초록
Two strains of each yeast Candida shehatae and Pichia stipitis were used to ferment sugar maple wood extracts to ethanol. Of these four strains the most promising was the P. stipitis NRRL Y-11543 strain. This strain produced a maximum of 13.51 g L<SUP>-1</SUP> ethanol from wood extracts containing 5- and 6- carbon sugars. The main carbon source for fermentation in these extracts was xylose monosaccharide at 36.7 g L<SUP>-1</SUP> with other sugars concentrations ranging from 1.04 to 2.08 g L<SUP>-1</SUP>. Through dilute acid hydrolysis the oligomers in the extracts were converted to xylose and other monosaccharides. The initial sugar maple dilute acid hydrolysate used in this study has a xylose concentration of 86.8 g L<SUP>-1</SUP>. Nano-membrane filtration removed the majority of the acetates, formates, furfurals and methanol, which were liberated during hydrolysis; however the sulfates that were introduced remained. High levels of sulphate and aromatic compounds in the hydrolysate were inhibitory to the fermentation. P. stipitis did not produce much ethanol from this hydrolysate without dilution with distilled water. The highest ethanol concentration reached was 18.4 g L<SUP>-1</SUP> after a 1:1 dilution with distilled water. Further improvements in the hydrolysis of hot water extracts also resulted in higher sugars concentrations. Reducing the amount of sulfates as well as better control of aeration rate by carrying out the fermentation in a benchtop fermentor resulted in higher ethanol concentrations of 35.4 g L<SUP>-1</SUP> in only 76 h as opposed to 7 days in shake flasks.