Regular articleBioconversion of soybean residue for use as alternative nutrient source for ethanol fermentation

- Soybean residue (SR) and waste cooked rice (CR) were used for ethanol production.
- Supplementing SR with CR enhanced protease production in solid-state fermentation.
- SR hydrolysate provided adequate free amino nitrogen for ethanol fermentation.
- Ethanol production of 40.7 g L−1 with a yield of 0.42 g g−1 was obtained.
- Bioconversion processes and mass balances of SR to ethanol are proposed.

Soybean residue (SR) was transformed, through solid-state fermentation by Aspergillus oryzae TISTR 3087 followed by hydrolysis, to a solution rich in free amino nitrogen (FAN), and used as the nitrogen source in an ethanol fermentation. Supplementing SR with waste cooked rice (CR) at a 75:25 mass ratio increased dramatically the production of protease compared to a fermentation with SR as the sole substrate (2822 U g−1 substrate against 33 U g−1). Subsequent hydrolysis of the solid-state fermented solids produced as much as 1.8 g-FAN L−1. The SR-derived hydrolysate was mixed with sugarcane molasses, to an initial sugar concentration of 110 g L−1, and used for ethanol production by Saccharomyces cerevisiae TISTR 5339. The yeast produced 40.7 g ethanol L−1 with a yield of 0.42 g g‐sugar−1 and a productivity of 0.62 g L−1 h−1. This study demonstrates clearly that co‐fermentation of SR and CR enhances protease production, and that SR is a feasible and low cost source of nitrogen for ethanol fermentation.