A comparison of lipase and trypsin encapsulated in mesoporous materials with varying pore sizes and pH conditions

Immobilized enzymes have an advantage over enzymes free in solution in that they are easily recovered after completed reaction. In addition, immobilization often gives enhanced stability. Entrapment of an enzyme in the pores of a mesoporous material is an attractive procedure since the enzyme is immobilized without any covalent bonding to a support which may be detrimental to the catalytic performance. The objective of this work is to compare the encapsulation and catalytic performance of lipase from Mucor miehei and trypsin from bovine pancreas, two hydrolases with rather dissimilar properties and structures. We also demonstrate the importance of the pore dimensions and the pH for proper function of the encapsulated enzyme. Mesoporous silica particles (SBA-15) with three different pore sizes (50 angstrom, 60 angstrom and 89 angstrom) were synthesized and hexagonal structures with narrow pore size distributions were confirmed with TEM, SAXS and N(2)-adsorption. Lipase and trypsin were encapsulated separately in the silica particles and the results indicate distinct differences between the two enzymes, both in loading capacity and catalytic activity. For trypsin the encapsulation rate and the loading capacity were large with a maximum reached at pH 7.6. The largest product yield was obtained with the particles with 60 angstrom pores, however, the yield was significantly lower than with free trypsin. For lipase optimal encapsulation rate and loading capacity were reached with the particles with 89 angstrom pores at pH 6.0 but were low compared to trypsin. However, the catalytic activity of the encapsulated lipase was more than twice as large as for free lipase, which can be explained by an interfacial activation of lipase at the silica surface