Structure Changes in Relation to Digestibility and IgE-Binding of Glycinin Induced by pH-Shifting Combined with Microbial Transglutaminase-Mediated Modification

This study aimed to evaluate the effects of pH-shifting treatment combined with microbial transglutaminase (MTG)-mediated modification on the structure, digestibility, and IgE-binding of glycinin. Glycinin was incubated in acidic (pH 1.0) or alkaline (pH 13.0) solutions to induce protein structure to unfolding followed by refolding for 1 h at pH 7.0. Afterwards, glycinin was incubated with MTG under appropriate conditions. Sodium dodecyl sulfate polyacrylamide gel electropheresis(SDS-PAGE), circular dichroism, UV absorption spectra, and surface hydrophobicity were considered to measure the changes in the structure of glycinin. The digestibility and IgE-binding of glycinin were determined by Tricine-SDS-PAGE and ELISA, respectively. The results showed that pH 1.0 shifting caused the unfolding of the spatial structure of glycinin and the formation of some polymers via disulfide bond. After glycinin was incubated with MTG, the protein preferentially underwent embedding and folding. The acidic compound-modified glycinin was stable for digestion. Under pH 13.0 shifting treatment, glycinin was partially hydrolyzed, and the MTG-modified alkaline-treated glycinin was slightly affected with a good digestibility. Compound modification could reduce the IgE-binding of glycinin, especially under alkaline conditions. Our findings suggested that alkaline pH shifting combined with MTG cross-linking can be an efficient approach to reduce the IgE-binding of glycinin with a labile digestion.