Simulação da produção de xilitol por via fermentativa a partir do hidrolisado hemicelulósico de bagaço de cana-de-açúcar utilizando o software livre Scilab

Abstract

Xylitol is a five-carbon polyalcohol presented in many fruits and vegetables, as well as yeasts, lichens and mushrooms. It is a white crystalline powder and odorless sweetener. Compared to sucrose, it has similar sweetness and reduced caloric value, besides being independent of insulin for its metabolizing, so it is tolerated by diabetics. Xylitol can be obtained by solid-liquid extraction, chemical reduction of xylose and biotechnological conversion of xylose. The low concentration of naturally occurring xylitol (less than 0.9 g/100 g) makes solid-liquid extraction process economically impracticable. The catalytic reduction of xylose offers high yields, but suffers disadvantages mainly due to extensive intermediate purification steps and huge energy requirements, which makes the overall process very expensive. The disadvantages in the conventional method of xylitol production and the market growth over the last years have motivated researches looking for alternative ways of obtaining this product. One of the most attractive processes is microbiological route, which uses microorganisms (yeasts, bacteria and filamentous fungi) with capacity to assimilate and ferment xylose. Xylose is obtained by treating methods of lignocellulosic materials, such as hydrolysis. Sugarcane bagasse is a highly lignocellulosic residue produced in Brazil as a result of the intense sugar-alcoholic activity and it can be used in xylitol production. Thus, this study aimed to simulate and evaluate batch production of xylitol by fermentation using Scilab, a free software for numerical computation. This was possible by defining kinetics for substrate consumption (xylose), cell growth (yeast) and product accumulation (xylitol) and by resolution of the ordinary differential equations resulting system. The kinetic model used was proposed by Mohamad et al. (2016) in the study of xylitol production by fermentation of pure xylose by Candida tropicalis and was suitable to this process. The simulation of data obtained by Arruda (2011) in the fermentation of detoxified hemicellulosic hydrolysate of sugarcane bagasse by Candida guilliermondii resulted in many divergences between experimental values and those predicted by the mathematical model. The kinetic model was suitable only at the beginning of the fermentation process, but it is promising in the prediction of xylitol formation from hemicellulosic hydrolysate of sugarcane bagasse. Studies indicate that this process is a satisfactory alternative for xylitol obtaining, but still needs a better understanding.