Bioethanol production from Brewer’s rice by Saccharomyces cerevisiae and Zymomonas mobilis: evaluation of process kinetics and performance

Abstract

ABSTRACT Brewer’s rice, or known as temukut in Malaysia, is a by-product of rice processing typically sold cheaply as animal feed because of its low esthetic value and lack of suitability for human consumption. To date, few works have discussed its utilization in bioethanol production for fuel or industrial usage. Due to its low price, availability, and high carbohydrate content, brewer’s rice possesses high potential to be an alternative raw material for bioethanol production. This work was aimed at evaluating the viability of ethanol production from brewer’s rice by comparing the kinetics and performance of bioethanol production using Saccharomyces cerevisiae and Zymomonas mobilis respectively. Prior to batch fermentation with S. cerevisiae and Z. mobilis, the brewer’s rice was first gelatinized with diluted HCl and then hydrolyzed using amylolytic digestion to produce a sugar-rich hydrolyzate. Overall, superior ethanol productivity was obtained with the bacterium compared to the more commonly used yeast (70.71% yield vs 31.35% yield). Using the modified Gompertz model, maximum potential bioethanol concentration (Pm ) of 9.85 g/L, maximum bioethanol production rate (rpm ) of 0.89 g/L/h and lag time (tL ) of 1.88 h were observed for Z. mobilis, demonstrating superior fermentative capability compared to the yeast. The findings demonstrated the viability of brewer’s rice as a raw material for efficient ethanol production using Z. mobilis as an appropriate fermenting microorganism. Results also point to the sustainable use of waste in rice processing and diversification of end uses of brewer’s rice, among others.