Evaluation of antioxidant and antimicrobial activity of Oregano essential oil and its effect on oxidative stability of silver carp (Hypophthalmichtys molitrix) fish oil in water emulsion

Fish oil is a rich source of omega-3 fatty acids, which is recommended for prolonged use due to beneficial nutritional effects and the prevention of heart disease and disorders. However, high unsaturation of this oil makes it susceptible to oxidation. In the present study, antioxidant activity of Origanum vulgare L. essential oil was evaluated by DPPH assay and its antimicrobial activity was determined by measuring the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of Escherichia coli, Staphylococcus aureus, Listeria monocytogenes and Pseudomonas aeruginosa. Then, Origanum vulgare L. essential oil as natural antioxidant and alternative of synthesis ones, for stabilizing silver carp fish oil in water emulsion was used. So, after determining the fatty acid profile of the oil, different concentrations of the essential oil added to emulsion and stored at 4°C and 25°C and monitored in term of hydroperoxides, conjugated diene, conjugated triene and thiobarbituric acid. The results showed that 2400 ppm of Origanum vulgare L. had the most DPPH inhibitory power with 53.33% and MIC and MBC values of Origanum vulgare L. essential oil in gram-negative bacteria were more than gram-positive bacteria. Moreover, various concentrations of the essential oil prevented lipid oxidation of fish oil in water emulsions. So that, at 2400 ppm, had even better performance than synthetic antioxidant, TBHQ. Therefore, the natural Origanum vulgare L. essential oil due to its antioxidant and antimicrobial properties can be used as an alternative to synthetic types in various food systems.