Effect of solid-state fermentation by three different Bacillus species on composition and protein structure of soybean meal.

BACKGROUND Fermentation efficiency of thermophiles of Bacillus licheniformis YYC4 and Geobacillus stearothermophilus A75, and mesophilic Bacillus subtilis 10 160 on soybean meal (SBM) was evaluated by examining the nutritional and protein structural changes. RESULTS SBM fermenting by B. licheniformis YYC4, B. subtilis 10 160 and G. stearothemophilus A75 increased significantly the crude and soluble protein from 442.4 to 524.8, 516.1 and 499.9 g kg-1 , and from 53.9 to 203.3, 291.3 and 74.6 g kg-1 , and decreased trypsin inhibitor from 8.19 to 3.19, 2.14 and 5.10 mg g-1 , respectively. B. licheniformis YYC4 and B. subtilis 10 160 significantly increased phenols and pyrazines contents. Furthermore, B. licheniformis YYC4 fermentation could produce abundant alcohols, ketones, esters and acids. Surface hydrophobicity, sulfhydryl groups and disulfide bond contents of SBM protein were increased significantly from 98.27 to 166.13, 173.27, and 150.71, from 3.26 to 4.88, 5.03 and 4.21 μmol g-1 , and from 20.77 to 27.95, 29.53 and 25.5 μmol g-1 after their fermentation. Fermentation induced red shifts of the maximum absorption wavelength (λmax) of fluorescence spectra from 353 to 362, 376 and 361 nm, while significantly reduced the fluorescence intensity of protein, especially when B. subtilis 10 160 was used. Moreover, fermentation markedly changed secondary structure composition of SBM protein. SDS-PAGE and AFM analyses showed that macro-molecule protein got degraded into small sized protein or peptide during fermentation of SBM . CONCLUSION B. licheniformis YYC4 fermentation (without sterilization) improved nutrition and protein structure of SBM as B. subtilis 10 160, suggesting its potential application in SBM fermentation industry. This article is protected by copyright. All rights reserved.