Immobilization of Recombinant Endo-1,4-β-xylanase on Ordered Mesoporous Matrices for Xylooligosaccharides Production

Xylooligosaccharides (XOS) are emerging prebiotics, widely used in food, medicine and health care. XOS are produced by hydrolysis of xylan by acid or endoxylanase enzyme. Xylanase hydrolysis is preferred over acid due to its high specificity and absence of formation of non-toxic byproducts. Immobilized xylanase improves enzyme-stability and efficacy of XOS production through its repeated use. Though there are a few xylanases immobilized on conventional organic polymers for XOS production, immobilization of xylanse on mesoporous inorganic materials have not been investigated for XOS production. In this study, the recombinant endo-1, 4-beta-D-xylanase (XynC) of B.subtilis KCX006 was purified and immobilized on ordered mesoporous matrices of carbon (CMK-3), silica (SBA-15) and zirconia (ZMF-127). The immobilized-XynC was characterized and used for XOS production by recycling. The recovered activity (RA) of immobilized-XynC varied between 55 to 84%. The maximum RA was observed for XynC immobilized on ZMF-127 matrix. All immobilized-XynC had optimum pH similar to that of free-XynC. But all immobilized-XynC gained broader temperature range (50-65 degrees C) for optimal catalytic activity when compared with the free-XynC. Immobilization of XynC resulted in higher K-m due to substrate diffusion limit. All immobilized-XynC produced free-XOS of DP 2-6 (X2-X6) and substituted-XOS from beechwood xylan and extracted crude xylans from sorghum stalks and sugarcane bagasse (SCB). The XynC immobilized on SBA-15 produced higher proportions of X2-X6 compared to ZMF-127 and CMK-3. The XynC immobilized on SBA-15 and CMK-3 retained higher activity of 85-93% after four batches of repeated use. The observed efficiency of XynC immobilized on CMK-3 and SBA-15 are higher than the reported values. The results showed that XynC immobilized on mesoporous carbon and silica matrices would be useful for production of XOS by enzyme recycling.