In order to improve the fermentative efficiency of sugar maple hemicellulosic hydrolysates for fuel ethanol production, various methods to mitigate the effects of inhibitory compounds were employed. These methods included detoxification treatments utilizing activated charcoal, anion exchange resin, overliming, and ethyl acetate extraction. Results demonstrated the greatest fermentative improvement of 50% wood hydrolysate (v/v) by Pichia stipitis with activated charcoal treatment. Another method employed to reduce inhibition was an adaptation procedure to produce P. stipitis stains more tolerant of inhibitory compounds. This adaptation resulted in yeast variants capable of improved fermentation of 75% untreated wood hydrolysate (v/v), one of which produced 9.8 g/l ± 0.6 ethanol, whereas the parent strain produced 0.0 g/l ± 0.0 within the first 24 h. Adapted strains RS01, RS02, and RS03 were analyzed for glucose and xylose utilization and results demonstrated increased glucose and decreased xylose utilization rates in comparison to the wild type. These changes in carbohydrate utilization may be indicative of detoxification or tolerance activities related to proteins involved in glucose and xylose metabolism.

In an effort to devise inexpensive and sustainable production of ethanol fuel, experiments were conducted to establish conditions for Pichia stipitis NRRL Y-7124 to ferment a membrane treated wood hydrolysate derived from sugar maple to produce ethanol. The degree of aeration required to effectively utilize xylose, produce ethanol, and minimize xylitol formation as well as the optimal hydrolysate concentration were the conditions examined. P. stipitis produced the highest concentrations of ethanol in shake flasks at 150 rpm (14.3 g/L in 71 h), and 50% hydrolysate maximized ethanol yield (12.4 g/L in 51.5 h). In the 50% hydrolysate cultures, P. stipitis produced ethanol at a rate of 0.24 g/L×h with a yield of 0.41 g ethanol/g wood-derived carbohydrate.