Abstract
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► Tyrosol was converted to its dimer in aqueous solution by Trametes trogii laccases. ► Tyrosl dimer showed high bactericidal and fungicidal effect of concentrations ranged between 1–0.5gL−1 and 8–4gL−1. ► Tyrosol dimer showed high insecticidal activity against Tuta absoluta, a serious pest of tomato in the world, at a concentration of 16.5gL−1. ► Laccase treatment of tyrosol allowed the removing of tyrosol phytotoxicity.
Oxidative transformation of tyrosol catalysed by Trametes trogii laccases in aqueous solution was investigated. LC–MS analysis shows that tyrosol was converted to its dimer. The enzymatic reaction was also investigated by 1H and 13C nuclear magnetic resonance, and the product formed was identified as a dimeric tetracyclic ketone. The bactericidal and fungicidal properties of tyrosol dimer were investigated using the NCCLS broth dilution and EN 1276 standard methods. High bactericidal and fungicidal effect of concentrations ranged between 1–0.5gL−1 and 8–4gL−1 were obtained. Dimer concentrations of 33gL−1 and 66gL−1 allowed reductions in viability higher than 5log units per mL for Pseudomonas aeruginosa ATCC 15442, Escherichia coli ATCC 10536 and Enterococcus hirae ATCC 10541, Staphylococcus aureus ATCC 9144 respectively, within a contact time of 5min under dirty conditions. The effect of this product on Tuta absoluta, a harmful pest of tomato in the world, was also evaluated. The results showed high insecticidal activity against this insect at a concentration of 16.5gL−1. Germinability experiments on Lycopersicum esculetum were conducted in order to evaluate the potential of a laccase treatment in removing tyrosol phytotoxicity. The results showed that tyrosol dimer was nonphytotoxic. This study presents the first comprehensive results of biological characterisation of the product obtained by the action of laccase on tyrosol transformation with T. trogii laccases.