CotA laccase-ABTS/hydrogen peroxide system: An efficient approach to produce active and decolorized chitosan-genipin films

Chitosan-genipin films present a bluish-green color due to the conjugated double bonds formed when monomeric or dimeric genipin residues bridge chitosan. This phenomenon limits their use when colorless materials are required. In this work, a two-step oxidation strategy was developed aiming to remove color from chitosan-genipin films while preserving their functional properties. A combined system using the recombinant CotA laccase from Bacillus subtilis mediated by 2,2′-azinobis-(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) followed by a H₂O₂ oxidation step was settled. ABTS boosted the laccase performance resulting in light brown chitosan-genipin films that were further decolorized upon immersion in a 5% H₂O₂ solution at pH 11.0 and 40 °C for 30 min. The applied methodology leads to films that sustain both acidic stability and antioxidant capacity of the pristine films. Overall, the combined CotA laccase-ABTS/hydrogen peroxide developed methodology efficiently produce active and decolorized chitosan-genipin films with potential for application as eco-friendly transparent material which may have application as food packaging.