Xylitol Production by Candida Species from Prairie Cordgrass Hydrolysate

摘要

Xylitol can be naturally isolated at high cost from the fibers of many fruits or vegetables and its applications include being used as an alternative sweetener or food additive. This investigation explored microbial xylitol production from hydrolyzed plant biomass to learn if a more economical process to produce the sugar alcohol xylitol could be developed. With strains of the yeast Candida able to produce xylitol after growth on a xylose-containing medium or on a hemicellulose hydrolysate of a native North American prairie grass, Candida mogii ATCC 18364 as well as Candida guilliermondii ATCC 20216 and ATCC 201935 were used in this study to analyze xylitol production from buffered prairie cordgrass hydrolysates. To prepare the hydrolysate, the grass was suspended in 0.5% (w/v) potassium phosphate buffer pH 4.5, 5.0, 5.5, or 6.0 and then treated using high pressure and temperature. The resultant solids were hydrolyzed using the enzyme xylanase and the xylitol levels present were measured spectrophotometrically. All Candida strains produced the highest xylitol levels when grown on the pH 5.5 phosphate-buffered hydrolysate for 120 or 168 h at 30 ?C. Biomass production by ATCC 201935 was 1.3-fold higher than ATCC 18364 after growth for 120 h at 30 °C while ATCC 201935 produced a 1.3-fold higher biomass level than did ATCC 18364 after 168 h of growth. ATCC 18364 produced a 1.1-fold higher xylitol yield than did ATCC 201935 after growth for 120 h at 30 °C and produced a 1.1-fold higher xylitol yield than did ATCC 201935 after growth for 168 h. Overall, xylitol production by the strains tested was dependent on the pH utilized to buffer the cordgrass hydrolysates and how long that they were grown on the hydrolysate.