Can Satureja montana Essential Oil Promote Edible Films Based on Plum Oil Cake into Antimicrobial and Antioxidant Food Packaging?

This study adheres to the principles of the circular economy by valorising fruit processing waste—specifically, the oil cake remaining after the cold pressing of plum seeds—for the production of new biopolymer packaging material. This study investigates the effects of incorporating Satureja montana essential oil (SMeo) on the properties of plum oil cake (POC)-based biofilms for potential food packaging applications. The mechanical, physico-chemical, barrier, structural, thermal, and biological properties of the POC-based film were investigated. The results showed that the addition of SMeo had the greatest impact on improving the water vapor barrier permeability (up to 48%). Antimicrobial analyses showed outstanding results against bacteria, yeasts, and molds, with the most pronounced inhibition observed for A. ochraceus and S. aureus. On the other hand, structural analysis confirmed that the 3% SMeo sample underwent the greatest changes, as indicated by the appearance of new bonds originating from oil–biopolymer interactions. This observation was further supported by thermal analysis, which showed that films containing SMeo degraded more rapidly than the control in a dose-dependent manner. The reduction in tensile strength values (up to 35%) suggests that SMeo-loaded POC films are more suitable for use as coatings rather than standalone packaging materials.