Immobilized Candida tropicalis cells in freeze dried calcium alginate beads were used for production of xylitol from lignocellulosic waste like corn cob hydrolysate without any detoxification and sterilization of media. Media components for xylitol fermentation were screened by statistical methods. Urea, KH2PO4 and initial pH were identified as significant variables by Plackett-Burman (PB) design. Significant medium components were optimized by response surface methodology (RSM). Predicted xylitol yield by RSM model and experimental yield was 0.87 and 0.79 g/g, respectively. Optimized conditions (urea 1.5 g/L, KH2PO4 1.9 g/L, xylose 55 g/L, pH 6.7) enhanced xylitol yield by 32% and xylose consumption by twofold over those of basal media. In addition, the immobilized cells were reused five times at shake flask level with optimized medium without affecting the xylitol productivity and yield. Xylitol production was successfully scaled up to 7.5 L stirred tank reactor using optimized media. Thus, the optimized condition with non-detoxified pentose hydrolysate from corn cob lignocellulosic waste with minimal nutrients without any sterilization opens up the scope for commercialization of the process.
Keywords: Cell immobilization; Lignocellulose; Non-detoxified; Non-sterile; Optimization; Xylitol.