Li Fu Chen

Quantitative production of xylitol from D-xylose by a high-xylitol producing yeast mutant Candida tropicalis HXP2

SummaryXylitol was produced as a metabolic by-product by a number of yeasts when grown on medium containing D-xylose as carbon and energy sources. Among the yeast strains tested, a mutant strain of Candida tropicalis (HXP2) was found to produce xylitol from D-xylose with a high yield (>90%). Ethanol was also produced by HXP2 when D-glucose, D-fructose, or sucrose were used as substrates. The high-xylitol-producing yeast mutant is a good organism for the production of xylitol from biomass that contains D-xylose.

Conversion of hemicellulose carbohydrates

Hemicellulose can be converted to a variety of useful products. There are two approaches to hemicellulose bioconversion; hemicellulose can be directly converted, or the hemicellulose-derived carbohydrates can be used as the substrate. The major problem in the bioconversion of hemicellulose carbohydrates is that suitable organisms which convert pentoses efficiently have not been developed. The advantage of bacterial processes is that a diverse range of products can be formed. The advantages of the yeast process is that specific products such as ethanol and polyols can be produced in high yields. The understanding of metabolic pathways and metabolic regulation is important for the improvement of existing microbial strains or the development of new strains. The use of yeasts to produce ethanol from d-xylose through isomerization of d-xylose to d-xylulose and the prospects for future developments in biomass conversion are discussed.