Enhanced Production of Alkalo-tolerant NADPH Dependent Xylose Reductase from Emericella sp. XLT-11 by Statistical Modeling.

Xylitol is a natural sweetener with diverse pharmaceutical and industrial applications. Low concentration of xylitol in fruits and vegetables is not enough to fulfil its increasing market demand. Catalytic reduction of xylose to xylitol is although simpler and rapid but this is also cost intensive due to catalyst regeneration, requirement of purified substrate, by-product generation, and need of high energy. Therefore bio-production of xylitol is probably the most preferred solution at the moment. Since xylose reductase (XR) is the crucial enzyme for xylitol production, efforts were made to explore the potential of hyper XR producer Emericella sp. XLT-11, selected out of 228 microbial isolates (68 bacterial and 160 fungal). Statistical approach was followed to enhance the xylitol yield. Of total, ten factors tried using Placket Burman Design, only 5 exhibiting positive impact on xylitol production, were used for further screening through central composite design (CCD). Maximum XR activity was recorded with 3.25% xylose, 0.125% MgSO4 using 24 h old inoculum after 108 h of incubation at 32.5 °C. The enzyme activity showed 3.81 folds increase (126.08±1.53 U/mg protein) over the control (33.07 U/mg) with up to 64% xylose conversion after optimization. The notable factor that XR from Emericella sp. XLT-11 could retain up to 75% of enzyme activity, even at pH 10.0, can be exploited at a large scale after further R&D. Emericella sp. XLT-11 has emerged as one of the potential isolates for bioconversion of xylose to xylitol. Its stability at a higher pH range can be best utilized for xylitol production at commercial scale. [ABSTRACT FROM AUTHOR]