The use of Okra gum-Peppermint essential oil bioactive edible coating to improve shelf-life of buffalo meat

Meat and their products are highly sensitive to microbial growth and lipid oxidation development, which lead to economic losses and health hazards (Kiarsi et al., 2020). Edible coatings are currently receiving a great deal of attention as novel food packaging to increase the quality and shelf-life of various food products through preventing physical, chemical, and biological deteriorations (Barzegar et al., 2020). Okra (Ablemoschus esculentus) is an annual plant and rich in valuable nutrients such as vitamins and elements such as phosphorus, manganese, potassium and calcium and also contains phytosterols, tannins and carbohydrates. Okra contains large amounts of viscous gum with a thickening property. Edible coatings are able to carry active compounds such as antioxidants and antimicrobials, as well as nutrients and essential oils (Ashrafi Yorganloo and Gheybi, 2018). Peppermint (Mentha piperita) is one of the most widely used medicinal plants due to biological effects of its main components, especially menthol. Its essential oil is used as a flavoring in chewing gum, mint chocolate, medicines and toothpaste (Kazem Alvandi et al., 2010). The antimicrobial and antioxidant properties of peppermint essential oil have been investigated. To the best of our knowledge, there is no report in the literature regarding the effect of edible coating of Okra gum containing peppermint essential oil on meat quality and shelf life during refrigeration. This study is therefore aimed to develop a novel edible coating based on Okra gum-peppermint essential oil to improve the shelf life of buffalo meat slices.

Peppermint essential oil and Okra were purchased from Dezful and Ahvaz, respectively. The chemical compounds of the essential oil were identified and quantified by a gas chromatography coupled to a mass spectrometer. The total phenol content (Noshad et al., 2020), total flavonoid content (Rahmati‐Joneidabad and Alizadeh Behbahani, 2021), ABTS-radical scavenging effect (Hojjati and Alizadeh Behbahani, 2021), antimicrobial effect (Disc diffusion agar, well diffusion agar, and minimum inhibitory/bactericidal concentration) of the essential oil were determined. The oil (0, 0.5, 1, 1.5, 2%) was then added to Okra gum solution to prepare edible coatings for buffalo meat coating purposes. The physiochemical (pH, moisture content, peroxide value, and hardness), microbial (Total viable count, psychrotrophic count, E. coli, S. aureus, and Fungi count), color (L*, b*, and a*), and sensory (odor, color, appearance, texture, and overall acceptance) of buffalo meat slices were evaluated during storage period (10 days, 4 °C).

The essential oil contained menthol (47.17%) and menthone (23.29%) and its total phenolic content, flavonoid content, and ABTS radical scavenging effect were 77.20 mg GAE/g, 47.50 mg QE/g, and 62.60% respectively. The essential oil was also able to inhibit the growth of P. aeruginosa, E. coli, S. aureus, B. cereus, and B. subtilis. The functional groups of the compounds of peppermint essential oil were observed at 2955, 2923, 2870, 1711, 1455, 1369, 1247, 1044, 993, and 887 cm-1. The edible coating was able to prevent the pH increase in buffalo meat samples during storage. The control and samples coated with Okra gum containing 0, 0.5, 1, 1.5, and 2% essential oil had 11.26, 11.40, 6.40, 4.51, and 4.39% water loss during storage. The peroxide value of control and Okra gum+2%essential oil coated samples were increased by 7.33- and 2.28-folds, respectively, as the storage time increased up to 10 days. The lower oxidation development in the coated samples could be probably due to the low oxygen permeability of the coating and the antioxidant activity of the essential oil. Although the hardness of samples decreased during storage, the essential oil-rich coated samples had remarkably higher hardness values compared to the control sample, likely due to the inhibitory effect of the essential oil against the activity of endogenous proteolytic enzymes of the buffalo meat. The edible coatings loaded with higher concentration of the oil were more effective in inhibiting microbial growth in buffalo meat samples during cold storage. This could be attributed to the antimicrobial effect of the essential oil and the oxygen-barrier function of the edible coating. The L* and b* of the coated samples were also higher in comparison to the non-coated sample; whilst, they were generally less red, probably due to myoglobin conversion to metmyoglobin under low-oxygen pressure conditions of the edible coating, along with exudate accumulation in the coated buffalo meat samples. The coated samples with higher essential oil concentrations were also generally more acceptable in term of sensory properties. Generally, the sensory attributes were in good agreements with the chemical and microbial results; the lower the microbial growth and oxidation, the higher were the sensory properties.

The Okra gum-peppermint essential oil based edible coating could be introduced as a novel edible coating to inhibit the microbial growth and lipid oxidation of buffalo meat and increase its shelf-life and other food products. Keywords: Antimicrobial, Antioxidant, Chemical composition, Edible coating, Okra gum, Peppermint essential oil, Shelf-life.