Rita C.L.B. Rodrigues, Maria das Graças A. Felipe, Arnaldo M. R. Prata and Adalberto Pessoa Jr.
Departamento de Biotecnologia (DEBIQ), Escola de Engenharia de Lorena (EEL), Universidade de São Paulo (USP), 12600-970, Lorena-SP, Brazil
To produce cost-effectively xylitol on an industrial scale by fermentation, more economic nitrogen sources needed to replace peptone, and yeast extract, which are one of the most expensive ingredients of the semi-defined medium. In our work, we used the statistical approach to get the best medium nutritional need and initial cell concentration to improve xylitol production by the yeast Candida guilliermondii FTI 20037 in sugarcane bagasse hemicelulosic hydrolysate (SBHH) containing high xylose concentration (~77g/L). We described the effects of rice bran extract (RBE) as an alternative organic complex nitrogen source and the ammonium sulfate as inorganic nitrogen, using a 23 full factorial design followed by response surface methodology (RSM). The RSM suggests the maximum values for xylitol volumetric productivity (Qp) and xylitol yield (Yp/s) by using ammonium sulfate (0.5g/L), initial cell concentration (1.0g/L) and RBE (5.0g/L) in their lowest levels. The experimental value for Qp and Yp/s were 0.73gxilitol/L.h and 0.66gxilose/gcel corresponding to a theoretical conversion efficiency (Π) of 73.06% and maximum xylitol production of 40.07g/L. The rice bran is a low cost feedstock. Inclusion of RBE improved the nutritional quality of SBHH and could be a viable alternative as an organic nitrogen source for xylitol production by yeasts.
Keywords: Sugarcane bagasse hemicellulosic hydrolysate, xylitol, yeast fermentation, nitrogen source, rice bran extract.