Xylitol production from prehydrolysis liquor of kraft-based dissolving pulp by Candida tropicalis

Abstract

Xylitol production from the hemicelluloses of prehydrolysis liquor (PHL) is of practical interest from both economic and environmental standpoints. The removal of the inhibitors, e.g., lignin, acetic acid, and furfural, is the key to improving the conversion of xylose to xylitol when Candida tropicalis fermentation is used. For this purpose, a full chain process involving activated carbon adsorption, ion exchange resin treatment, acidolysis, and fermentation was considered in this work. The results showed that 72.6% of lignin and 67.1% of furfural were removed using an activated carbon dosage of 20 mg/g PHL. Additionally, 61.2% of acetic acid was also removed at a resin dosage of 100 mg/g PHL. Subsequently, acidolysis using sulfuric acid and pH adjustment with lime was performed on the treated PHL to convert the oligosaccharides into monosaccharides; a yield of 0.40 g xylitol/g xylose was achieved via treating the PHL with Candida tropicalis fermentation at 30 °C, 200 rpm, and 96 h. In addition, a material balance was determined for the full chain process.

Current advances in Candida tropicalis: Yeast overview and biotechnological applications

“…Strategies have been investigated to enhance xylitol production by C. tropicalis, such as cellular adaptation, immobilization, controlling glucose/xylose ratio, fed-batch fermentation, and among others. 47,48 Cellular adaptation is an approach used to overcome the inhibitory effect of toxic compounds released in the treatment of lignocellulosic biomasses. This technique consists in cultivating the microorganism in the fermentation medium, such as hemicellulosic hydrolysates, for successive cycles.…”