Evaluation of activated vegetal charcoal and vegetal polymer on the detoxification of the sugarcane hemicellulosic hydrolysate for biotechnological production of xylitol / Avaliação do carvão vegetal ativado e polímero vegetal na destoxificação do hidrolisado hemicelulósico de bagaço de cana-de-açúcar para a produção biotecnológica de xilitol

Luciana Cristina Silveira Chaud

The increasing search for ethanol fuel in order to reduce the dependence and to promote the substitution of fossil fuels will contribute to higher accumulation of sugarcane bagasse in the environment. This biomass that in Brazil is a by-product of the sugar-alcohol mills, although it has been used for the generation of energy in the sugar and alcohol production, can also be used as alternative for obtainment of xylitol, contributing to bring economical advantages for sugar-alcohol mills. In this sense, researches has been performed for the biotechnological use of sugarcane bagasse for the production of xylitol, a polyol with peculiar characteristics like its sweetener power similar to that of saccharose, non-cariogenic and indicated for diabetics and obese people, as well in the treatment of respiratory diseases and in the osteoporosis prevention. Its commercial production occurs by chemical catalysis of the xylose from the rich-xylan lignocellulosic materials, which has high cost. For the biotechnological xylitol production from these materials, initially the polymeric matrix deconstruction is necessary for separation of their main fractions: the cellulose, hemicellulose and lignin. In the case of xylitol, the fraction of interest is the hemicellulose due to be constituted mainly of pentose xylose, substrate for this bioprocess. The diluted acid hydrolysis has been commonly used in the researches for the obtainment of rich-xylose hemicellulosic hydrolysates. However, in this bioprocess there is also the release/formation of toxic compounds to the microorganisms, inhibitors of enzymatic activities like phenolics, organic acids, furfural, hidroxymethilfurfural, besides metallic ions. In the present work, two detoxification methodologies for sugarcane bagasse hemicellulosic hydrolysate were used: increase of pH to 7,0 with calcium oxide, followed by the decrease to 2,5 with phosphoric acid combined with the active charcoal adsorption (1,0% w/v, 100rpm, 30min, 60°C); and vegetal polymer flocculation (15% w/v, 200rpm, 15min, 25ºC). The efficiency of these procedures was evaluated by the toxics removal analysis and the xylose-into-xylitol bioconversion using Candida guilliermondii yeast. According to the results, the pH alteration combined with the active charcoal adsorption provided higher phenolic compounds removal (80%) with consequent enhance of the fermentative parameters, yield (YP/S = 0,78g/g) and volumetric productivity (QP=0,48g/L.h) of xylitol, while vegetal polymer provide the greatest loss of ions chrome and iron (higher than 90%), beyond zinc. Evaluating the activities of the enzymes xylose reductase (XR) and xylitol dehydrogenase (XD), responsible for the initial steps of the xylose-into-xylitol bioconversion, it can be verified that there is not a correlation between their maximum activities and the condition of higher toxics removal and maximum fermentative parameters. This can be proved by the fact of the XR maximum activity (0,446 U/mgprot) was obtained in the control experiment, in which the hydrolysate was submitted only to pH adjustment for the fermentation (pH=5,5), while for XD this activity was maximum (0,565 U/mgprot) with use of vegetal polymer.

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