Structural change and functional improvement of wheat germ protein promoted by extrusion

This study aim to evaluate the effects of extrusion treatment (130–150︒C, 40–48 Hz) on the physicochemical and functional properties of defatted wheat germ protein (DWGP). The results indicated that extrusion could cross-link proteins and starch in defatted wheat germ to produce protein-polysaccharide conjugates and effectively reduce free sulfhydryl groups and surface hydrophobicity of DWGP. The SDS-PAGE showed that DWGP molecular weight decreased after extrusion, but there was no significant difference between different extrusion conditions. The folding and spatial structural changes of DWGP conjugates molecules after extrusion were observed by fluorescence spectroscopy and FTIR. Transformation of α-helix to β-sheet caused high solubility and emulsification. The solubility, emulsification, and in vitro digestibility of DWGP conjugates were increased by 65.90%, 50.52% and 528%, respectively, after the extrusion of 140︒C and 44 Hz. As the extrusion temperature increased, the related functionality decreased. Also, many small and dense lumps in treated DWGP conjugates were observed by SEM. Therefore, extrusion possesses excellent potential as a processing technology to improve the functionality of DWGP.