Xylitol production from rapeseed straw hemicellulosic hydrolysate

Rapeseed straw is an agricultural residue whose production has increased in recent years due to growing interest in rapeseed oil for biodiesel production. The rapeseed straw fractionation under suitable conditions allows obtaining a xylose rich hemicellulosic hydrolysate. The aim of this study was to evaluate the fermentability of a concentrated hemicellulosic hydrolysate produced from rapeseed straw, by the yeasts Debaryomyces hansenii NRRL Y-7426 and Candida guilliermondii FTI 20037 (ATCC 201935). Before fermentation, different detoxification strategies were performed and compared in order to reduce the concentration of toxic compounds present in the hydrolysate. The fermentation performance was also compared for all the cases. According to the results, the hydrolysate produced from rapeseed straw hemicellulose is potentially fermentable to xylitol by both yeasts. However, C. guilliermondii was more tolerant to the presence of toxic compounds, especially acetic acid. Such behaviour makes this yeast particularly more attractive for use in this bioprocess since it requires less steps of detoxification previous the hydrolysate use as fermentation medium. In addition, it was not necessary to supplement the hydrolysate with nutrients, which brings additional economic advantages to the process. Previous adaptation of the yeast to the hydrolysate was also not required when the toxic compounds were present in reduced concentration.