Method for the production of xylitol

DETAILED DESCRIPTION The present invention contemplates a method for the production of substantially pure xylitol from an aqueous xylose solution which may also contain hexoses such as glucose as well as other impurities.
The invention contemplates fermenting said solution using a yeast strain capable of converting substantially all of said free xylose to xylitol and most of said free hexoses to ethanol.
The fermented product is purified by removing yeast cells from the solution by filtration, centrifugation or other suitable expedients and removing ethanol by evaporation or distillation.
Chromatographic separation yields a xylitol rich fraction or fractions from which xylitol can be crystallized.
In some cases, pretreatment of the aqueous xylose solution is utilized.
Such pretreatment may include posthydrolysis and/or separation steps in order to remove components which may be toxic and/or harmful to the yeast used to convert the xylose to xylitol or other impurities which may adversely affect the subsequent fermentation and separation steps.
Such pretreatment steps can include chromatographic separation techniques.
The present invention utilizes yeasts capable of reducing xylose to xylitol and hexoses to ethanol.
Such yeasts include, but are not limited to, yeasts of the genus candida, pichia, pachysolen and debaryomyces.
Of these genera, Candida and Debaryomyces are preferred with Candida tropicalis and Debaryomyces hansenii being particularly preferred.
One good example is the Candida tropicalis strain deposited in the American Type Culture Collection and assigned Accession Number 9968.