Characterization of physicochemical, mechanical and antimicrobial properties of gelatin edible films containing oregano essence

In order to reduce the use of antibiotics, additives and chemical preservatives, natural antimicrobial substances can be used in the composition of packaging. In the researches related to the production and evaluation of edible films in recent years, the use of essential oils (such as clove, cinnamon, ginger and basil essential oils) for microbial protection, delay food spoilage (chemical and microbial) and reducing food waste has a significant place. Films containing gelatin have good mechanical resistance and this substance can be used in the production of edible film due to its gel-forming properties (the presence of proline and hydroxyproline amino acids). Considering the abundance and availability of oregano in our country and considering the cheap price of gelatin, this type of film composition has no research history and can be a patent for its wide use in food.

In this research, the effect of different concentrations of oregano essential oil on gelatin was investigated and the properties of the edible film were evaluated. The independent variable includes different concentrations of oregano essential oil (0%, 1.25%, 2.5% and 3.75%) and the dependent variables include physicochemical tests (solubility, vapor permeability, thickness and turbidity), mechanical tests (elongation to the breaking point, tensile strength and Young's model), antioxidant property and antimicrobial activity of edible films. All experiments were performed in three replicates (n=3) with completely random sampling. One-way analysis of variance (ANOVA) and comparison of mean data was performed based on Duncan's multi-range test using Minitab18 software at a probability level of 0.05.

In this research, the highest tensile strength and elongation at break point was 2.5% in the treatment. In the treatments of the films, the lowest solubility and permeability were observed in the concentrations of 3.75% and 1.25% of essential oil, respectively. In all treatments, turbidity was not significant, and in essential oil concentration of 2.5%, it had the highest value among the treatments. The maximum thickness of 3.75% essential oil concentration was 0.058 mm, which was not significant in all treatments (p<0.05). Antioxidant property was significant in all treatments of edible films (p<0.05). The largest diameter of the inhibition halo in the diffusion disk method in the concentration of 3.75% essential oil was related to Staphylococcus aureus with an average of 18.26 mm. The mean halo diameter for Pseudomonas aerogenesa and Escherichia coli was reported to be 8.27 and 8.9 mm, respectively.

The results of this research showed that adding oregano essential oil to gelatin film at a concentration of 2.5%, in addition to inhibiting the growth and proliferation of bacteria, created films with sufficient strength and als it can also be used in perishable foods .