Factors affecting ethanol fermentation using Saccharomyces cerevisiae BY4742

Fermentation of sugar by Saccharomyces cerevisiae BY4742, for production of ethanol in a batch experiment was conducted to improve the performance of the fermentation process. The thermotolerant ability of S. cerevisiae to grow and ferment glucose at elevated temperatures similar to the optima for saccharification was investigated. The influences of temperature, substrate concentration and pH on ethanol fermentation were observed. The yield for ethanol production and changes in the fermentation pathway were compared under different conditions. When the temperature was increased to 45 °C, the system still showed high cell growth and ethanol production rates, while it was inhibited at 50 °C. The maximum specific growth rate and the maximum specific ethanol production rate were observed between 30 and 45 °C with different initial glucose concentrations. The maximum sugar conversion at 30 °C after 72 h incubation was 48.0%, 59.9%, 28.3%, 13.7% and 3.7% for 20, 40, 80, 160 and 300 kg m−3 of glucose concentrations respectively. Increased substrate supply did not improve the specific ethanol production rate when the pH value was not controlled. pH 4.0–5.0 was the optimal range for the ethanol production process. The highest specific ethanol production rate for all the batch experiments was achieved at pH5.0 which is 410 g kg−1 h−1 of suspended solids (SS) which gave an ethanol conversion efficiency of 61.93%. The highest specific ethanol production rate at 4.0 was 310 g kg−1 h−1 of SS. A change in the main fermentation pathway was observed with various pH ranges. Formation of acetic acid was increased when the pH was below 4.0, while butyric acid was produced when the pH was higher than 5.0. In the presence of oxygen, the ethanol could be utilized by the yeast as the carbon source after other nutrients became depleted, this could not occur however under anaerobic conditions.