Optimization of fermentation conditions to improve the functional and structural characteristics of rapeseed meal with a mutant Bacillus subtilis species

This investigation aimed to provide the optimum solid-state fermentation (SSF) conditions to enhance the functional and structural characteristics of rapeseed meal (RM). Response Surface Methodology (RSM) was used to optimize the experimental fermentation conditions (temperature, incubation time, and inoculum size) on the protease activity, peptide content, and DPPH activity of RM with Central Composite Design (CCD). The quadratic models of the investigated responses were developed, and their coefficients were observed from the multiple-regression analysis. ANOVA indicated that incubation time was highly significant (p < .01) in all experimental responses. The optimized fermentation conditions of protease activity, peptide content, and DPPH activity were accessed at 92 h, 44 °C, and 8 mL, and the predicted data for these responses were 212.59 U/g, 192.35 mg/g, and 93.46%, respectively. The verification experiment indicated that the measured values of the three responses were insignificant (p > 0.05) with the predicted results, suggesting that the CCD model was fittingly used in predicting such responses. Scanning electron microscopy (SEM), atomic force microscopy (AFM), and Raman spectroscopy outcomes showed remarkable alteration in RM morphology, surface topography, and secondary conformation after 92 h of fermentation. Correlational analysis indicated that β-turn had a strong interrelationship with the functional properties (i.e., DPPH, total phenol content, and Emulsifying properties) of FRM. The improved parameters obtained displayed their effectiveness in improving the bioactive and structural properties of FRM.