Avaliação da imobilização celular de leveduras visando a obtenção biotecnológica de xilitol

Abstract

Xylitol is a sweetener that has been intensely used in the diet due to its high sweetening capacity, as well as its use in the treatment and prevention of diabetes, since its metabolism is insulin-independent. The biotechnological xylitol production can be produced through the fermentation of pentoses, such as xylose, by the action of yeasts. This process has low yield, which has been promoting the interest in the research with alternative methods to enhanced its productivity. In this sense, cellular immobilization is a technique used to stabilize the cell and consequently improve the productivity of the process. Thus, the present study evaluated the influence of cell immobilization, using coconut and cellulose fiber as supports, in the biotechnological production of xylitol. The supports used were treated with sodium hydroxide, aiming promote better immobilization efficiency. For the fermentations, the Candida tropicalis microorganism was used, which the literature reports as one of the best producers of this bioproduct. Cell immobilization was performed by adsorption, through support immersion in a rich cell medium. The experiments were performed in 125 mL Erlenmeyer flasks, using complex medium composed of xylose (50g/L), ammonium sulfate (2,0 g/L), yeast extract (3,0 g/L), calcium chloride (0,1 g/L), with agitation of 200 rpm at a temperature of 30ºC for 36 hours and with an initial cells concentrations of 1,0 g/L. According to the results, the treatment of the supports allowed a higher immobilization efficiency, since using the coconut fiber it was possible to observe 71% efficiency, while 45% was achieved in the same type of in natura support. The maximum concentration of xylitol using immobilized cells did not show great variations as a function of the supports used, however, when using treated or in natura supports it was observed that the conversion factor from substrate to product (YP/S) was 0.49 g/g, when using in natura coconut fiber and 0.72 g/g in fermentation with treated coconut fiber. In this last condition, the highest conversion efficiency was obtained (78.6%), consequently maximum volumetric productivity (QP) (0.94 g/g L). The results of this study demonstrated the potential use of cell immobilization in order to improvement the biotechnological xylitol production.