Aqueous solutions of deep eutectic systems as reaction media for the saccharification and fermentation of hardwood xylan into xylitol

Abstract

The aim of this study was to evaluate the effect of aqueous solutions of deep eutectic solvent, Cholinium Chloride:Urea ([Ch]Cl:U) at50wt%and20 wt%,using differentmolar ratios(1:1, 2:1and 1:2)onthe enzymatic hydrolysis ofxylanforxyloseproduction anditssubsequent bioconversion into xylitolusing arecombinant yeast strain. The lowest xylan conversion into xylose (45%) was obtained using 1:2 [Ch]Cl:U molar ratio. On the other hand, the 1:1 [Ch]Cl:U molar ratio, at 20 wt% in water, improved this conversion, achieving the highest xylose yield (81.4%). The xylitol production was then optimized with [Ch]Cl:U (1:1) at 20 wt% by simultaneous saccharification and fermentation process, attaining 23.67 g/L, corresponding to 66.04% of xylitol yield. This study reveals the possibility of using xylan solubilized in DES aqueous solutions directly for xylitol production, thus assembling a one-step process.