Preparation of active edible film based on gelatin-carboxymethylcellulose (CMC) containing portulaca oleracea extract: investigation of physicochemical and antimicrobial properties

Background and Objectives: In order to reduce the use of antibiotics, additives and chemical preservatives, natural antimicrobial substances can be used in the composition of packaging. In recent years, the use of various extracts and essential oils for microbial protection, postponing food spoilage and reducing food waste have gained significant attention in the research related to the production and evaluation of edible films. Films containing gelatin and carboxymethylcellulose have good mechanical resistance, and gelatin 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 Portulaca oleracea extract in our country and the cheap price of gelatin and carboxymethylcellulose, this type of film composition can be a model for its use in the food industry.
Materials and methods: In this research, the effect of different concentrations of Portulaca oleracea extract on the properties of gelatin-carboxymethylcellulose-based edible film was investigated. The independent variable according to the statistical design includes different concentrations of Portulaca oleracea extract (0%, 0.75%, 1.5% and 3.25%) and the dependent variables include physicochemical tests (turbidity, thickness, solubility and vapor permeability), Mechanical experiments (elongation to breaking point, tensile strength and Young's modulus), antioxidant activity and antimicrobial activity were considered. Experiments with three replications were analyzed with a completely randomized design and one-way analysis of variance with SPSS26 software at a probability level of 0.05.
Results: Among the treatments, the difference in the amount of turbidity of the resulting films was not significant (p > 0.05), although it was highest at the highest extract concentration. The greatest thickness was obtained at a concentration of 1.5% Portulaca oleracea extract, which was statistically significant (p < 0.05). Among the treatments, the lowest solubility was observed at a concentration of 3.25% Portulaca oleracea extract, and the lowest vapor permeability was found at the low extract concentration in the treatments. In this research, the highest elongation at the break point (28%), tensile strength (17 MPa), and Young's modulus (134 MPa) were recorded at the concentration of 1.5% Portulaca oleracea extract. In edible film treatments, the antioxidant activity using DPPH radicals at concentrations of 1.5% and 3.25% was significant (p < 0.05). The evaluation of the antimicrobial activity of the film was conducted using the diffusion disc method. In this test, the largest diameter of inhibition at the concentration of 3.25% extract was related to Staphylococcus aureus, with an average diameter of 15.23 mm. At the same concentration, the average diameters for Pseudomonas aeruginosa and Escherichia coli were reported as 8.16 mm and 4.5 mm, respectively.
Conclusion: The results of this research showed that adding a high concentration of Portulaca oleracea extract (3.25%) to the gelatin-carboxymethylcellulose film produced films with sufficient strength, which exhibited the highest efficiency and desirable characteristics, and can delay the oxidation of lipids. The mechanical properties and favorable physicochemical changes make it a suitable coating for food protection.