Detoxification procedures of eucalyptus hemicellulose hydrolysate for xylitol production by Candida guilliermondii

Abstract

Xylitol can be obtained from hemicelullosic fraction of lignocellulosic materials containing d-xylose. A problem associated with the fermentation of hemicellulosic sugars to xylitol is the presence of a broad range of compounds, which inhibit the fermenting microorganisms. These inhibitors can be removed from the hydrolysate by a detoxification method, prior to fermentation. This study describes different detoxification methods of eucalyptus residues hydrolysate to improve xylitol production by Candida guilliermondii. The changes in the concentrations of fermentable sugars and four groups of inhibitory compounds were determined and the fermentability of detoxified hydrolysates was assayed. The applied detoxification methods include: treatment with active charcoal and four different resins (cationic and anionic) in sequence. Ion exchange resins were more efficient than activated charcoal to remove all four major groups of inhibitory compounds without sugar loss. The ion exchange detoxification drastically enhanced the fermentability of the hydrolysate. Under the best assayed operating conditions, 32.7 g/L of xylitol were achieved after 48 h fermentation, which correspond to 0.68 g/L h volumetric productivity and 0.57 g/g xylitol yield factor. In addition, it was verified that low concentrations of acetic acid can have a benefical effect on xylitol productivity.