Enhanced Xylitol Production from Statistically Optimized Fermentation of Cotton Stalk Hydrolysate by Immobilized Candida tropicalis

Cotton (Gossypium hirsutum), which is one of the most abundant crops in the world, is cultivated widely in China, the United States, and Central Asia. The cotton stalk generated with cotton cultivation is an important source of lignocellulosic biomass. In recent years, cotton stalk has received increasing attention from researchers engaged in bioconversion areas, and some high-value products, such as bioethanol, biogas, single cell protein1–4 have been manufactured from cotton stalk. Exploring more high-value products from bioconversion of cotton stalk may realize today’s goal of utilization of lignocellulosic biomass. Xylitol is a five-carbon sugar polyol, which is widely applied in the food, pharmaceutical and dental industries, as it has multiple properties, such as sweetness with low caloric content, anticariogeni city, tooth rehardening and remineralization, prevention of otitis.5,6 Xylitol can be produced chemically by catalytic hydrogenation of D-xylose from hemicellulosic hydrolysates or be produced by some xylose-utilizing microorganisms as a natural metabolic intermediate.7 Microbial xylitol production is more favorable for industrial applications due to mild fermentative conditions like atmospheric pressure and ambient temperature. Many yeasts, including Candida tropicalis, Debaryomyces hansenii, Candida guilliermondii, Candida subtropicalis species8–11 can effectively convert xylose into xylitol. Recently, considerable attention has been drawn to the bioconversion of xylose into xylitol from lignocellulosic hydrolysate.12,13 However, due to the inhibitors in hydrolysate, it is difficult to obtain a high xylitol concentration in the fermentation broth, so some measures like decolorization, detoxification have been introduced to deal with the inhibitors in hydrolysate. Moreover, other measures like immobilization of inoculum cells, optimization of fermentative conditions are also needed to improve xylitol production.14–17 On the whole, the growing demand for health care and food industry has led to increased efforts to optimize the fermentative conditions of xylitol production.18,19 However, few works have dealt with xylitol production from cotton stalk hydrolysate. In previous works, our lab had converted cotton stalk hydrolysate into bioethanol via microbial fermentation,20 but that was just one method of realizing bioconversion of cotton stalk. xylitol production, as well as the study on optimization of fermentative conditions, may pave a new way for bio conversion of cotton stalk hydrolysate, which Enhanced Xylitol Production from Statistically Optimized Fermentation of Cotton Stalk Hydrolysate by Immobilized Candida tropicalis