Laccase-mediated functionalization of chitosan by caffeic and gallic acids for modulating antioxidant and antimicrobial properties

► Laccase-mediated and pH dependent synthesis of phenolic acid with chitosan. ► Coupling of phenolic o-quinone with chitosan amino groups above pH 4.5. ► Ester formation through chitosan hydroxyl groups below pH 4.5. ► New bi-functionalized chitosan with modulated antimicrobial and antioxidant activity.