PRODUCTION OF XYLOSE REDUCTASE AND XYLITOL BY Candida guilliermondii USING WHEAT STRAW HYDROLYSATES

Kklaif & Et Al

doi:10.36103/ijas.v51i6.1192

Abstract

The objective of this study is to evaluate the production of Xylose reductase (XR) and Xylitol by Candida guilliermondii using wheat straw hydrolysates (WSH) supplemented with 2.0 g/l of (NH4)2SO4 and 0.1 g/l of CaCl2.2H2O as fermentation media . Wheat straw hydrolysis run at 121°C for 15 min. by diluted sulfuric acid . The fermentation process was conducted on a shaker bath (150 rpm) at 30C for 20 h in three separate flasks using different concentration of Xylose being , 30% Xylose , WSH(27.13 g/l Xylose)and WSH plus 30 g/l Xylose. The best concentration( WSH plus 30 g/l Xylose ) was chosen to run the fermentation process for XR production at different incubation temperature ( 20, 25, 30, 35, 40, 45 C, different pH values (5, 5.5, 6, 6.5 and 7) and different fermentation period (5 , 10 , 15,20 ,25 ,30 h ). The results indicated that the optimum condition for XR production was using 30%Xylose plus WSH at pH 6 over 20h incubation at 30 C. The crude extract of Xylose reductase was used to reduce Xylose into Xylitol with simultaneous oxidation of NADPH. The crude extract of XR was able to convert about 90 % 0f the Xylose to Xylitol through 24 h. incubation at 30°C.According to these findings WSH can be used as a promising source for Xylose to produce Xylose reductase enzyme by Candida guilliermondii and the crude extract could be used successfully in conversion of Xylose to Xylitol.

Highlights

Xylose reductase (XR) (EC 1.1.1.21) is one of the main enzymes for Xylitol production, it assist the reduction of D- Xylose to Xylitol with concomitant oxidation of NADPH ( 14 )
It is not available commercially despite the several studies found in the literature on the potential usage of Xylose reductase as well as there being a description of downstream procedures regarding its separation from the yeasts (6)
The yeast, as any pentose-fermenting or pentose-utilizing microorganism, has the Xylose reductase in the cytoplasm, which catalyses the conversion of Xylose into Xylitol(2)

Summary

INTRODUCTION

Xylose reductase (XR) (EC 1.1.1.21) is one of the main enzymes for Xylitol production, it assist the reduction of D- Xylose to Xylitol with concomitant oxidation of NADPH ( 14 ). The enzyme must be obtained by cultivating the yeast Candida guilliermondii, which is reported to be one of the most efficient Xylitol producers (9) through an aerated batch process, (16). The aim of this study was to evaluate the production of Xylose reductase and Xylitol through microbial processes using the yeast Candida guilliermondii and hemicelluloses hydrolysates from wheat straw. Fermentation conditions: The fermentation process was carried out at three separate flasks , each one contained the fermentation medium that has been described in inoculums preparation section with some modification being (30%Xylose in first flask, WSH in the second one and 30%Xylose + WSH) All these medium were inoculated with 6 × 106 viable cells/ml. Statistical analysis: Data analysis for statistical significance was conducted by oneway analysis of variance (ANOVA) at a significance level of 95%

RESULTS AND DISCUSSION

Hemicelluloses Lignin

Effect of temperature on Xylose reductase production

Effect of fermentation duration on Xylose reductase production