Effects of Germination on the Structure and Digestive Characteristics of Soybean Protein in the Simulated Gastrointestinal Environment of the Elderly

This study mainly explored the changes in protein structure during the germination process of soybeans and analyzed the influence of protein structure changes on protein digestion characteristics through an elderly gastrointestinal digestion model. The results showed that average particle size and disulfide bond content were lowest (64.6 μm and 13.13 μmol/g, respectively) at 72 h after germination, meanwhile, the β-sheet content was lower (12.10%), while the β-turn and random curl contents were higher than those at 0 h without germination (14.13% and 21.26%, respectively), they were 14.18% and 21.84%, respectively. The α´ subunit, α subunit of 7S and A subunit of 11S gradually disappeared with time after germination and λ_max showed a redshift, exposing more hydrophobic amino acids. Pearson correlation analysis showed that protein digestibility was negatively correlated with disulfide bond, β-sheet, and average particle size of digestible products (P<0.001) and positively correlated with the surface hydrophobic index of digestible products. The surface hydrophobic index of digestive products and proteolysis degree of digestive end products were negatively correlated with disulfide bond and β-sheet, but positively correlated with α-helix and random curling content. Therefore, it was inferred that the protein digestibility of the germinated group at 72 h was 1.53% higher than that of the non-germinated group, which was caused by the changes in digestive characteristics caused by the changes in protein structure during treatment. In conclusion, germinated soybean protein powder is more conducive to digestion and absorption in the elderly, and the protein powder prepared from germinated soybean can be used as an ideal source of protein.