Effect of kLa and Fed-batch Strategies for Enhanced Production of Xylitol by Debaryomyces nepalensis NCYC 3413

Aims: To evaluate the effect of volumetric oxygen transfer coefficient on the production of xylitol by Debaryomyces nepalensis and to enhance the yield and productivity of xylitol by fed-batch fermentation using xylose as substrate.

Place and Duration of Study: All experiments were performed at the Applied and Industrial Microbiology Laboratory, Indian Institute of Technology Madras, from March 2013 to May 2014.

Methodology: Batch cultivations were carried out in a 7.5 L fermentor under various oxygen transfer coefficients in the range 12 to 39.6 h-1 in order to understand the effect of oxygen on xylitol production. Fed-batch studies were performed in 2.5 L bioreactor with a working volume of 1 L. The cultures were initially grown as batch cultures. Feed containing xylose and nitrogen source was added to the medium intermittently.

Samples were periodically collected at regular intervals of time and the concentrations of xylose, xylitol and glycerol were determined by HPLC.

Results: Maximal xylitol yield (0.64 g/g) and productivity (0.43 g/L·h) were obtained at kLa 13.68 h-1. The effect of pH was also studied at this kLa. A pH value of 6.0 was found to be favorable for xylitol accumulation. Fed-batch fermentation involving feeding of xylose and nitrogen source was used for xylitol production by D. nepalensis. Within the fed-batch phase, the yield of xylitol was 0.83 g/g and the productivity was increased to 0.83 g/L.h with a final product concentration of 90 g/L.

Conclusion: Higher kLa favors biomass production whereas product formation was favored at lower kLa. Fed-batch process resulted in enhancement of final product concentration by 73%.