In search for practical advantages from the immobilisation of an enzyme: the case of laccase

This study investigated the efficiency of four different immobilised laccase preparations in the mediator-assisted oxidation of a non-phenolic lignin model compound. To this aim, Trametes villosa laccase was either covalently bound onto Eupergit® C or activated carbon, or entrapped within copper or calcium alginate. The benchmark reaction, consisting in the side-chain oxidation of 4-methoxybenzyl alcohol (4-MBA) to 4-methoxybenzaldehyde, was taken as the criterion to compare the efficiency of the immobilised laccases, and to assess the possible advantages of their use in alternative to the native enzyme. For each laccase preparation, four mediators (including HBT, HPI, VLA and TEMPO) were comparatively investigated. Comparisons were made by using the same amount of activity (i.e. 10 U) for each laccase preparation, and showed that the native enzyme generally led to higher p-anisaldehyde yields than the immobilised laccases. The only exception was observed with Cu-alginate-laccase, which led to a 85% conversion of 4-MBA in the presence of HBT as the mediator. When testing the reusability of this immobilised system, a significant catalytic efficiency was maintained along three consecutive reaction cycles.