production of antimicrobial active edible film based on gelatin containing salvia officinalis essential oil: physical, mechanical, antioxidant and antimicrobial properties

The use of plastic packaging to cover food faces many challenges due to reasons such as non-degradation and migration of toxic chemicals such as bisphenol A, alkylphenol, octylphenol, phthalates, lead, etc. Therefore, other coatings have been focused in the food industry, which can be called edible composite films, which are considered as one of the basic ways to control the physiological, microbial and physicochemical changes of food. Films containing gelatin have good mechanical resistance and this substance can be used in the production of edible film due to its gelling properties (the presence of proline and hydroxyproline amino acids). Gelatin can form an edible layer to protect against desiccation, light and oxygen. However, gelatin films have relatively poor mechanical properties and water resistance. Adding compounds including plant essential oils is one of the ways to improve the physicochemical properties of gelatin layers to strengthen their structure. However, gelatin film has poor antimicrobial and antioxidant properties and is therefore not suitable for packaging perishable food and meat products.The use of plant essential oils in biodegradable films improves the antimicrobial, antioxidant and permeability effects of hydrophilic films. On the other hand, the combination of essential oils with films reduces the loss of volatile compounds of essential oils during storage, so the essential oil remains in a high concentration and for a longer time on the surface of the food product.In order to reduce the consumption of antibiotics, chemical additives and preservatives, natural antimicrobial substances can be used in the composition of these packages. In recent years, in research related to the production and evaluation of edible films, plant essential oils such as clove, cinnamon, ginger, and basil essential oils have received much attention for microbial protection, delaying chemical and microbial spoilage, and reducing food waste. In general, essential oils are volatile natural compounds that are secondary metabolites of GRAS-listed plants. The essential oils obtained from different plants have extensive antioxidant properties, which are related to the presence of hydrogen-containing groups in their chemical structure. Common sage (Salvia officinalis) is a perennial and herbaceous plant, with straight roots and many branches, and has the highest amount of volatile compounds, including camphor, alpha and beta thujone. Among the spices, sage is often used in pharmaceuticals as a spice that has an essential oil with good antimicrobial and antioxidant properties. The purpose of this research is to investigate the antioxidant properties of sage essential oil in the production of gelatin film with sage essential oil.In recent years, many studies have been conducted on natural preservatives. Researchers have demonstrated the use of plant essential oils to protect all types of food against spoilage and disease causing microorganisms. The name salvia is derived from the Latin word meaning to heal. This plant has received special attention since ancient times, it is the most valuable medicinal type of dark mint and has important therapeutic properties. Sage is used in traditional medicine as an effective medicine to treat the effects of insect bites, anti-poison and tonic to strengthen the soul, body and prolong life and as a tonic, anti-rheumatic and chronic pain reliever, antimicrobial, anti-bloating and pain reliever. In terms of its chemical composition, sage leaves contain volatile essential oil, saponin and a bitter substance called picrosalvin with the property of facilitating digestion, diuretic, astringent and stopping the growth of bacteria and organic acids. Sage essential oil is amber and is very rich in terms of camphor content, and the amount of essential oil and the amount of cineole in the essential oil is the highest during the flowering and opening of the flower. The amount of cineole in the essential oil is about 25% in the essential oil of fresh dried branches. In the Middle Ages, sages of traditional European medicine used sage to treat constipation, cholera, colds and gout diseases, chronic rheumatism, Alzheimer's, liver disorders, epilepsy, nervous vertigo and paralysis, and to strengthen muscles. So far, several species of the genus Salvia, for example S. sclarea, S. hypoleuca, S. officinalis, S. syriaca, have been studied and identified and researched. Almost all types of sage are used in traditional medicine. Since ancient times, the leaves of the sclera plant have been used as a tonic and anticonvulsant. The conducted research considers the presence of some compounds in the essential oil of these plants, such as thujone, cineol and camphene, to be responsible for the antimicrobial, antioxidant and possibly anti-cancer properties of sage.

The tests performed in this research include physical and chemical tests (solubility, water vapor permeability, thickness and turbidity), mechanical tests (elongation to breaking point, tensile strength and Young's model), measurement of antioxidant property and antimicrobial activity. All experiments were performed in three replicates (3 subjects) in a completely randomized design. One-way analysis of variance (ANOVA) and average comparison of data were performed based on Tukey's test using Minitab18 software at a confidence level of 95%.

In this research, all mechanical parameters were significant (p<0.05) and the highest amount of tensile strength, elongation at break point and Young's model in the treatment was 2.5%. In the treatments of the films, the lowest solubility and permeability were observed in concentrations of 3.75% and 2.5% of essential oil, respectively. In the experiment, the turbidity of the 2.5% and 3.75% treatments was not significant (p > 0.05) and at the concentration of 1.25% essential oil, it had the highest value and thickness of 0.05 mm. The addition of plant essential oils was also significant on the antioxidant properties of edible films (p<0.05). Antimicrobial activity of the film was measured by disk diffusion method. In this experiment, the largest inhibition zone diameter in the concentration of 3.75% essential oil was related to Staphylococcus aureus with the average inhibition zone diameter of 11.11 mm. The average inhibition zone diameter for Pseudomonas aeruginosa and Escherichia coli was reported as 8.27 mm and 4.45 mm, respectively.

The results of this research showed that adding sage essential oil with a concentration of 3.75% to the gelatin film, in addition to preventing the growth and proliferation of bacteria, has enough power to increase the shelf life of perishable