Optimization of ethanol production from carob pod extract using immobilized Saccharomyces cerevisiae cells in a stirred tank bioreactor

Abstract

In this study, optimization of ethanol production from carob pod extract was carried out by immobilized Saccharomyces cerevisiae. Results showed that Ca-alginate concentration and the amount of immobilized cells had significant effects on yield. Optimum conditions for ethanol fermentation were determined to be 2% Ca-alginate concentration, 150rpm agitation rate, 5% yeast cells entrapped in beads and pH 5.5. After validation experiments; ethanol concentration, yield, production rate and sugar utilization rate were respectively 40.10g/L, 46.32%, 3.19g/L/h and 90.66%; and the fermentation time was decreased to 24h. In addition, the immobilized cells were shown to be reusable for five cycles, though a decrease in yield was observed. Finally, carob pod extract was used for ethanol fermentation by controlled and uncontrolled pH without any enrichment, and the results suggest that carob extract can be utilized effectively by immobilized-cell fermentation without the use of enrichments to facilitate yeast growth.