Encapsulation of cellulase with mesoporous silica (SBA-15)

The enzymatic activities of cellulase encapsulated onto mesoporous materials (SBA-15: Santa Barbara amorphous silica-15) of various pore size (5.4–11 nm in diameter) were studied. Cellulase is a hydrolytic enzyme which degrades cellulose into glucose. The amount of encapsulated cellulase increased with increasing pore size of SBA-15. Nevertheless, encapsulated cellulase on SBA-15 with a pore size of 8.9 nm (hereafter referred to as cel-SBA-15/8.9 nm) gave the highest enzymatic activity, despite not having the largest pore size. Generally encapsulated enzyme has a much lower activity than that of free enzyme. For example, encapsulated cellulase on amorphous silica (cel-amorphous) displays only 20% of the activity of none encapsulated cellulase (free-cel). Nevertheless, cel-SBA-15/8.9 nm retained approximately 70% of free-cel activity. This indicates that matching the cellulase molecular size and pore size of SBA-15 is an important factor for achieving high enzymatic activity of encapsulated cellulase. In order to clarify how the pore size of SBA-15 affects the encapsulation of cellulase we measured nitrogen (N2) adsorption/desorption with SBA-15 before and after encapsulation. Our results suggest that cellulase partly caps the pores of SBA-15/8.9 nm while the pores of SBA-15/11 nm were not entirely capped. Furthermore, we confirmed that the preservation stability of cel-SBA-15/8.9 nm, which had the highest activity of all Cel-SBA-15s, was improved. Thus, the enzymatic activity of encapsulated cellulase was highly retained within SBA-15, which has a pore size slightly smaller than that of cellulase.