Polyethyleneimine (PEI) functionalized ceramic monoliths as enzyme carriers: Preparation and performance

Classical cordierite monoliths and acicular mullite (ACM) monoliths were used as support material for ionic adsorption of β-galactosidase from Aspergillus oryzae. Monoliths were silica-coated, then functionalized with polyethyleneimine (PEI) using different methods. In addition to direct adsorption of PEI, monoliths were modified with (3-glycidoxypropyl)trimethoxysilane (GPTMS) and γ-(aminopropyl)triethoxysilane (APTES)–glutaraldehyde for covalent attachment of the polymer. The optimal method, in terms of immobilization capacity and stability, was selected by using a particulate silica support and crushed monoliths. Immobilization of PEI via a GPTMS-functionalized ACM monolith yields the best enzyme carrier. At pH 7, 150 mg β-galactosidase g−1 SiO2 can be adsorbed. In general, a coating with a higher molecular mass polymer results in stronger immobilization, at a higher rate. By using whole monoliths, we find that the molecular weight of the polymer coating influences the adsorption/desorption of the enzyme. The open walls of the ACM monoliths permit significant higher loadings of high molecular weight PEI, which results in a higher enzyme-support strength and increased stability with respect to enzyme desorption. These PEI systems provide an optimal environment for the β-galactosidase, 92% of the free enzyme activity is retained after immobilization. Although adsorption was quite strong and permitted the use of the immobilized enzyme in a wide range of conditions, the enzyme could be completely desorbed after its inactivation. The monolith-carrier combination can be reused several times.