Functionalization of chitosan by laccase-catalyzed oxidation of ferulic acid and ethyl ferulate under heterogeneous reaction conditions

Chitosan particles were functionalized with ferulic acid (FA) and ethyl ferulate (EF) as substrates using laccase from Myceliophtora thermophyla as biocatalyst. The reactions were performed with chitosan particles under an eco-friendly procedure, in a heterogeneous system at 30°C, in phosphate buffer (50mM, pH 7.5). The FA-chitosan derivative presented an intense yellow-orange color stable while the EF-chitosan derivative was colorless. The spectroscopic analyses indicated that the reaction products bound covalently to the free amino groups of chitosan exhibiting a novel absorbance band in the UV/Vis spectra between 300 and 350nm, at C-2 region by the duplication of C-2 signal in the ¹³C NMR spectrum, via Schiff base bond (NC) exhibiting novel bands in the FT-IR spectrum at 1640 and 1620cm^-1. Additionally, antioxidant capacities of chitosan derivatives showed that the chitosan derivatives presented improved antioxidant properties, especially for FA-chitosan derivative (EC₅₀ were 0.52±0.04, 0.20±0.02mg/ml for DPPH and ABTS⁺ scavenging, respectively).