Fermentation of High Gravity Glucose by Free and Immobilized saccharomyces cerevisiae S1 by Cell Recycling

Abstract

The potential economic benefits in ethanol production could be realized by conducting fermentation at 40o C and above. In this study, thermotolerant yeast isolated and developed in our laboratory was used in the cell recycle operations to find the possibility to improve the high gravity fermentation. Fermentation of glucose (300 gL-1)−PYN medium by free and agar immobilized Saccharomyces cerevisiae S1 cells took 36 h to utilize glucose completely and produced 100 and 143 gL-1 ethanol, respectively. When the free and agar immobilized Saccharmyces cerevisiae S1 cells were subjected to repeated batch operation in glucose (300 gL-1)−PYN medium, it was possible to continue the process with 2 and 37 cycles respectively. When the free cells were used in the repeated batch fermentation with glucose (300 gL-1)−2PYN medium supplemented with 26.8 gL-1 soy flour, it was possible to continue the process for 7 repeated cycles. However, stuck fermentation was observed with advancing cycles with increasing residual sugar with free cells. Thus, cell recycle batch process was possible with additional nutrients in the medium while with immobilized cells such additional nutrients were not necessary.