Modification of Soybean 11S Protein by Fermentation: Antioxidant Capacity, Oxidative Stability in Emulsions and Structural Evolution

Fermentation is an effective method to enhance the bioactivity of plant proteins, yet the link between the functionality and conformational state of fermented soybean 11S protein (F11S) requires clarification. This study first evaluated the antioxidative efficacy of F11S and its application in emulsion systems, followed by a mechanistic investigation into its structural evolution. Results showed that the bioactivity of F11S was strictly fermentation-time-dependent, reaching its peak at 16 h. At this stage, F11S exhibited maximal scavenging capacities for ·OH (84.51 ± 2.53%) and DPPH radicals (93.84 ± 2.62%). Crucially, in a Tween 20 emulsion system, the F11S-16h fraction demonstrated superior oxidative stability, maintaining the lowest peroxide value (4.33 ± 0.53 mmol/kg) after 15 days of storage. To elucidate the mechanism behind this enhanced functionality, structural analysis was conducted. It revealed that while surface hydrophobicity peaked at 12 h due to protein unfolding, extended fermentation to 16 h induced a refolding process, guiding the protein into a thermodynamically stable conformation. These findings indicate that the stable refolded structure formed at 16 h, rather than maximal hydrophobicity, is the key determinant for the superior antioxidant performance and emulsion stabilizing ability of F11S.