Activity and Reusability of Sol-Gel Encapsulated α-Amylase and Catalase. Performance in Flow-Through Systems

Abstract

A simple sol-gel procedure, based on the typical tetralkoxysilane-water-HCl reaction mixture, was used for the encapsulation of two enzymes of very different size in silica glasses. Optimization of the initial mixture composition, the hydrolysis time and the gelling and drying conditions led to the preparation of reusable porous biogels that preserved an interesting fraction of the native enzyme activity. Thus, the relative activities of the encapsulated enzymes, with respect to the enzymes in solution, were 20% for α-amylase and up to 57% for catalase. The lower performance of the former was probably due to the slow diffusion of the big substrate molecule (starch) within the gel. In the case of catalase, optimal results were obtained after washing the gel with a Triton X-100 solution; indeed, the surfactant treatment was indispensable to avoid a progressive blocking of the enzyme active sites during repeated uses of the same gel. Both biogels were packed in cartridges and tested during successive reaction cycles. Compared to batch experiments, the flow reactors were capable of transforming a higher substrate amount per unit time and, if appropriately regenerated, a practically constant efficiency was observed from cycle to cycle. These results open the way to envisage the use of the proposed sol-gel procedure for the preparation of different catalytic biogels with possible application in continuous high-throughput reactors.