Effect of particle size and ammonium sulfate concentration on rice bran fermentation with the fungus Rhizopus oryzae

The effects of rice bran particle size (0.18–0.39 mm) and ammonium sulfate concentration in the nutrient solution (2–8 g/L) on biomass production, protein and phenolic content generated by solid state fermentation with the fungus Rhizopus oryzae (CCT 1217) were studied. Particle size had a positive effect on biomass production and a negative effect (p ⩽ 0.05) on protein and phenolic contents. Ammonium sulfate concentration had a positive effect (p ⩽ 0.05) on biomass and phenolic content gain. Cultivation of fungus in rice bran with particle size of 0.18 mm and in the presence of 8 g/L ammonium sulfate, resulted in protein levels of 20 g/100 g dry wt and phenolics content of 4 mg/g dry wt. These values were 53 and 65% higher than those achieved with unfermented rice bran. The results demonstrate that the fermentation process increased the value of compounds recovered for potential use in food formulations.