STATISTICAL OPTIMIZATION OF MEDIUM COMPOSITION AND PROCESS VARIABLES FOR XYLITOL PRODUCTION FROM RICE STRAW HEMICELLULOSE HYDROLYSATE BY DEBARYOMYCES HANSENII VAR HANSENII

Optimization of the culture medium and process variables in xylitol production was carried out using Debaryomyces hansenii var hansenii. The optimization of xylitol production using rice straw hemicelluloses hydrolysate as substrate was performed with statistical methodology based on experimental designs. The screening of nine nutrients for their influence on xylitol production was achieved using a Plackett-Burman design. MgSO4.7H2O, (NH4)2SO4, peptone and yeast extract were selected based on their positive influence on xylitol production. The selected components were optimized with Box-Behnken design using response surface methodology (RSM). The optimum level (g/L) is: MgSO4.7H2O - 1.28, (NH4)2SO4 - 4.30, peptone - 4.98 and yeast extract - 4.58. Then the influence of various process variables on the xylitol production was evaluated. The optimal levels of these variables were quantified by the central composite design using RSM, which permitted the establishment of a significant mathematical model with a co-efficient determination of R2= 0.92. The interactive effects of process variables were determined to be significant. The optimum level of process variables are: temperature (30 oC), substrate concentration (3.26 g/L), pH (7.28), agitation speed (170.4 rpm), inoculum size (3.36 ml). These conditions were validated experimentally which revealed an enhanced xylitol yield of 0.72 g/g.