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RESEARCH PRODUCT

Influence of solvent-free reticulation treatment on edible film properties based on chitosan and gelatin, containing or not natural antioxidants : physicochemical characterisations and application

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This thesis aims to develop an edible packaging made of a mixture of chitosan and gelatin (beef or fish), to better understand the influence of the electron beam irradiation and of the incorporation of natural antioxidants on the physico-chemical and functional properties of the films. A study of the effect of irradiation on antioxidants release kinetics in a simple liquid medium was studied for validation. A preliminary study first showed that the densification of the film-forming solution and the gel during drying does not depend on the thickness or concentration or time and suggests a Fickian diffusion of water in the matrix. The permeability to water vapor increases linearly with film thickness and especially when the extent of the relative humidity differential is high. This phenomenon is attributed to a swelling mechanism and plasticization of the gelatin-chitosan network by the water. The effect of the chitosan-gelatin ratio showed an improvement of the mechanical properties and barrier to water and oxygen of the films compared to chitosan films. These performance gains are due to the good miscibility of the two macromolecules and to the molecular interactions established after the formation of a polyelectrolyte complex, as confirmed by FTIR analysis. Irradiation of films after drying increases the polarity of the surface and the film hydrophilicity, and thus induces an increase in barrier properties to water vapor and oxygen, and also of the mechanical and thermal films. However, irradiation does not change the crystallinity of the films. The incorporation of antioxidants (ferulic acid, coumarin, quercetin and tyrosol) with or without irradiation acts differently on the organization of the macromolecular network and thus on the film properties. Thus, ferulic acid and tyrosol reduce the permeability of water vapor measured in a gradient of 0-30% relative humidity, while it increases up to 90 times with a gradient 30-84 % and an irradiation treatment. The oxygen permeability decreases significantly after addition of quercetin or tyrosol and after irradiation. Ferulic acid and coumarin increases the tensile strength of the films while they are quercetin and ferulic acid which allow to increase the thermal resistance of the films. These results thus demonstrate the complexity of the interactions involved between antioxidants and the chains of chitosan and/or gelatin, their dependence on the moisture level of the system and on the impact of cross-linking treatment by irradiation. It is noticed that the irradiation has protected the active molecules against oxidation for a long period of storage of the films. Release in aqueous medium of ferulic acid is the more delayed with the highest retention in the film at equilibrium (27%). The antioxidants diffusion coefficients, determined from the release kinetics, could be modulated (about 50%) by the irradiation treatments.