Influence of Medium Composition on Xylitol Bioproduction from Wheat Straw Hemicellulosic Hydrolysate

Summary

Xylose-to-xylitol batch bioconversions from wheat straw hemicellulosic hydrolysate were carried out in Erlenmeyer flasks in order to assess the influence of medium composition (hydrolysate concentration, supplementation with ammonium sulphate, calcium chloride and rice bran extract, and initial pH) on xylitol production, productivity and yield. By using the screening design and the response surface methodologies, the statistically significant variables influencing the bioconversion were selected and linear models were fitted to the experimental data. According to the results, the best conditions to perform the bioconversion consisted in using a threefold concentrated hydrolysate supplemented with ammonium sulphate (1.0 g/l) and rice bran extract (5.0 g/l), whose pH was adjusted to 6.0 prior to inoculation. Under these conditions, a xylitol production of 24.17 g/l was observed after 72 h of fermentation, resulting in a productivity of 0.34 g/l h and in a bioconversion yield of 0.49 g/g.