Enhancement of bioactivity of rice bran by solid-state fermentation with Aspergillus strains

Rice bran was subjected to solid-state fermentation for 8 and 14 days using different Aspergillus strains: A. brasiliensis, A. awamori, and A. sojae. Alcoholic extracts (95% ethanol) from the fermented rice bran were analyzed for DPPH• scavenging activity and cosmeceutical activity (tyrosinase and elastase inhibitory activities). The levels of bioactive components including total phenolics, total flavonoids, kojic acid, and phenolic acids were also determined. The fungal fermentation increased the cosmeceutical activities and overall content of the bioactive components. Aspergillus sojae sample exhibited the highest radical scavenging activity and tyrosinase inhibitory activity (IC₅₀ 1.55 mg/mL) after 6 days of fermentation, whereas A. brasiliensis sample showed the highest elastase inhibitory activity. Kojic acid appeared to be one of the key substances responsible for the tyrosinase inhibition activity of the alcoholic extracts. Extensive fermentation over a week, however, induced the loss of phenolic acids and cosmeceutical activity, indicating that proper control of the fermentation period was critical.