Protein-polyphenol conjugation through alkali treatment improves the structure and functionality of gluten

The conjugates of gluten and polyphenols (naringin, hesperetin or curcumin) were produced by alkaline method and the effects of conjugation on physicochemical properties of gluten were investigated in this study. The results show that the conjugates possess lower content of free amino and sulfhydryl groups, and higher molecular mass, which indicate the covalent binding occurred. As compared with corresponding mixtures, the conjugates show lower intensity of the amide A, surface hydrophobicity, intermolecular beta-sheets, interfacial and surface tension, as well as higher fluorescence intensity, antiparallel beta-sheets and particle size (in the range of 130-150 mu m). Furthermore, the conjugates also exhibit better emulsifying and foaming properties, higher storage modulus and lower degradation temperature than native gluten. However, the changes in physicochemical properties of conjugates depend on the type of polyphenols and curcumin-gluten conjugates possess the improved emulsifying, foaming and gelation properties among conjugates, due to their more flexible structure.