-EWP acid-induced gels exhibited a weak dependence of storage modulus (G') with frequency and the G' value of the acid-induced gels increased with increasing preheating temperature and protein content.