Mechanism of iron ions sorption by chitosan-genipin films in acidic media.

Chitosan-genipin (Ch-Ge) films have been proposed as wine preservative due to their capacity to uptake iron ions. The wine is an aqueous acidic solution of water and ethanol, whose acidity derives from tartaric acid. This acid has been shown to form negatively charged iron-tartrate complexes able to interact with the positively charged amine groups of chitosan, removing the iron ions from solutions. Nevertheless, it is possible that these films can uptake iron ions in the presence of other carboxylic acids. To understand the iron-binding capacity of Ch-Ge films, aqueous solutions of different carboxylic acids were prepared in the presence of iron ions and Ch-Ge films. It was observed that the Ch-Ge films only presented sorption capacity at pH 3.5 in the presence of α-hydroxypolycarboxylic acids, through electrostatic interactions. These results allow proposing a broad application of Ch-Ge films to beverages and other liquids containing malic, tartaric or citric acids.