Submitted to: Applied Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 9, 1996
Publication Date: N/A
Interpretive Summary: Corn-based fuel ethanol production generates large volumes of low- value byproducts, often marketed as animal feed supplements based upon their protein value. Certain of these materials also retain potentially valuable carbohydrates, including five-carbon sugars such as xylose. In order to offset the relatively high cost of corn feedstocks, we sought to develop new value-added co-products from fuel ethanol residues. Xylitol is a natural, anticariogenic sweetener (sugar substitute) used in such products as chewing gum, toothpaste and mouthwashes. Although xylitol is currently produced by chemical catalysis of xylose from wood fiber, biocatalysis of corn fiber (an abundant source of xylose) may be an attractive alternative. We examined xylitol production by the yeastlike fungus, Pichia guilliermondii. One strain from the ARS Culture Collection, NRRL Y-12723, was identified as a promising organism for bioconversion of xylose to xylitol. This work should be of interest to fuel ethanol producers looking for new co-product markets to enhance the economic competitiveness of their industry, and should in turn benefit farmers by providing expanding markets for corn products.
Seven strains of Pichia guilliermondii (=Candida guilliermondii, asexual state) from diverse isolation sources were examined for the production of xylitol and riboflavin in xylose-grown cultures. Under conditions tested, all strains produced xylitol from xylose; optimal conversion efficiencies varied on a strain-specific basis, from 7-36% of initial substrate. Four of seven strains reutilized xylitol immediately as xylose and xylitol levels became equal. The remaining three strains metabolized xylitol slowly and incompletely. Surprisingly, reutilization of xylitol showed an apparent relationship with riboflavin production. The four strains that rapidly reutilized xylitol produced up to six-fold greater levels of riboflavin than did strains that slowly used xylitol. Moreover, riboflavin accumulation took place during xylitol consumption.