Properties of Chitosan-Genipin Films Grafted with Phenolic Compounds from Red Wine

Chitosan has been studied as a renewable biopolymer to form edible films and coatings to improve the shelf life of food products. Chemical modification of chitosan is a strategy to prepare chitosan films with enhanced properties to be used as food preservatives. Wine, particularly red wine, is a rich natural source of phenolic compounds, namely anthocyanins, proanthocyanidins, monomeric catechins, and phenolic acids. Phenolic compounds, in general, present strong antioxidant properties. The aim of this work was to develop chitosan-based films with higher antioxidant activity by grafting wine phenolic compounds. Fractions of red wine phenolic compounds, rich in phenolic acids, anthocyanins, and total phenolic compounds, were grafted to the glucosamine residues of chitosan by a radical mechanism using ammonium cerium (IV) nitrate. In order to increase the stability of the films in aqueous acidic medium, genipin, a natural compound with capacity of cross -linking chitosan, was also used in film preparation. The grafting of all phenolic compounds -rich fractions obtained from wine provided films with antioxidant activity more than 100% than those films prepared only with chitosan-genipin. Moreover, the use of genipin allowed obtaining stable films in a large range of pH. The chitosan-genipin film grafted with anthocyanins and total phenolic compounds lost less than 3% of their mass in acidic media after an exhaustive stirring during 7 days, only due to the diffusion of glycerol used as plasticiser. Therefore, these films are promising active materials to be used to improve food preservation.