Abstract
Bioethanol was produced from agricultural residues in Hokkaido Prefecture, Japan, by dilute alkali pretreatment, and then successive saccharification with cellulase and fermentation with recombinant yeast pYBGA1 that is a recombinant laboratory yeast expressing β-glucosidase. The agricultural residues, beet pulp, beet leaf, corn stover, and weed were pretreated with 2% NaOH aqueous solution for 1 h at 121℃ to remove lignin. The pretreated beet pulp (20 g/L), for example, was then saccharified for 24 h by Cellic CTec (10 wt% to beet pulp) as the cellulase at 50℃ to give glucose (11.8 g/L) at relatively good rates. After the temperature decreased to 30℃, the resulting glucose was continuously fermented for 36 h by addition of 1 × 108 cells/mL of pYBGA1 yeast to give 5.54 g/L of bioethanol in 60% and 92% theoretical yields of cellulose in beet pulp and glucose saccharified, respectively. Other agricultural residues also afforded bioethanol by the successive saccharification and fermentation. It was found that the appropriate cellulase for saccharification differed with the kind of agricultural residue; beet pulp was effectively saccharified by Cellic CTec, beet leaf and corn stover by Sucrose C, and weed by Sumizyme C. These agricultural residues were found to be suitable for the production of bioethanol because Hokkaido Prefecture is the most abundant producer of beets and corn in Japan, and accordingly, agricultural residues are easily available. pYBGA1 was also found to be a good yeast for the fermentation of sugars saccharified from agricultural residues.
