A sustainable approach for xylitol production from pistachio shell using Candida tropicalis

This study presents a novel approach for producing xylitol from xylose-rich hydrolysate derived from pistachio shells. Initially, xylose-rich hydrolysate was obtained through microwave-assisted high-pressure CO₂/H₂O hydrolysis, achieving a maximum xylose concentration of 14.58 ± 0.11 g L⁻¹ and yield of 62.01 ± 0.92% (w w⁻¹). Prior to the bioconversion process, the hydrolysate was detoxified using activated charcoal to remove inhibitory compounds such as hydroxymethylfurfural (HMF) and furfural. Xylitol production from the detoxified hydrolysate was carried out biotechnologically using the yeast Candida tropicalis. A Box–Behnken design was implemented to investigate the effect of temperature, pH, and aeration rate on xylitol yield during bioconversion in bioreactor. The highest xylitol yield of 0.94 g g⁻¹ was recorded at 72 h under optimized conditions of 34.5 °C, pH 4.5, and 1.2 vvm. Recovery and purification of xylitol from the fermentation medium was achieved using ethanol as an antisolvent. Xylitol was recovered with a yield of 68.4% from culture medium by crystallization. Based on the findings of this study, a sustainable and environmentally friendly process can be proposed for recovering and purifying xylitol from pistachio shell hydrolysate.