Investigating the physicochemical and mechanical properties of edible active films based on gelatin containing essential oils of thyme, oregano and sage

Background and objectives: To minimize the use of antibiotics, additives, and chemical preservatives , it is possible to incorporate natural antimicrobial substances into packaging. Recent studies focusing on developing and evaluating edible films have highlighted the effectiveness of essential oils like clove, cinnamon, ginger, and basil in protecting against microbial growth, preventing food spoilage (both chemical and microbial), and reducing food waste. Films containing gelatin display impressive mechanical strength, making them suitable for edible film production due to their ability to form a gel-like structure, which is attributed to the presence of certain amino acids like proline and hydroxyproline. Taking into account the plentiful availability and affordability of thyme, oregano, and sage essential oils in our country, as well as the low cost of gelatin, this particular composition of film has yet to be extensively researched and could serve as a model for widespread implementation in the food industry.
Materials and methods: In this study, we investigated the impact of various concentrations of thyme, oregano, and sage essential oils on thr properties of the resulting gelatin-based films. The study examined different concentrations of essential oil ranging from minimum 0% to highest 4% as the independent variable. The dependent variables included a range of physicochemical tests such as solubility, water permeability, thickness, opacity, and color parameters, as well as mechanical tests including elongation to breaking point, tensile strength, and Young's model. The study utilized a mixed experimental design known as simplex lattice and employed Design Expert13 software for experimental design, analysis of variance, diagram creation, and examining the interactions between variables.
Results: In this research, the highest tensile strength (12 MPa), elongation at break point (26%) and Young's modulus (80 MPa) were found in high concentrations of oregano essential oil (4%). Among the treatments, the lowest solubility was in the high concentration of oregano essential oil in the mixture (4% area) and the lowest vapor permeability was in the area of low concentration of oregano essential oil in the mixture. The difference in the amount of turbidity of the resulting films was not significant, although it was the highest in the lowest concentration of oregano essential oil. The highest amount of thickness was obtained in the concentration of oregano essential oil in the region of 4%, which was statistically significant. By increasing the concentration of essential oil thyme in the mixture, the hue angle, whiteness index and saturation decrease, and its highest amount is in the area of 4% oregano and sage. The changes of a* and b* parameters have a trend similar to color indicators, but in relation to L*, the concentration of essential oils has no effect on the changes of this parameter.
Conclusion: The results of this research showed that adding a high concentration of oregano essential oil to the gelatin film compared to thyme and sage essential oils produced films with sufficient strength that have the highest efficiency and desirable characteristics compared to thyme and sage essential oils. It has a flower and can be used as a suitable coating for food protection by delaying the oxidation of lipids, mechanical properties and favorable color changes.