High levels of weak organic acids l

High levels of weak organic acids leads to acidification of the yeast cytoplasm and that causes a depletion in the ATP pool due to an alteration of ATP by ATPases present in the plasma membrane that pumps H+ions into the cell surroundings to regulate intracellular pH [30]. Cheng et al. [22] studied the optimization of pH and acetic acid concentration in the bioconversion of hemicellulosic hydrolysate from corncobs into xylitol by Candida tropicalis. These authors evaluated various concentrations of acetic acid infermentation media and noted that concentrations around 2 g L−1 acetic acid inhibited the production of xylitol, reducing its production by about 9%. In the present study, it was observed that the concentration of acetic acid in the CABH-1 was below the inhibitory concentration cited by these authors. In turn, the presence of acetic acid below 1 g L−1 favored xylitol production by as train of C. guilliermondii, but when above 3 g L−1 it becomes an inhibitory compound [23]. Castro et al. [29] also evaluated xylitol production by a strain of C. guilliermondii and noted that the strainw as able to metabolize 62% of the acetic acid present in eucalyptus hydrolysate medium, which corresponded to a concentration of 5 g L−1 of the acid.