Development and characterization of wheat gluten-based antibacterial/antioxidant films activated by free and encapsulated Origanum majorana L. essential oil

This research aimed to prepare wheat gluten-based films activated by free and encapsulated L. majorana Origanum essential oil (MEO). Tween 80 and whey protein isolate were utilized to prepare MEO-loaded nanoemulsion (NE) and Pickering emulsion (PE), respectively. PE and NE had particle sizes of 186.7 nm and 149.5 nm, respectively. The NE had lower zeta potential and higher encapsulation efficiency. After incorporation of the obtained nanocapsules and free MEO into the gluten films at three levels (1, 3 and 5 wt%), the morphological, physical, antioxidant and antibacterial characteristics of the active films were assessed. According to the FE-SEM analysis, the surface roughness of films increased by adding free MEO and nanocapsules. XRD test revealed that the free MEO causes a decrease in the crystallinity of the film, but its encapsulated forms had no adverse effect. Improving the thermal properties of gluten films after the incorporation of PE-MEO nanocarriers was approved by TGA analysis. Adding free and encapsulated MEO led to an increase in the water solubility of films and a decrease in the WVP. The weakening effect of MEO on the mechanical characteristics of gluten films was the lowest when the PE nanocapsules were incorporated. The antioxidant activity of the films increased significantly (p < 0.05) with the addition of free and encapsulated MEO. However, the encapsulation slightly decreased the antibacterial potential of MEO against E. coli and S. aureus. To conclude, the produced active gluten film with encapsulated MEO, especially the PE one, presented considerable potential for use as active food packaging.