Multi response optimization for enhanced xylitol production by Debaryomyces nepalensis in bioreactor

Abstract

In this study, the optimization of different process variables-pH (4-6), aeration rate (200-550 rpm) and agitation rate (0.6-1.8 vvm) were investigated using rotating simplex method and uniform design method to enhance xylitol production from xylose by D. nepalensis in a batch stirred tank bioreactor. Maximum xylitol productivity (0.576 g L -1 h -1 ) was obtained at pH 4.0, agitation 300 rpm and aeration 1.5 vvm by rotating simplex method. Individual optimum values of pH, agitation and aeration are 4.2, 370 rpm and 1.2 vvm, respectively, for productivity, 4.3, 350 rpm and 1.0 vvm, respectively for xylitol concentration and 4.4, 360 rpm and 0.8 vvm, respectively for yield. Using generalized distance approach, the simultaneous optimal values were found to be-pH 4.3, 370 rpm and 0.9 vvm. After multi-response analysis, batch fermentation at optimal operating conditions resulted in enhanced productivity (0.76 g L -1 h -1 ), xylitol concentration (59.4 g L -1 ) and yield (0.58 g g -1 ) with an increase of 76.74 % of xylitol productivity.

A Bibliometric Study of Scientific Publications regarding Hemicellulose Valorization during the 2000–2016 Period: Identification of Alternatives and Hot Topics

“…Research works have demonstrated the great influence of the raw lignocellulosic material on the performance [231,232]. Moreover, conditions such as temperature, pH, oxygen availability and xylose concentration affect the fermentation process [233][234][235]. The presence of chemicals toxic to the microorganisms must be taken into consideration and the implementation of different detoxification processes has been analyzed [119,183].…”

Combining Xylose Reductase from Spathaspora arborariae with Xylitol Dehydrogenase from Spathaspora passalidarum to Promote Xylose Consumption and Fermentation into Xylitol by Saccharomyces cerevisiae

“…For example, the bottleneck may be a consequence of the relatively low affinity of the cloned SpXYL2.2 xylitol dehydrogenase for both NAD + and xylitol (Table 4), or the intracellular pools of reduced or oxidized and NADH/NADPH ratio of co-substrates [49,50], or even the low affinity of yeast sugar permeases for xylose transport [5,14,51]. Nevertheless, the ASY-2 strain transformed with the pPGK-SaXYL1 and pTEF-SpXYL2.2 plasmids (Table 6) showed xylitol yields (Y p/s = 0.614 g xylitol/g xylose) and volumetric productivities (Q p = 0.513 g/L/h) as good as or superior to those reported by other naturally xylose fermenting yeasts [52][53][54][55] or even engineered S. cerevisiae strains [38,49,50]. It is important to note that the maximal expected theoretical yield for the biotransformation of xylose into xylitol is 0.905-0.917 g xylitol/g xylose consumed, depending on how the cells will regenerate the NADH/NADPH consumed in the reduction of xylose, and that no carbon is used for cell growth or production of other metabolites [56].…”

Simultaneous Production of Xylitol and Ethanol from Different Hemicellulose Waste Substrates by Candida tropicalis Strain Ly15

“…Xylitol concentration were determined using the equipped with refractive index detector and Aminex HPX-87H column (Bio-Rad, Richmond, USA) with 0.01 N H 2 SO 4 as the mobile phase running at 0.6 mL/min at 45 ºC as previously described [5]. The retention time of xylitol was 11.4 min.…”

“…The natural essential sources of xylitol are vegetables and fruits such as strawberries, yellow plum, lettuce, raspberries and cauliflower. Xylitol is used for low caloric sweetener as an appropriate sugar substitute for diabetic patients [5]. In last few years, several commercial applications of xylitol have been achieved in industries like food, dental and pharmaceuticals [6].…”