Bioproduction of xylitol by Candida tropicalis 13803 from pistachio shell hydrolysate obtained through MW-HPCO2 system

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Objective: Biotechnological xylitol production from secondary agricultural residues is a promising approach for a sustainable and environmental purpose. Lignocellulosic biomass is a significant feedstock for biofuel and biochemical production. Its accessibility, cost-effectiveness, renewability, and environmental friendliness make it an attractive alternative to fossil fuels and other conventional sources of energy and chemicals. Materials and methods: In this study, the conversion of xylan to xylose in a pistachio shell was provided with a novel technology of a microwave-assisted high-pressure CO2/H2O system. Xylose rich pistachio shell hydrolysate was utilized by Candida tropicalis ATCC 13803 for xylitol production. Different concentrations of xylose (50, 100, and 150 g/L) were employed for xylitol production in shake-flask. Results and conclusion: HMF and furfural were completely removed from xylose-rich hydrolysate by activated charcoal. The improvement in yeast performance was limited with increasing xylose concentration. The highest xylitol produced by C. tropicalis from pistachio shell hydrolysate (65.15 g/L) and the maximum yield of xylitol 0.66 g/g with 100 g/L xylose were obtained in shake-flask whereas xylitol produced at 50 g/L and 150 g/L xylose were 0.65 and 0.37 g/g, respectively. Volumetric productivity at 100 g/L of xylose was 1.28 times and 1.84 times higher compared to xylose concentrations of 50 g/L and 150 g/L, respectively. Xylitol production performance (71.73 g/L) of detoxified pistachio shell hydrolysate at 100 g/L of xylose was almost identical to pure xylose. However, the yeast was not able to consume xylose at 150 g/L resulting in no xylitol production.