Abstract
This study reports an industrially applicable non-sterile xylitol fermentation process to produce xylitol from a low-cost feedstock like corn cob hydrolysate as pentose source without any detoxification. Different immobilization matrices/mediums (alginate, polyvinyl alcohol, agarose gel, polyacrylamide, gelatin, and κ-carrageenan) were studied to immobilize Candida tropicalis NCIM 3123 cells for xylitol production. Amongst this calcium alginate, immobilized cells produced maximum amount of xylitol with titer of 11.1 g/L and yield of 0.34 g/g. Hence, the process for immobilization using calcium alginate beads was optimized using a statistical method with sodium alginate (20, 30 and 40 g/L), calcium chloride (10, 20 and 30 g/L) and number of freezing–thawing cycles (2, 3 and 4) as the parameters. Using optimized conditions (calcium chloride 10 g/L, sodium alginate 20 g/L and 4 number of freezing–thawing cycles) for immobilization, xylitol production increased significantly to 41.0 g/L (4 times the initial production) with corn cob hydrolysate as sole carbon source and urea as minimal nutrient source. Reuse of immobilized biomass showed sustained xylitol production even after five cycles.Electronic supplementary materialThe online version of this article (doi:10.1007/s13205-016-0388-8) contains supplementary material, which is available to authorized users.
Highlights
The increasing demand and exorbitant cost of low calorie polyol like xylitol open up challenge for making low-cost xylitol from renewable feedstock
Second stage dealt with influence of sodium alginate concentration, calcium chloride concentration and Xylose,xylitol (g/l)
Statistical data analysis calcium chloride was observed on yield, productivity and immobilization efficiency, moderately significant interactive effect of calcium chloride and freeze thaw cycle no was observed on immobilization efficiency (80 % \ significance \ 95 %)
Summary
The increasing demand and exorbitant cost of low calorie polyol like xylitol open up challenge for making low-cost xylitol from renewable feedstock. Xylitol is beneficial for nutrition (Sreenivas-Rao et al 2006), for prevention of dental caries (Emidi 1978) and low-calorie food preparation for diabetic patients (Pepper and Olinger 1988) but these applications are limited due to high cost of xylitol produced by chemical means. Xylitol is currently manufactured by chemical hydrogenation of pure D-xylose in the presence of nickel catalyst at elevated temperature and pressure, yielding a product with a high purity ([99.5 %) and a yield of 50–60 % with respect to the initial xylose (Dieters 1975; Ojamo et al 2009). Xylitol can be produced by biological process which shows certain advantages like milder conditions of pressure, temperature, pH, agitation, cell inhibitors and lower costs of downstream processing due to the production of lower amounts of by-products
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