Low temperature extrusion promotes transglutaminase cross-linking of whey protein isolate and enhances its emulsifying properties and water holding capacity

Impact of extrusion pretreatment (50, 70, 90, 110 and 130 °C) on physicochemical, emulsifying properties and water holding capacity (WHC) of transglutaminase (TGase) cross-linked whey protein isolate (WPI) were investigated in this study. The results of molecular size distribution and SDS-PAGE proved that there were more macromolecular polymers formed in TGase cross-linked WPI after extrusion pretreatment (E-WPI-TGase) and the consumption of free amino groups for E-WPI-TGase was the largest at the extrusion temperature of 50 °C and 70 °C. As the extrusion temperature increased from 90 °C to 130 °C, particle size of WPI after extrusion pretreatment (E-WPI) was not changed significantly, compared with that of E-WPI-TGase (p > 0.05). In addition, the emulsifying properties, surface hydrophobicity and WHC of E-WPI-TGase were higher than those of WPI cross-linked by TGase (WPI-TGase) (p