Evaluation of ethanol production from pito mash using <i>Zymomonas mobilis</i> and <i>Saccharomyces cerevisiae</i>

Abstract

This study investigated the potential of pito mash (waste from sorghum brewing) as alternative and cost-effective feedstock for bioethanol production by means of fermentation using Zymomonas mobilis and Saccharomyces cerevisiae isolated from freshly tapped palm wine. Fermentation parameters such as pH, temperature and incubation period were studied. The fermentation microbes, Z. mobilis and S. cerevisiae were identified using API^TM test kit and morphological characteristics, respectively. Analysis of reducing sugar residue was performed using dinitrosalicylic acid (DNS) method, while analysis of ethanol content was performed using gas chromatography. Pito mash recorded total starch content of 6.69%, reducing sugar content of 11.1 mg ml^-1 and cellulose content of 0.41 mg g^-1. Saccharification by malting increased reducing sugar content by 77.9% (19.75 mg ml^-1). The optimum fermentation conditions (pH, temperature and incubation period) for Z. mobilis and S. cerevisiae were 5.5, 35°C, 3 days and 6.0, 30°C, 4 day, respectively. The maximum ethanol yield of 3.03 g l^-1 and efficiency of 62% were obtained for S. cerevisiae while yield of 3.63 g l^-1 and efficiency of 74.2% were obtained for Z. mobilis. Z. mobilis conclusively may be better organism for ethanol production from pito mash.

Keywords: Pito mash, agro-industrial wastes, Zymomonas mobilis, ethanol, reducing sugars