The behavior of key enzymes of xylose metabolism on the xylitol production by Candida guilliermondii grown in hemicellulosic hydrolysate

Abstract

A variety of raw materials have been used in fermentation process. This study shows the use of rice straw hemicellulosic hydrolysate, as the only source of nutrient, to produce high added-value products. In the present work, the activity of the enzymes xylose reductase (XR); xylitol dehydrogenase (XD); and glucose-6-phosphate dehydrogenase (G6PD) during cultivation of Candida guilliermondii on rice straw hemicellulosic hydrolysate was measured and correlated with xylitol production under different pH values (around 4.5 and 7.5) and initial xylose concentration (around 30 and 70 g l(-1)). Independent of the pH value and xylose concentration evaluated, the title of XD remained constant. On the other hand, the volumetric activity of G6PD increased whereas the level of XR decreased when the initial xylose concentration was increased from 30 to 70 g l(-1). The highest values of xylitol productivity (Q (P) approximately 0.40 g l(-1)) and yield factor (Y (P/S) approximately 0.60 g g(-1)) were reached at highest G6PD/XR ratio and lowest XR/XD ratio. These results suggest that NADPH concentrations influence the formation of xylitol more than the activity ratios of the enzymes XR and XD. Thus, an optimal rate between G6PD and XR must be reached in order to optimize the xylitol production.

Evaluation of hexose and pentose in pre-cultivation of Candida guilliermondii on the key enzymes for xylitol production in sugarcane hemicellulosic hydrolysate

“…The proportion of cell suspension to glass beads was 1:1 v/v. According to Gurpilhares et al (2009), the disruption period of 5 min was intercalated minute-by-minute in ice bath for 30 s. After cell disruption, the samples were centrifuged (67009g, 10 min, 4°C) and the supernatants were assayed for XR and XDH activities. Enzymes activities were determined by spectrophotometer at 340 nm, at room temperature as described by Alexander (1985).…”

Process Integration for the Disruption of Candida guilliermondii Cultivated in Rice Straw Hydrolysate and Recovery of Glucose-6-Phosphate Dehydrogenase by Aqueous Two-Phase Systems

“…Therefore, if these cells were not disposable, they could represent a potential source of important intracellular enzymes such as xylose reductase, xylitol dehydrogenase [3], and glucose-6-phosphate dehydrogenase [2]. Previously, a work was published to elucidate the behavior of key enzymes of xylose metabolism in the xylitol production by C. guilliermondii grown in hemicellulose hydrolysate and the feasibility of an integration process of xylitol production and glucose-6-phosphate dehydrogenase extraction from biomass [4].…”

Deacetylation Followed by Fractionation of Yellow Poplar Sawdust for the Production of Toxicity-Reduced Hemicellulosic Sugar for Ethanol Fermentation

“…However, these alkaline conditions to obtain lignin are not suitable at the biorefinery concept, because recovery of hemicellulosic sugar in hydrolyzate derived from alkaline-treated biomass is not easy for microbial fermentation, due to the high amount of lignin degradation compounds and others [17]. The loss of hemicellulosic sugars, mainly xylose, must be avoided, because these pentose sugars can be converted into higher value compounds, including ethanol, xylitol, and others [18,19], contributing to the economic feasibility of the biorefineries. To solve this problem, the deacetylation process at low severe condition prior to dilute acid fractionation could show not only significant improvement on sugars yields, but also toxicity reduction in hydrolyzate, thereby enhancing bioethanol production [20].…”