Antimicrobial and antioxidant properties of chitosan enzymatically functionalized with flavonoids

Chitosan fibres were grafted with flavonoids using tyrosinase to produce reactive o-quinones which subsequently react with primary amino groups of the chitosan. The reaction mechanism using chemically different flavonoids (flavanols, flavonols, flavone, flavanone, isoflavone) was followed by UV/vis spectroscopy and the successful grafting was demonstrated by ATR-IR spectroscopy, pH potentiometric titration and reflectance measurements. An increase of antioxidant activity of functionalized chitosan fibres using well established methods was found depending on the type of the flavonoid used. In addition, some flavonoids increased antimicrobial activity of chitosan against Bacillus subtillis and Pseudomonas aeruginosa.