Infusion of essential oils for food stabilization: Unraveling the role of nanoemulsion-based delivery systems on mass transfer and antimicrobial activity

Solid food preservation with essential oils requires the use of suitable carriers, such as nanoemulsions, which are able not only to promote dispersion in the aqueous part of foods, but also to enhance mass transfer within the food matrix. The impact of emulsion formulation and mean droplet size on the rate of infusion of carvacrol in food matrices was investigated through: (a) image analysis of micrographs of histological sections of zucchini cylinders upon infusion with different emulsions stained with fluorescent dyes, and (b) microbiological assays in zucchini as well as in cooked meat sausages. The simplified geometry enabled the derivation of the effective diffusivities of the different emulsions in the food structure and their correlation with microbial inactivation. Results showed that emulsions of nanometric droplet size, below the characteristic size of inter- and intra-cellular interstices, exhibited a significantly enhanced effective diffusivity, which promoted a more efficient antimicrobial action of carvacrol. Industrial relevance The growing interest towards "greener" food products, where safety is ensured without the use of synthetic additives, has stimulated the study of essential oils as antimicrobial compounds. However, in order to overcome the limitations related to their lipophilic nature, the use of essential oils requires their encapsulation in a suitable carrier. The objective of this study is to investigate the fundamental aspects of the use of nanoemulsion-based delivery systems for essential oils, and in particular the impact of their composition and morphological characteristics on the mass transfer in solid food products, in order to enable their rational application at the industrial scale in a wide range of vegetable and animal products.