Abstract
In the present study, kojic acid fermentation by mutated Aspergillus oryzae strain M3B9 was investigated with the aim of improving productivity. When 2.5 g/L yeast extract or 15 g/L rice bran was used as nitrogen source along with 100 g/L sucrose as carbon source, the highest kojic acid production of 42.1 g/L and 41 g/L, respectively, were obtained. In addition, the nature of the nitrogen source had a great influence on the fungal morphology. Yeast extract as nitrogen source can induce pellet formation, which is favorable for repeated batch operation. Similar performances in the fermentor as well as in shake flask with the highest productivity(up to 5.1 g kojic acid/L/day) revealed the practicability of using the mutated strain for large scale kojic acid production. In repeated batch experiments using cell-retention fermentor, the mutated strain maintained high kojic acid production capability throughout the fermentation with three times of medium exchange.