Essential oil loaded edible films prepared by continuous casting method: Effects of casting cycle and loading position on the release properties

The fast evaporation rate and burst release of essential oils during the film preparation and application jeopardize the long-term antimicrobial efficiency of essential oil loaded active films. In the present study, oregano essential oil (OEO) loaded zein/gelatin (Z/G) monolayer and multilayer films were prepared via a continuous casting method. The self-assembly behavior of zein in continuous gelatin matrix was affected by the casting cycle, where zein microspheres with different sizes distributed in different casting layers. The cross-section structure of Z/G films then affected the retention rate of OEO and the water vapor permeability. The mechanical and thermal properties were not significantly affected by increasing the casting cycle, indicating that cohesive films were obtained by continuous casting method and the prolonged drying time did not jeopardize the thermal stability. By concentrating the position of OEO loaded layers in the intermediate and/or upper layer, films exhibited higher retention rate with preferable release properties featuring the sustained-release profile in the aqueous food simulant and the higher release rate and content in the fatty food simulant, and prolonged antimicrobial effect was observed in the preservation test on strawberries. Our work adds new knowledges to the effects of casting cycle and loading position of OEO during continuous casting process on the physicochemical properties and antimicrobial efficiency of active films.