Total phenolic and anthocyanin contents, as well as antioxidant activity, of black bean koji fermented by Aspergillus awamori under different culture conditions

Solid state fermentation was performed by growing Aspergillus awamori, a food grade fungus, on steamed black bean at 25, 30 or 35 °C for 3 days or at 30 °C for 0–5 days to prepare black bean kojis. It was found that fermentation for a period of 3 days at 30 °C yielded a koji that contained the highest amount of total phenolics and anthocyanins among the various kojis examined. Using this 3-day cultivation period, the 30 and 35 °C-koji exhibited the highest Fe2+-chelating ability and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical-scavenging effect, respectively. Results obtained with kojis prepared at 30 °C for 0–5 days revealed that total phenolic content increased as the fermentation period was increased and became highest on the 4th day and then declined, while the 3-day koji showed the highest anthocyanin content. Further extending the fermentation period did not change the anthocyanin content of the koji significantly (p > 0.05). Generally, the highest DPPH radical-scavenging effect and Fe2+-chelating ability could be obtained with kojis fermented at 30 °C for 3–4 day. The DPPH radical-scavenging effect and the Fe2+-chelating ability exhibited by these kojis were about 2.64–3.20- and 1.77–2.16-fold greater than those of the unfermented black bean, respectively.