Effect of natural polymer emulsifiers on the release behavior and blueberry preservation performance of chitosan–thyme essential oil composite films

Abstract Currently, research on how different natural polymer emulsifiers systematically affect the physical properties, structure, essential oil release behavior, and blueberry preservation efficacy of chitosan-based essential oil composite films remains insufficient. To investigate this, the present study selected gum arabic, gelatin, methyl cellulose, and tragacanth gum as polymer emulsifiers to prepare chitosan-based thyme essential oil composite films [these four treatments were designated as CA (film with gum arabic), CG (film with gelatin), CM (film with methyl cellulose), and CT (film with tragacanth gum), respectively, while the film without an emulsifier was designed as CS]. The results indicated that incorporating emulsifiers changed the physical properties of the composite films, in particular reducing water content and mechanical strength but significantly improving antioxidant activity and antimicrobial activity as well as their ability to retain freshness. The film with added methyl cellulose exhibited the strongest antioxidant activity, twice that of the CS film, while the activity of the CA, CG, and CT films was approximately 1.6 times that of the CS film. Adding emulsifiers significantly inhibited the growth of gray mold, with the antibacterial effects of CM and CG being markedly superior to those of the other treatment groups. Thermal properties showed that the addition of emulsifiers reduced the thermal stability of the composite films, and the interactions between the CM and CG films were stronger than those between the CA and CT films. Fourier transform infrared spectroscopy and scanning electron microscopy revealed that the emulsifier decreased the surface roughness of the chitosan film, indicating a strong interaction between the two. The physical properties of the film, the release of essential oils, and the antimicrobial activity are all influenced by the type of emulsifier used, the choice of solvent, and the interactions between the emulsifier and the film matrix. Additionally, the antimicrobial chitosan composite film packaging significantly improved the freshness preservation of blueberries, better preserving fruit's color, flavor, and freshness. A chitosan-based composite film containing methyl cellulose may be the best choice for producing active composite films, as it exhibits stronger antioxidant and antimicrobial activity than the control film.