Bioethanol production by a flocculent hybrid, CHFY0321 obtained by protoplast fusion between Saccharomyces cerevisiae and Saccharomyces bayanus

Fusion hybrid yeast, CHFY0321, was obtained by protoplast fusion between non-flocculent-high ethanol fermentative Saccharomyces cerevisiae CHY1011 and flocculent-low ethanol fermentative Saccharomyces bayanus KCCM12633. The hybrid yeast was used together with the parental strains to examine ethanol production in batch fermentation. Under the conditions tested, the fusion hybrid CHFY0321 flocculated to the highest degree and had the capacity to ferment well at pH 4.5 and 32 °C. Simultaneous saccharification and fermentation for ethanol production was carried out using a cassava (Manihot esculenta) powder hydrolysate medium containing 19.5% (w v−1) total sugar in a 5 l lab scale jar fermenter at 32 °C for 65 h with an agitation speed of 2 Hz. Under these conditions, CHFY0321 showed the highest flocculating ability and the best fermentation efficiency for ethanol production compared with those of the wild-type parent strains. CHFY0321 gave a final ethanol concentration of 89.8 ± 0.13 g l−1, a volumetric ethanol productivity of 1.38 ± 0.13 g l−1 h−1, and a theoretical yield of 94.2 ± 1.58%. These results suggest that CHFY0321 exhibited the fermentation characteristics of S. cerevisiae CHY1011 and the flocculent ability of S. bayanus KCCM12633. Therefore, the strong highly flocculent ethanol fermentative CHFY0321 has potential for improving biotechnological ethanol fermentation processes.