Effect of ultrasound pre-treatment on formation of transglutaminase-catalysed soy protein hydrogel as a riboflavin vehicle for functional foods

High intensity ultrasound (HIU) treated soy protein isolate (SPI) and non-HIU-treated SPI were cross-linked by transglutaminase to form hydrogels. SDS-PAGE showed that HIU increased the amount of high molecular weight aggregates, likely due to the formation of epsilon-(gamma-glutamyl) lysine bonds. Moreover, HIU pretreatment increased the hydrophobic nature of transglutaminase gels as demonstrated by FT-Raman. Hill changed the 3D-network structure of transglutaminase induced SPI gel with riboflavin (TSGR). Furthermore, 40 mm HIU increased gel yield, riboflavin encapsulation efficiency and gel strength of TSGR. HIU decreased swelling and protein erosion of TSGR in simulated gastrointestinal fluids. It also resulted in reduced riboflavin release rate and altered the release mechanism in simulated gastrointestinal fluids both in the absence and presence of digestive enzymes. In conclusion, HIU may facilitate covalent cross-linking, increase hydrophobicity and change the 3D network of TSGR, leading to differences in hydrogel stability, as well as riboflavin encapsulation and release profiles. (C) 2015 Elsevier Ltd. All rights reserved.