Two-step fermentation of cooked rice with Aspergillus oryzae and Clostridium acetobutylicum YM1 for biobutanol production

In Asia, uneaten cooked rice is the highest portion amongst many forms of food wastes that are thrown away. In order to make use of the thrown-away rice and potentially use it for liquid fuels, steamed Japanese rice was evaluated on biobutanol production through a two-step fermentation by amylase-producingAspergillus oryzae, and solvent-producingClostridium acetobutylicumYM1. The effects of sterilization and providing anaerobic conditions on solvent production in acetone-butanol-ethanol (ABE) fermentation cannot be underestimated. Several conditions, including aerobic, anaerobic, sterile, and non-sterile were investigated concerning the solvent production capability ofClostridium acetobutylicumYM1. The maximum solvent production was 11.02 +/- 0.22 g/l butanol and 18.03 +/- 0.34 g/l total ABE from 75 g/l dried rice. The results confirmed that the solvent production performance of the YM1 strain was not affected by the sterilization conditions. In particular, 10.91 +/- 0.16 g/l butanol and 16.68 +/- 0.22 g/l ABE were produced under non-sterile and aerobic conditions, which can reduce industrial-scale production costs.