Phase separation behavior in zein-gelatin composite film and its modulation effects on retention and release of multiple bioactive compounds

The zein-gelatin (ZG) composite films with customized phase separation structure were fabricated for simultaneous loading and release of tea polyphenol (TP) and oregano essential oil (OEO). The effect of phase separation behavior in ZG films on mechanical and barrier properties was investigated, and retention and release properties of TP and OEO in the selected film were evaluated. Decreasing the mass ratio of zein to gelatin, the morphology of ZG films evolved from the macroscopic phase separation with identified layer boundary (ZG(3:1), ZG(2:1)) to microscopic phase separation with spherical aggregates dispersed in a continuous matrix (ZG(1:1), ZG(1:2), ZG(1:3)). The ZG(1:2) film, characterized by microscopic phase separation structure with proper mechanical properties, low WVP and one-way moisture barrier property, was selected as an effective carrier for the simultaneous loading of TP and OEO. The Z(O)G(TP) film displayed a rough surface morphology caused by TP, and graininess cross-section morphology resulting from the OEO loaded zein aggregates. FTIR results confirmed the existence of hydrogen bond and hydrophobic interactions among TP, OEO and film matrix, respectively. The simultaneous loading led to stronger water barrier property with higher retention rate of TP and OEO in ZG(1:2) film. Kinetic analysis suggested the release mechanisms of TP and OEO from Z(O)G(TP) film were non-Fick diffusion and were close to the first-order release kinetic. The novel active film with suitable phase separation structure to load and release of multiple bioactive compounds is of particular interest for the design of multifunctional bioactive packaging with tailored structure and performance.