The adsorption of laccases and ferulic acid on a lignin substrate has been studied using a quartz crystal microbalance with dissipation (QCM-D) and an atomic force microscope (AFM). Two different additional strategies were applied: ferulic acid was added after laccase pretreatment, or coadsorbed together with laccase. The effect of two laccases isolated from Trametes hirsuta and Melanocarpus albomyces was compared on lignin activation. The QCM-D results were also compared against bulk experiments on chemithermomechanical pulp. The two laccases affected the adsorption of ferulic acid differently. Adsorption of T. hirsuta laccase was not observed, while the adsorption of M. albomyces laccase was obvious. However, both laccases still activated lignin and the amount of ferulic acid adsorbed was significantly higher on laccase-activated lignin than on the non-activated one. Rinsing after activation removed some slightly bound laccase from the substrate and decreased the adsorbed amount of subsequently added ferulic acid. Interestingly, only T. hirsuta laccase could catalyse the lasting attachment of polymerised ferulic acid onto lignin. The QCM-D and AFM results correlated with the findings of studies concerning bonding of ferulic acid on chemithermomechanical pulp. Thus, this approach is useful in studying the behaviour of enzymes on lignin substrates.
- enzymatic activation
- ferulic acid