High alcohol production by repeated batch fermentation using an immobilized osmotolerant Saccharomyces cerevisiae

A repeated batch fermentation system was used to produce ethanol using an osmotolerant Saccharomyces cerevisiae (VS3) immobilized in calcium alginate beads, For comparison free cells were also used to produce ethanol by repeated batch fermentation. Fermentation was carried for six cycles with 125, 250 or 500 beads using 150, 200 or 250 g glucose L-1 at 30 degrees C, The maximum amount of ethanol produced by immobilized VS, using 150 g L-1 glucose was only 44 g L-1 after 48 h, while the amount of ethanol produced by free cells in the first cycle was 72 g L-1. However in subsequent fed batch cultures more ethanol was produced by immobilized cells compared to free cells. The amount of ethanol produced by free cells decreased from 72 g L-1 to 25 g L-1 after the fourth cycle, while that of immobilized cells increased from 44 to 72 g L-1, The maximum amount of ethanol produced by immobilized VS, cells using 150, 200 and 250 g glucose L-1 was 72.5, 93 and 87 g ethanol L-1 at 30 degrees C.