Direct saccharification and ethanol fermentation of cello-oligosaccharides with recombinant yeast

Ethanol was produced at good rates by direct saccharification and fermentation of cello-oligosaccharides with pYBGA1 yeast, a recombinant laboratory yeast expressing β-glucosidase. Cellobiose in the concentration of 50 g/L was directly fermented for 60 h with 1 × 108 cells/mL of pYBGA1 yeast at 30 °C to give ethanol at an 80% theoretical conversion rate and a concentration of more than 20 g/L of concentration. Conversion to ethanol increased with increasing cellobiose concentration in the feed. When cellobiose was used at the concentration of 100 g/L, ethanol conversion and concentration increased to 85% and 45 g/L, respectively, in 96 h incubation. Other cello-oligosaccharides, cellotriose, cellotetraose, and cellopentaose at the concentration of 50 g/L, respectively, were also fermented directly for 72 h with 1 × 108 cells/mL of pYBGA1 yeast to produce ethanol in the conversion rates and concentrations of 71–73% and 18.0–18.5 g/L, respectively. The direct saccharification and fermentation mechanism of cello-oligosaccharides with pYBGA1 yeast, as revealed by HPLC measurements, suggesting that cellotetraose, for example, was saccharificated to cellotriose, cellobiose, and glucose and then fermented to give ethanol. These results suggest that the direct saccharification and fermentation of cello-oligosaccharides with pYBGA1 has several advantages as a simple procedure and for time, cost, and energy consumptions.