Feasibility of bioethanol production from rice bran

Abstract

Rice bran is a by-product of rice production with a high carbohydrate and starch content and the potential for bioethanol production by alcoholic fermentation. This article describes bioethanol production by Saccharomyces cerevisiae from hydrolyzed defatted rice bran (DRB) a rice by-product applying ultrasonic treatment and protease addition, as well as a sequential strategy of experimental design (SEED). In the first Central Composite Rotatable Design (CCRD), the temperature (25-30 °C) and inoculum concentration (0.5-50 g L-1) had positive effects on bioethanol production, while the effect of pH (4.0-6.0) was not significant. In the second CCRD, the temperature (28-35 °C) and inoculum concentration (10-70 g L-1) had negative and positive effects on bioethanol production (p < 0.05). Protease addition (15 µL g-1) increased the conversion of substrate into bioethanol by 76%. The optimized conditions for the production of 40.7 g L-1 bioethanol were a temperature of 31.5 °C and an inoculum concentration of 70 g L-1. Validation in a benchtop bioreactor produced 40.0 g L-1 of bioethanol from hydrolyzed DRB, and the SEED was characterized as a useful tool to improve bioethanol production from DRB. Furthermore, the DRB proved to be a by-product with great potential for bioethanol production, derived from alternative sources not commonly used in human food.