Preliminary evaluation of sensitivity of <i>Saccharomyces cerevisiae</i> LC 269108 to thermal and ethanol stresses in fermentation of agro-wastes for bioethanol production

Abstract

The effect of two temperature regimes and ethanol accretion on the ethanolegenic characteristic of Saccharomyces cerevisiae LC 269108 was investigated in shaker flask experiments using flour processed from dried yam peels as feedstock. The flour was initially liquefied in boiling water before enzymatic pretreatment using amyloglucosidase, cellulase and pectinase. To 20% (w/v) of the gelatinized syrup was added 0.5 ml of nitrogen base and 1 ml of standardized overnight suspension of the culture. Fermentation was carried out for 60 h at 120 rpm, pH of 5.5 and temperature of 30 and 40 °C. A 5% (v/v) ethanol was included in a separate batch and fermented as described. Results show that ethanol concentration increased at both temperature conditions as well as in the batch supplemented with ethanol. Glucose decreased from initial concentration of 9.63 ± 0.34% until it was completely exhausted from the system. At 30 °C, peak concentration of ethanol (5.30 ± 0.2%) was achieved after 24 h. However, at 40 °C the highest ethanol content (5.61 ± 0.57%) was reached after 48 h. No difference (p < 0.05) was found between the concentration of ethanol produced at the two temperature states. In the batch augmented with ethanol (5%), peak production (4.41 ± 0.20%) was reached after 24 h at both 30 and 40 °C. Subsequently, ethanol concentration maintained plateau at 30 °C but in the batch incubated at 40 °C, it dropped steadily after 24 h until reaching final concentration of 3.93 ± 0.25% after 60 h. The yeast displayed promising attributes which can be harnessed for future developments in high temperature ethanol fermentation.