Xylitol from low-cost substrate and process optimization

Abstract

Xylitol is a high-quality polyalcohol, mainly used in pharmaceuticals, hygiene products, and food due to its functional properties such as anticarcinogenic, antibacterial, low-calorie, and hypoglycemic properties. At present, xylitol is primarily produced through chemical hydrogenation of xylose at high temperatures (150 °C) and pressure (5.5 MPa) on the reaction with metal catalysts such as Pl, Ru, Pt and Raney nickel. Separation and purification of xylitol is very expensive through this process. However, compared to this method, xylitol production through bioconversion of hemicellulosic hydrolysate by micro-organisms is an environment friendly, less energy-intensive, renewable, and overall economical process. This process ensures high safety, low production cost and high product selectivity. The primary objective of this research is to utilize the agricultural bio-waste (such as areca nut husk) as a feedstock for the production of xylitol, preferably in a repetitive batch fermentation process, with C. tropicalis as the fermentative microorganism. Primary processes include, biomass characterization and pretreatment (Mainly dilute acid hydrolysis and lime treatment), Acidic and Enzymatic hydrolysis of biomass, detoxification of acidic hydrolysate by using activated charcoal and cation-anion exchange resins, detoxified hydrolysate was fermented by C. tropicalis for xylitol production and finally downstream process was performed for product purification. Lignocellulosic materials are inexpensive and readily available biomass in the form of either agricultural wastes or forest residues. These materials can be used as energy producer sources for solids (xylitol, etc.) liquids (ethanol, butanol, etc.) and gaseous (CO, H2, etc.) as energy to meet increasing energy demands. Biomass pretreatment is a predetermined step to fragment lignocellulosic biomass into its basic components such as lignin and carbohydrate molecules. The first objective of present study is the pretreatment and characterization of lignocellulosic biomass namely Areca nut husk (Arecan catechu), which is widely available in the region of North-Eastern part of India. The study includes several physical characterizations like ultimate and proximate analysis, thermogravimetric analysis, crystallinity and chemical characterization that embraced Raman spectroscopy and FTIR. This study revealed that the Areca husk fiber contained 29.17% hemicellulose. Combination of all these properties revealed that Areca nut husk can be explored as the impending potential for low-cost source of xylose.