Probing the confinement of beta-galactosidase into meso-macro porous silica by Raman spectroscopy

Abstract

Immobilization of beta-galactosidase (beta-gal) into porous materials might afford to supported biocatalysts for the hydrolysis of diary products or to food additives for lactose intolerant people. Activity and stability of the loaded material generally depend on the interactions between the enzyme and the support, as well as on the pore size. Herein, Raman spectroscopy was used to evaluate the specific adsorption the enzyme into meso-macroporous silica materials, containing interconnected mesopores of 9 nm and macropores of 200 nm. Non-porous silica was used as reference material to determine the Raman fingerprint of physisorbed enzyme in the absence of any confinement. While the beta-gal physisorbed on the surface of non-porous silica material exhibits the same Raman spectra as the free enzyme, the enzyme physisorbed onto meso-macroporous materials show frequency displacements of characteristic amide groups as a function of initial concentration of the feed enzymatic solution. In fact, at low initial concentration in enzyme, no shifts of the amides were recorded on Raman spectra as compared with free enzyme, indicating a preferential physisorption into macropores. By increasing the enzyme concentration, the frequency of Amide I was shifted to lower values, suggesting thus a confinement into mesopores. Finally, the enzyme concentration effect can be demonstrated by the increment of the amide band intensity in the range of 1700-1500 cm(-1) as the amount of adsorbed enzyme increases. Thus, the textural properties of silica materials seem to be the key factor in the enzyme adsorption.