Effects of Storage Time and Hydrogen Peroxide on the Formation of Soy Globulin 15S in 11S Dilute Solutions Investigated by Analytical Ultracentrifugation

Two soy protein 11S fractions with different surface sulfhydryl contents were prepared. Utilizing analytical ultracentrifugation, the effects of storage time and hydrogen peroxide at different concentrations (0.5–100 mmol/L) on the two 11S fractions were investigated. Results show that after removing 2-mercaptoethanol (2-ME) by size exclusion chromatography, the 11S fraction with high surface sulfhydryl content (2.0 mol sulfhydryl/mol 11S) progressively formed 15S and 21S in dilute solutions during storage at 4 °C for 82 days. While, the 11S fraction with low surface sulfhydryl content (0.2 mol sulfhydryl/mol 11S) was stable under the same condition. Moreover, after treating the 11S with high surface sulfhydryl content with 1 mmol/L H₂O₂, the weight percentage of 15S reached the maximum value of 20%. The 15S induced by air and H₂O₂ could be totally converted to 11S with the addition of 10 mmol/L 2-ME, which could be attributed to that the disulfide bond linking two 11S molecules is on the surface of the 15S and easily accessible to the reducing agent 2-ME. This study helps us to deeply understand the formation mechanism of 15S and the stability of 11S.