Novel textile dye obtained through transformation of 2-amino-3-methoxybenzoic acid by free and immobilised laccase from a Pleurotus ostreatus strain

Transformation of 2-amino-3-methoxybenzoic acid into novel and eco-friendly orange dye (N15) was performed using native and immobilised laccase (LAC) from Pleurotus ostreatus strain. A several parameters affecting lac- case-mediated transformation efficiency included the selection of type and pH value of buffer, reaction tem- perature, substrate and laccase concentration as well as the type of carrier and LAC storage conditions were evaluated. The optimal conditions for N15 dye synthesis were 40 mM sodium-tartrate buffer pH 5.5 containing 3 mM of the substrate, efficiently transformed by 2 U of free laccase per 1 mmol of the substrate. Laccase was immobilised on porous Purolite® carriers, which had never been tested as a support for oxidoreductases. Immobilised laccase, characterised by a high immobilisation yield, was obtained by adsorption of laccase on a porous acrylic carrier with octadecyl groups (C18) incubated in optimum conditions of 40 mM phosphate buffer pH 7.0 containing 1 mg of laccase per 1 g of the carrier (wet mass). The immobilised LAC showed the highest storage stability for 21 days and higher thermostability at 40 °C and 60 °C in comparison to its native form. The N15 dye showed good dyeing properties towards natural fibres, and the dyed fibre demonstrated resistance to different physicochemical factors during use, which was confirmed by commercial quality tests. The N15 dye is a phenazine, i.e. a heterogenic compound containing amino-, methoxy-, and three carboxyl functional groups with the molecular weight of approximately 449.37 U.