Parasuraman Selvam

We report the adsorption equilibrium, kinetics and thermodynamic studies of endo-1,4-β-D-xylanase adsorption onto ordered mesoporous matrices of silica, carbon, and zirconia. Rapid adsorption of the enzyme was observed within 5 min, and the equilibrium was attained in 60 min. The adsorption profiles were fitted to a pseudo-second-order kinetic equation indicating a tendency towards chemisorption and that the kinetics improved with temperature. Besides, it was found that the adsorption equilibrium data followed a typical Langmuir model and that the activation energy was determined using the Arrhenius equation. Likewise, the computed thermodynamic parameters revealed that the adsorption is favourable, spontaneous, and endothermic.

Nanoscale materials of carbon, silica and zirconia were used to immobilize a recombinant endo-1, 4-β-D-xylanase (XynC) of B. subtilis KCX006. The adsorption of endo-1, 4-β-D-xylanase on nanomaterials of carbon, silica and zirconia followed the pseudo-second-order kinetic model. The activation energies for adsorption of endoxylanase on carbon, silica and zirconia nanomaterials were 9.94 kJ mol−1, 40.44 kJ mol−1 and 16.33 kJ mol−1 respectively. The recovered activity (RA) of endoxylanase immobilized on carbon, silica and zirconia nanomaterials was in the range of 52%–92%. The endoxylanase immobilized on zirconia nanoparticles showed maximum RA. All immobilized endoxylanase showed optimum activity at pH 6.6 similar to that of free/soluble endoxylanase. But compared to free endoxylanase, all immobilized endoxylanase had broad optimum temperature range (50–65 °C) for catalytic activity. The Michaelis-Menten constant (Km) increased for all immobilized endoxylanase due to substrate diffusion limit. The endoxylanase immobilized on above nanomaterials was used repeatedly for XOS production from xylan. All immobilized endoxylanase produced X2–X6 and substituted XOS similar to free endoxylanase from beechwood xylan and extracted crude xylans from sorghum and sugarcane bagasse. The endoxylanase immobilized on above nanoparticles did not lose activity after five batches of repeated use. The results showed that endoxylanase immobilized on carbon, silica and zirconia matrices would be useful for production of XOS by enzyme recycling.

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-β-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°C) for optimal catalytic activity when compared with the free-XynC. Immobilization of XynC resulted in higher Km 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.