Improving the shelf life of lamb using edible coating based on Lepidium perfoliatum mucilage and Thymus carmanicus essential oil

Background and objectives: Its quality, nutritional properties, and physicochemical properties have made sheep meat very popular, and juiciness, smell, and taste are directly related to its quality. In spite of this, meat and meat products are susceptible to chemical and microbial spoilage during production, transportation, storage, and consumption. The high moisture and nitrogen content of meat, along with its suitable pH and fermentable carbohydrates, makes it an ideal environment for spoiling and poisonous bacteria and fungi. Food packaging can increase the shelf life of food products by inhibiting or delaying lipid oxidation and microbial growth, and edible packaging has been used to increase the shelf life of meat. Hydrocolloids are widely used in the food industry for various purposes such as gelling agents, stabilizers, and texture modifiers. Lepidium perfoliatum seed mucilage (LPSM) is used in traditional medicine to treat whooping cough, dry cough and lung infections and as a sedative, and due to its good physical, mechanical, and thermal properties, it can be used as a biodegradable packaging to improve the shelf life of various food products. However, polysaccharide-based coatings hardly have an antimicrobial or antioxidant effect, so antioxidant and antimicrobial compounds are usually included in edible coatings to improve their performance. Edible coatings enriched with plant essential oils, through controlling microbial growth, inhibiting lipid oxidation and improving the appearance of foods are widely used in food preservation.
Materials and methods: T. carmanicus plant was dried at room temperature and then powdered using a mill. After that, 50 g of the powder was transferred to the Clevenger device containing 750 ml of distilled water, and the extraction process was carried out by distillation with water for 3 h. The obtained essential oil (TCEO) was collected in a glass container and stored at 4 °C. Its phenol content (based on Folin-Ciocalteu method), flavonoid content (based on aluminum chloride colorimetry method), antioxidant activity (based on DPPH and ABTS radical scavenging methods), and antimicrobial activity (based on disc diffusion agar, well diffusion agar, minimum inhibitory concentration, and minimum bactericidal concentration methods) against pathogenic bacteria (Escherichia coli, Salmonella typhi, Pseudomonas aeruginosa, Listeria innocua, and Staphylococcus aureus) were evaluated. TCEO (0, 0.5, 1, 1.5%) was then added to the LPSM to prepare an edible coating to improve the shelf-life of lamb slices during cold storage (4 °C, 10 days). The physicochemical (pH, moisture content, hardness, peroxide value, and thiobarbituric acid value), microbial (total viable, psychrotrophic, E. coli, S. aureus, and fungi counts), and sensory (color, odor, texture, and overall acceptance) properties of the samples were evaluated during storage period.
Results and discussion: The essential oil with 0.96% extraction yield contained 52.22 mg GAE/g total phenol and 18.43 mg QE/g total flavonoids. The antioxidant activity of TCEO was found to be 357.13 and 312.18 μg/ml based on DPPH and ABTS radical scavenging methods. Based on disc and well diffusion agar tests, S. aureus and P. aeruginosa were the most sensitive and resistant strains to the essential oil, respectively. Increasing the storage time caused a significant increase in the total count of viable bacteria, psychrotrophic bacteria, E. coli, S. aureus, and fungi (p < 0.05); however, this value decreased significantly with the increase in the concentration of the essential oil in the edible coating. Moreover, the use of LPSM-TCEO edible coating inhibited the extensive changes in pH, moisture, peroxide value, and thiobarbituric acid value in lamb slices during storage period.