Bioconversion of starch to Cyclodextrin using Cyclodextrin glycosyltransferase immobilized on metal organic framework

Abstract

The superiority of a metal organic framework, namely, MIL-101 (Cr) over conventional support, zeolite Y, as immobilization support for Cyclodextrin glycosyltransferase (CGTase) was investigated. The adsorption capacity, stability, and secondary structures of CGTase upon immobilization were investigated. CGTase adsorption on MIL-101 and zeolite Y was best represented by the Langmuir isotherm with optimum adsorption capacities of 37.5 and 6.1 mg/g on two supports, respectively. The deconvolution of the amide I band of the FTIR spectrum indicated that free CGTase molecules predominantly contain β-sheets, which increased with the immobilization on MIL-101 and zeolite Y from 56% to 84.1% and 69.7%, respectively, suggesting the existence of CGTase agglomerates on the supports. The CGTase immobilized on MIL-101 showed relative activity of about 50% at a substrate concentration of up to 4 g/L (compared with free enzymes) and above 3 times higher selectivity towards the more valuable α-CD. A diffusion–reaction model was used to predict the behavior of the immobilized system, and reusability studies revealed that immobilized CGTase may be utilized for numerous reaction cycles, with possible improvements via covalent attachment using glutaraldehyde. Overall, the obtained results in this study provide insights into the usefulness of MIL-101 as a suitable support for CGTase.