Immobilization of laccase and tyrosinase on untreated and plasma-treated cellulosic and polyamide membranes

Laccase and tyrosinase were immobilized by adsorption and covalent attachment onto microfiltration membranes made of cellulosic and polyamide material. Amine, hydroxyl and carboxylic functional groups for covalent attachment were generated by plasma polymerization of allylamine, allyl alcohol and acrylic acid using mild plasma parameters. Mass analysis of the modified membranes, surface tension and FTIR-ATR spectra were used to show the presence of stable plasma polymer on the membrane surface. It was shown that untreated and plasma treated cellulosic membranes were unsuitable for laccase and tyrosinase immobilization. Both, immobilization of laccase onto polyamide membrane modified with AlNH2 and adsorption on the untreated membrane at pH 5.2 gave satisfactory and comparable results with better operational stability in 10 consecutive batch processes for covalently bound enzyme. In the case of tyrosinase, adsorption of the enzyme on the untreated PA at pH 7.0 was as effective as covalent binding onto PA–AlNH2 (in pH 7.0). Operational stability was tested in the presence of diphenolic substrate, which exhibits strong suicide inactivation towards the enzyme. It was shown that immobilized tyrosinase seems to be exceptionally stable in the presence of diphenolic substrate.