Effect of single and two-stage fermentation on the antioxidative activity of soybean meal, and the structural and interfacial characteristics of its protein

The efficiency of single and two-stage solid-state fermentation (SSF) of soybean meal (SBM) by thermophilc Bacillus licheniformis YYC4 was examined. Crude and soluble protein contents were significantly increased after SSF, especially two-stage SSF (TS-SSF), however, substantial reduction in trypsin inhibitor was observed. Additionally, TS-SSF significantly enhanced the reducing power and scavenging DPPH, hydroxyl and ABTS radical activities of SBM. On the other hand, TS-SSF significantly reduced the α-helix, fluorescence intensity and caused a red-shifted in the maximum absorption wavelength (λmax), but increased the surface hydrophobicity, β-sheet, and sulfhydryl group and disulfide bond content of SBM protein (SBMP). Again, SSF, particularly TS-SSF, reduced the particle size of SBMP, leading to a corresponding decrease in apparent viscosity. Compared to the single-stage SSF (SS-SSF), TS-SSF caused significant improvement in the interfacial properties of SBMP. Likewise, SBM fermented by TS-SSF had higher nutritional value, better antioxidative activity and interfacial properties than the SS-SSF sample.