Xylitol Production by Candida Species from Hydrolysates of Agricultural Residues and Grasses

Thomas P. West

doi:10.3390/fermentation7040243

Abstract

Xylitol is an industrially important chemical due to its commercial applications. The use of xylitol as a sweetener as well as its utilization in biomedical applications has made it a high value specialty chemical. Although several species of yeast synthesize xylitol, this review focusses on the species of the genus Candida. The importance of the enzyme xylitol reductase present in Candida species as it relates to their ability to synthesize xylitol was examined. Another focus of this work was to review prior studies examining the ability of the Candida species to synthesize xylitol effectively from hydrolysates of agricultural residues and grasses. An advantage of utilizing such a hydrolysate as a substrate for yeast xylitol production would be decreasing the overall cost of synthesizing xylitol. The intent of this review was to learn if such hydrolysates could substitute for xylose as a substrate for the yeast when producing xylitol. In addition, a comparison of xylitol production by Candida species should indicate which hydrolysate of agricultural residues and grasses would be the best substrate for xylitol production. From studies analyzing previous hydrolysates of agricultural residues and grasses, it was concluded that a hydrolysate of sugarcane bagasse supported the highest level of xylitol by Candida species, although corncob hydrolysates also supported significant yeast xylitol production. It was also concluded that fewer studies examined yeast xylitol production on hydrolysates of grasses and that further research on grasses may provide hydrolysates with a higher xylose content, which could support greater yeast xylitol production.

Highlights

IntroductionThe industrially important specialty chemical xylitol, whose annual commercial production is approaching 40,000 tons [1], has several commercial applications (Figure 1)
The industrially important specialty chemical xylitol, whose annual commercial production is approaching 40,000 tons [1], has several commercial applications (Figure 1).The highest value commercial application for xylitol use is as an alternate sweetener in such products as chewing gum and various foods including ice cream and candy [2].Beyond its utilization as a sweetener, biomedical applications exist for xylitol, including being used to prevent ear inflammations and its ability to stimulate murine hybridoma cell production [3,4,5]
A number of investigations have examined the ability of Candida species to utilize hydrolysates of agricultural residues and grasses to support xylitol synthesis

Summary

Introduction

The industrially important specialty chemical xylitol, whose annual commercial production is approaching 40,000 tons [1], has several commercial applications (Figure 1). Low-value biomass residues are excellent candidates for the large-scale production of xylitol Such low-cost residues are readily available as a raw material for xylitol synthesis compared to the process components used during the chemical bioconversion of xylose into xylitol. This could include utilizing hydrolysates of agricultural residues or hydrolysates derived from various species of grasses [11,12,13,14,15,16]. Prior work has identified a number of Candida species that are able to synthesize xylitol from the xylose present in hydrolyzed agricultural residues or grasses [17,18,19,20,21]. The findings indicated which type of biomass has the greater potential for large-scale biobased xylitol synthesis

Pathway of Xylitol Biosynthesis in the Yeast Candida

Xylitol Production by Candida Species from Agricultural Residues

Xylitol Production by Candida Species from Grasses

Findings

Conclusions