Xylose reductase (XR) is an intracellular enzyme, which catalyzes xylose to xylitol conversion in the microbes. It has potential biotechnological applications in the manufacture of various commercially important specialty bioproducts including xylitol. This study aimed to prepare XR from adapted strain of Candida tropicalis and to characterize it. The XR was isolated from adapted C. tropicalis, cultivated on Meranti wood sawdust hemicellulosic hydrolysate (MWSHH)-based medium, via ultrasonication, and was characterized based on enzyme activity, stability, and kinetic parameters. It was specific to NADPH with an activity of 11.16 U/mL. The enzyme was stable at pH 5-7 and temperature of 25-40 °C for 24 h and retained above 95 % of its original activity after 4 months of storage at -80 °C. The K m of XR for xylose and NADPH were 81.78 mM and 7.29 μM while the V max for them were 178.57 and 12.5 μM/min, respectively. The high V max and low K m values of XR for xylose reflect a highly productive reaction among XR and xylose. MWSHH can be a promising xylose source for XR preparation from yeast.
Kenaf (Hibiscus cannabinus L.), a potential fibre crop with a desirably high growth rate, could serve as a sustainable feedstock in the production of xylitol. In this work, the extraction of soluble products of kenaf through dilute nitric-acid hydrolysis was elucidated with respect to three parameters, namely temperature, residence time, and acid concentration. The study will assist in evaluating the performance in terms of xylose recovery. The result point out that the maximum xylose yield of 30.7 g per 100 g of dry kenaf was attained from 2% (v/v) HNO3 at 130 °C for 60 min. The detoxified hydrolysate was incorporated as the primary carbon source for subsequent fermentation by recombinant Escherichia coli and the performance of strain on five different semi-synthetic media on xylitol production were evaluated herein. Among these media, batch cultivation in a basal salt medium (BSM) afforded the highest xylitol yield of 0.35 g/g based on xylose consumption, which corresponded to 92.8% substrate utilization after 38 h. Subsequently, fermentation by E. coli in the xylose-based kenaf hydrolysate supplemented with BSM resulting in 6.8 g/L xylitol which corresponding to xylitol yield of 0.38 g/g. These findings suggested that the use of kenaf as the fermentation feedstock could be advantageous for the development of sustainable xylitol production.
Xylose-rich sawdust hydrolysate can be an economic substrate for the enzymatic production of xylitol, a specialty product. It is important to identify the process factors influencing xylitol production. This research aimed to screen the parameters significantly affecting bioxylitol synthesis from wood sawdust by xylose reductase (XR). Enzymatic bioxylitol production was conducted to estimate the effect of different variables reaction time (2-18 h), temperature (20-70 °C), pH (4.0-9.0), NADPH (1.17-5.32 g/L), and enzyme concentration (2-6 %) on the yield of xylitol. Fractional factorial design was followed to identify the key process factors. The screening design identified that time, temperature, and pH are the most significant factors influencing bioxylitol production among the variables with the values of 12 h, 35 °C, and 7.0, respectively. These conditions led to a xylitol yield of 71 % (w/w). This is the first report on the statistical screening of process variables influencing enzyme-based bioxylitol production from lignocellulosic biomass.