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Article Title

Cultivation temperature and length affect the antioxidant activity and total phenolic content of soybean Koji prepared with Aspergillus awamori

Abstract

In this study, soybean koji was first fermented with Aspergillus awamori, a starter organism commonly used for the fermentation of sake, at 25, 30 or 35°C for a period of 1-5 days. Antioxidant activity, including DPPH radical-scavenging effect and Fe2+-chelating ability, and total phenolic content of the methanol extract of these fermented soybean koji as well as mycelial propagation of starter organism were compared. Results revealed that fermented for a same period of 3 days, the DPPH radical-scavenging effect exerted by the 30°C-koji extract was the highest showing 2.5-3.5 folds of that fermented at 25 or 35°C. The Fe2+-chelating ability exerted by the 30°C-koji extract was also found to be 3.6-3.8 times higher than those fermented at other temperatures. Furthermore, it was also noted that increasing or decreasing cultivation time from 3 days resulted in a decreased antioxidant activity of the koji extract. Cultivation temperature and length were also observed to affect the mycelial propagation and the total phenolic content of the koji extract. Maximum mycelial propagation of A. awamori was achieved after cultivation at 30°C for 3 days. Finally, the highest phenolic content noted in 30°C-koji extract was closely correlated to the highest antioxidant activity observed.

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