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

Abstract

The inhibitory action of acetic acid, ferulic acid, and syringaldehyde on metabolism of Candida guilliermondii yeast during xylose to xylitol bioconversion was evaluated. Assays were performed in buffered and nonbuffered semidefined medium containing xylose as main sugar (80.0 g/l), supplemented or not with acetic acid (0.8-2.6 g/l), ferulic acid (0.2-0.6 g/l), and/or syringaldehyde (0.3-0.8 g/l), according to a 2(3) full factorial design. Since only individual effects of the variables were observed, assays were performed in a next step in semidefined medium containing different concentrations of each toxic compound individually, for better understanding of their maximum concentration that can be present in the fermentation medium without affecting yeast metabolism. It was concluded that acetic acid, ferulic acid, and syringaldehyde are compounds that may affect Candida guilliermondii metabolism (mainly cell growth) during bioconversion of xylose to xylitol. Such results are of interest and reveal that complete removal of toxic compounds from the fermentation medium is not necessary to obtain efficient conversion of xylose to xylitol by Candida guilliermondii. Fermentation in buffered medium was also considered as an alternative to overcome the inhibition caused by these toxic compounds, mainly by acetic acid.

Biological activities of lignin hydrolysate-related compounds

“…3), and it inhibits cellulose hydrolysis in wet cake by endo-and exo-cellulases, and cellobiose hydrolysis by beta-glucosidase (77). The inhibitory effect of on metabolism of Candida guilliermondii yeast during xylose to xylitol bioconversion was evaluated and concluded that syringaldehyde may affect cell growth and metabolism of this organism (78). Furthermore, the inhibitory effects of syringaldehyde on a fermentation by Saccharomyces cerevisiae K35 was investigated and it was found that concentrations higher than 5 g/L of syringaldehyde were toxic (79).…”

Detoxification of Corncob Acid Hydrolysate with SAA Pretreatment and Xylitol Production by ImmobilizedCandida tropicalis

“…Furfural, the dehydration product of pentoses, was commonly found in hemicellulose hydrolysis [6]. Pereira et al [7] reported that the inhibitors of acetic acid, ferulic acid, and syringaldehyde in fermentation substrate would affect microbial cell growth, xylose consumption, and xylitol yield during microbial fermentation for xylitol production. The toxicity of acetic acid was more severe under low pH conditions than under high pH conditions [8, 9].…”

Xylitol Biological Production: A Review of Recent Studies

“…If the employed yeast strain exhibits rather good tolerance to toxic substances, the complete removal of toxic compounds from the fermentation medium is not necessary (37) ; in fact, some toxic substances at low concentrations may even be beneficial to xylitol production. These yeasts exhibit good activity in degrading toxic substances and many small molecule impurities (acetic acid, furfural, phenol), which significantly improves xylitol fermentative production performance and effectively reduces the burden of physical and chemical purification or detoxification processes.…”