Inhibitory effect of acetic acid on bioconversion of xylose in xylitol by Candida guilliermondii in sugarcane bagasse hydrolysate

Abstract

Sugarcane bagasse hydrolysate (initial acetic acid concentration = 3.5g/L), was used as a fermentation medium for conversion of xylose into xylitol by the yeast Candida guilliermondii FTI 20037. Acetic acid (2.0g/L) was added to the medium at different times of fermentation, with the aim of evaluating its effects on the bioconversion process. The addition of acetic acid to the medium after 12h of fermentation resulted in the strongest inhibition of the yeast metabolism. In this case, the xylose consumption and cell growth were, respectively, 23.22 and 11.24% lower than when acid was added to the medium at the beginning of fermentation. As a consequence of the inhibitory effect, lower values of the xylitol yield (0.39g/g) and productivity (0.22g/L.h) were observed, corresponding to a reduction of 36 and 48%, respectively, in relation to the values obtained with the addition of acetic acid after other fermentation times. The results obtained allowed to conclude that, under the experimental conditions employed in this work, the inhibitory effect of acetic acid on the xylose-xylitol bioconversion depends on the fermentation time when this acid was added, and not only on its concentration in the medium.

Inhibitory action of toxic compounds present in lignocellulosic hydrolysates on xylose to xylitol bioconversion by Candida guilliermondii

“…The fermentation parameters values (Table 3) reveal that the effect of acetic acid was more evident on cell yield factor (Y X/S ), which decreased by 33% when the medium was supplemented with 2.6 g/l of this acid, while Q P and Y P/S were reduced by 16% and 5%, respectively. Similar behavior was reported by Silva et al [16] when evaluating the effect of acetic acid on xylose to xylitol bioconversion by C. guilliermondii from sugarcane bagasse hemicellulosic hydrolysate. According to those authors, a reduction of 17% in cell growth was observed when the fermentation medium contained 2 g/l acetic acid.…”

Production of bioalcohols and antioxidant compounds by acid hydrolysis of lignocellulosic wastes and fermentation of hydrolysates with Hansenula polymorpha

“… and Silva et al. found xylitol yields higher than in this work with H. polymorpha at the same temperature (30ºC). Similar to this work, these authors find that the presence of acetic acid in the hydrolysates caused inhibitory effects in the d ‐xylose‐xylitol conversion.…”

Xylitol production from cashew apple bagasse by Kluyveromyces marxianus CCA510

“…The most suitable detoxification process to improve fermentation of hemicellulose hydrolysates depends on its very nature; the ideal method should eliminate the greatest amount of toxic compounds and cause the lowest loss of fermentable sugars. However, to achieve an efficient fermentation, once the process parameters have been evaluated, it must be defined whether it is necessary a total or a partial reduction of the inhibitors compounds so as not to bring about a negative effect in the cellular metabolism of the yeast [31]. Some researches show the amount of inhibitors released after hydrolysis treatments.…”