Physical and antimicrobial performance of edible films based on oregano essential oil and tapioca starch emulsions

The development of environmentally friendly materials based on natural and biodegradable sources, such as starch, represents an interesting alternative to attend to the environmental problems caused by excess waste from petroleum-based packaging. The use of emulsions to obtain edible films is a novel strategy to be explored to determine how formulation and constitution affect film properties. In such context, gelatinized tapioca starch (TS) and oregano essential oil (OEO) were used to produce new active edible films using casting technique and their physical and antimicrobial properties were studied. Regarding the emulsion constitution, which was obtained employing an high-speed homogenizer, exposure to ultrasound (US) and surfactant Tween 80 (T80) content, had relevant effects on micro (0.2 to 105 μm) and nanometric (63 to 212 nm) size distributions of the TS particles and the OEO droplets. Exposure to US reduced (4.8–34 μm) and stabilized microparticles but promoted nanoparticle aggregation during storage, independently of T80 addition. T80 helped to stabilize coarse emulsions showing a Sauter diameter of 21.4 μm along storage. Films from coarse emulsions containing OEO and T80 were stiffer (stress at break: 1.8 MPa), less soluble in water (≈ 35%) and yellowish than films without T80. In addition, surfactant promoted a discontinuous microstructure of the film matrix. Both films containing OEO showed a good capacity to inhibit the growth of spoilage microorganisms (≈ 2.5–4 log cycles reductions). Due to their performance as physical and antimicrobial barriers, the films can be proposed as active packaging alternatives to stabilize and release natural preservatives to promote food preservation during storage and as a tool to support environmental sustainability.