Grafting of lactase-catalysed oxidation of butyl paraben and p-coumaric acid onto chitosan to improve its antioxidant and antibacterial activities

The grafting of laccase-catalysed butyl paraben (BPH) and p-coumaric acid (PCA) onto chitosan were performed using an eco-friendly procedure at 40 degrees C and with a phosphate buffer (100 mM, pH 6.5). Linear potentiometric titration, Fourier-transform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA) were used to characterise the graft ratio, and structural changes in the BPH- and PCA-chitosans: their antioxidant and antibacterial activities were then analysed. The results showed that the graft ratios of BPH-chitosan and PCA-chitosan were 8.0% and 10.2% respectively. The FTIR showed an absorption decrease in amino groups and a new band appeared at 1637 cm(-1) corresponding to C=N vibrations that were characteristic of imines due to Schiff base formation between the amino groups of chitosan and the phenolic hydroxyl of BPH or PCA. The thermal stability of chitosan derivatives was thus improved. Additionally, the antioxidant capacities of chitosan derivatives were improved, especially for the PCA-chitosan derivative (IC50 were 2.069 mg/mL and 0.349 mg/mL for DPPH.(+) and ABTS.(+) scavenging, respectively): the samples also exhibited an increased activity against Escherichia coli, Salmonella, Bacillus subtilis and Staphylococcus aureus compared to untreated chitosan.