Improving the solubility of wheat gluten: Establishing and characterizing wheat gluten-phosvitin complex at molecular and subunit levels

Wheat gluten (WG) has excellent processing properties, however, its utilization in food industry has been largely restricted for the low solubility. We are interested in improving its solubility with simple and effective approach to broaden its application. Phosvitin (PSV) is a kind of yolk proteins with high solubility. In this work, a co-soluble system (WG-PSV complex) has been established under pH-shifting treatment. After that, the solubility of WG is effectively increased from 16.2% to 43.1%. The WG-PSV complex has smaller particles, a higher Zeta-potential, and a more flexible secondary structure compared to native WG. Meanwhile, the free sulfhydryl group content in WG-PSV complex was 12.24 μmol/g, which was higher than that of native WG (9.05 μmol/g), and its free amino group was much lower than that of native WG. In addition, the proteomics was used to compare the subunit composition in WG-PSV complex and native WG to identify key subunits related to improvement of solubility. It shows that compared to native WG, the subunits A0A3B5ZSZ8 and A0A1D5UUP9 derived from WG have been significantly upregulated, and Q306F8, A0A0E3UQV1 and Q8H738 have been significantly downregulated. In conclusion, pH-shifting is a successful method to establish WG-PSV complex to effectively improve the solubility of WG. And disulfide bonds, amide bonds and hydrophobic contacts were the main interaction forces. Some key subunits were identified to largely determine the forming of protein complex. This study provides a theoretical foundation for enhancing solubility of WG, which would widely expand its applications in food industry.