Effect of Different Pretreatment Methods on the Bioconversion of Rice Bran into Ethanol

Abstract

The efficiency of acid, enzyme and microbial pretreatment of rice bran was compared based on the content of cellulose, hemicellulose, reducing sugars and xylose in the substrate. An isolate of Aspergillus niger or a strain of Trichoderma viride (MTCC 800) was employed for microbial pretreatment of rice bran in solid state. Acid pretreatment resulted in the highest amount of reducing sugars followed by enzyme and microbial pretreatment. A. niger showed a higher rate of hydrolysis than T. viride. The rice bran hydrolysate obtained from the different methods was subsequently fermented to ethanol either by Zymomonas mobilis (NCIM 806) or by Pichia stipitis (NCIM 3497). P stipitis fermentation resulted in higher ethanol (37% higher) and biomass production (76~83% higher) than those of Z. mobilis. Maximum ethanol production resulted at 12 h in Zymomonas fermentation, while in Pichia fermentation, it was observed at 60 h. Microbial pretreatment of rice bran by A. niger followed by fermentation employing P. stipitis was more efficient but slower than the other microbial pretreatment and fermentation.