Bioethanol production from two varieties of mango kernel using co-culture of <i>Bacillus subtilis, Aspergillus niger</i> and <i>Saccharomyces cerevisiea</i>

Abstract

Production of bioethanol from solid waste such as mango kernel using microbial culture is an attractive option for waste management and substitute for fossil fuel. This study was carried out to produce ethanol from two varieties of mango kernel using cultures of Aspergillus niger, Bacillus subtilis and Sacchromyces cerevisiae isolated from soil, fermented African locust bean (daddawa), palm wine respectively. The isolates were identified and confirmed using phenotypic identification techniques. The proximate composition of the mango kernels were evaluated using AOAC (2012) methods. The mango kernels ground into powder were subjected to enzymatic hydrolysis using co-culture of B. subtilis and A. niger. Analysis of reducing sugar residue was performed using Dinitrosalicyclic acid (DNS). Fermentation of the hydrolysates was carried out for 96 hours and the ethanol produced was quantified. The optimum conditions for ethanol production such as pH, temperature, substrate concentration and time of fermentation were determined. The proximate analysis revealed carbohydrate contents of 50.79% and 52.54% in Banginapalli and Benue mangoes, respectively. There is no significant difference (p>0.05) in the proximate composition of the mango kernels. The enzymatic hydrolysis revealed the reducing sugar content of 5.36g/L in Benue mango and 5.34g/L in Banginapalli mango after 5 days of hydrolysis. The fermentation of the hydrolysate of Benue mango yielded the highest quantity of ethanol (19.15%) with a fermentation efficiency of 37.47% after 72 hours fermentation. The results of optimization revealed that pH 4.5, temperature of 30^oC, 30g substrate concentrations and fermentation period of 72 hours were the optimum condition for production of the bioethanol. The result of this work has shown that the two varieties of mango could serve as good raw materials in the production of bioethanol, thereby turning the mango waste to potential wealth

Keywords: Bioethanol, Fermentation, Substrate, Waste.