Production of Bioethanol from Hydrolysed Cocoyam (Colocasia Esculenta ) by Thermotolerant Saccharomyces Cerevisiae

Abstract

Production of bioethanol from hydrolysed cocoyam substrates by thermotolerant S. cerevisiae was investigated. Thermotolerant S. cerevisiae was selected based on its ethanol production activity, the yeast was able to produce an ethanol yield of 3.66% and 2.84% at 37OC and 40OC respectively, when innoculated into YPD medium for a period of 72 hrs. Optimization studies were carried out as different nitrogen sources were added to the fermentative medium. The medium with a combination of yeast extract and peptone gave the highest ethanol yield (5. 89%) and reducing sugar (46.8mg/ml). The lowest ethanol yield (2.75%) and reducing sugar (18.7 mg/ml) was observed in the medium where ammonium sulphate was added after 5 days of fermentation. The effect of different glucose concentrations was studied and the highest ethanol yield (5. 61%) and reducing sugar (46.9 mg/ml) was observed in the medium containing 5% glucose. The lowest ethanol yield (1.03%) and reducing sugar (28.5 mg/ml) was observed in the medium supplemented with 1% glucose. The effect of pH was also studied and revealed that pH 4. 5 is the optimum pH for ethanol production with (4. 83%) ethanol yield and (41.7mg/ml) reducing sugar. The lowest ethanol yield (2.92%) and reducing sugar (29.6mg/ml) was observed in the medium adjusted to pH 3.5. Fermentation carried out combining the best parameters from the optimization studies produced an ethanol yield of 6.88% and reducing sugar of 72.5mg/ml at the end of fermentation, there was an increase in ethanol yield and reducing sugar when compared with previous experiments conducted. The optimization studies revealed that the initial rate of ethanol yield by fermentation of the hydrolysed substrate with S. cerevisiae SCPW 11 can be enhanced by adding 5% glucose as carbon source, a combination of yeast extract and peptone as nitrogen sources at temperature 30oC and pH 4.5. This study has demonstrated the potential of cocoyam as a suitable substrate for ethanol production.