Abstract

Xylose reductase (XR) is a key enzyme in order to obtain xylitol from xylose. It has vast applications in biotechnology including xylitol production. The present study aimed to estimate and characterize XR from Candida tropicalis strain LY15. C. tropicalis strain LY15 showed xylose utilization ability and xylose reductase activity after 48 h of incubation at pH 6.5, incubation temperature 28°C and rotation speed 140 rpm. It was specific to nicotinamide adenine dinucleotide phosphate-oxidase (NADPH) with an activity of 32.13 IU/ml. Response surface methodology (RSM) was taken into account in order to determine the effect of four main factors, that is, inoculum (1%), hemicellulose waste substrates (HWs) (2%), incubation period (60 h), and RPM (140) on enzyme production. The maximum XR enzyme activity on corn cob substrates (62.80 IU/ml) was found. The xylitol yield (12.08 g/L) attained corn cob media after 60 h of fermentation. Three dimensional response and interaction plot of the quadratic model showed interdependent interaction between the effective variables. Analysis of variance (ANOVA) predicts R2 value close to 1 which makes the result highly significant (p≤0.0001). These values were higher when compared with the traditional fermentation processes.

Key words: Candida tropicalis, corn cob, xylitol, response surface methodology (RSM), xylose reductase.