Biological production and downstream separation of xylitol using Candida tropicalis.

Xylitol is one of the platform chemicals identified by the U.S. Department of Energy as a promising candidate for production from biomass. It is an important chemical building block with applications in both the food and pharmaceutical industries. Xylitol is a pentose sugar alcohol with low caloric value, anti-cariogenic properties, and some ability to inhibit microbial growth. The objective of this work is to identify new routes for production of xylitol from lignocellulosic biomass with a focus on post-fermentation downstream processing and separation. Fermentation (via C. tropicalis) conditions including varied initial xylose concentrations (10 and 30 g L-1) and different pH control methodologies (with sodium hydroxide and PBS buffer or without adjustment) were evaluated. An initial xylose concentration of 10 g L-1 with pH control using sodium hydroxide resulted in the highest xylitol yield of 75%. Amberlite IRC 748, a commonly used cationic resin for wastewater treatment, was used to develop an ion-exchange chromatographic separation for the xylitol from fermentation hydrolysates, with the intention to then concentrate and crystallize the xylitol. It was determined that three consecutive water washes were able to selectively recover xylitol from the ion-exchange column with 45% of the recovered xylitol concentrated in the second water wash at even low retention times of 1 minute. Future work may include comprehensive techno-economic analyses, comparisons of different feedstocks, and a life cycle assessment of the xylitol biorefinery.