Significantly improved stabilization of glycoside hydrolases important in food industry by immobilization onto appropriately modified beidellite

Abstract

Three glycoside hydrolases (α-amylase, xylanase and pullulanase) were immobilized on low-cost, environmentally friendly, easily modified clay rich in beidellite. Modifications included common procedures: Na-exchange, acid activation, pillaring, pillaring followed by acid activation, and organo-modifications with chitosan. Supports were characterized by chemical analysis, low temperature N2 physisorption, X-ray powder diffraction (XRPD) and Fourier-transform infrared (FT-IR) spectroscopy. The point of zero charge was also determined. Specific activity of different immobilizates of selected glycoside hydrolases was notably influenced by the type of chemical modification of supports. For each enzyme optimal support was chosen and storage stability was tested. α-Amylase immobilized on acid-activated support retained up to 95% of its initial specific activity of 105.6 ± 5.1 U g−1 after a testing period of 120 days. The most suitable support for xylanase was chitosan-modified beidellite with having specific activity of 90.0 ± 1.4 U g−1 which retained >50% its value after 120 days. Specific activity of pullulanase immobilized on pillared sample that was subsequently activated by acid was 44.5 ± 0.7 U g−1. Initial activity was preserved up to 33% for the same testing period. Comparing these results to the storage stability of the free enzymes that completely lost their activity for the longest period of 40 days, it can be concluded that appropriately modified beidellite- based clays could be used as suitable supports for stabilization of glycoside hydrolases. Nevertheless, further characterization of immobilizates (pH, thermal and operational stability) is needed in order to raise the suitability for larger scale processes in food industry.