Statistical approach to study the interactive effects of process parameters for enhanced xylitol production by Candida tropicalis and its potential for the synthesis of xylitol monoesters.

Previous results showed that an indigenously isolated yeast strain of Candida tropicalis was found to produce 12.11 g/L of xylitol under unoptimized conditions in presence of 50 g/L of xylose. In the present study, optimizing the process using one-variable at-a-time resulted in the production of 59.07 g/L of xylitol in 96 h in presence of 100 g/L xylose. Further optimization using response surface methodology led to the production of 65.45 g/L in medium containing 100 g/L xylose, 0.5% yeast extract, 0.03% MgSO(4).7H(2)O and 0.2% KH(2)PO(4), pH-4.5, 30 °C, 200 r/min for 96  h with 4% inoculum level. Addition of 1% methanol in response surface methodology optimized-medium led to the production of 67.12 g/L. Scaling up in 10 L fermentor resulted in productivity of 0.80 g/Lh with yield of 0.68 g/g. Efficient synthesis of xylitol esters was achieved with butyric acid (50.32%) and caproic acid (38.36%) in 4 h using Pseudomonas aeruginosa lipase in t-butanol: tetrahydrofuran (1:1 v/v).