Investigation of phenolic compounds and antioxidant activity in red and yellow onions and a synergistic utilization of skin extract in modified atmosphere packaging of salmon (Salmo salar)

This study investigated potentially synergetic effects of red onion skin extract and modified atmosphere packaging (MAP) on lipid oxidation of salmon. The skin and flesh of red and yellow onions were extracted with water at 25°C, 45°C, 65°C and 90°C, ethanol and acetone in water solutions. Total anthocyanin and polyphenol levels and antioxidant capacity were determined after extraction. Minced salmon samples were mixed with red onion skin extract (ROSE) and packaged under MAP at different O2 concentrations (0%, 5%, 10% and 15% of total package gas composition) with 40% CO2 and balance N2. Polyphenol recovery and antioxidant capacity increased for each sample as the extraction temperature increased with hot water use. Water extraction at 90°C provided higher extraction yields than ethanol and acetone in water solutions. The ROSE treatment of fish with MAP reduced lipid oxidation rates as evidenced by a decrease in peroxide value (43%) and thiobarbituric acid reactive substance (TBARS) (30%). The ROSE might effectively suppress the free radicals in a MAP system. A skin extract and MAP application might increase the shelf life of salmon. Hot water use increased the antioxidant activity of onion skin extracts. Onion skin decreased peroxide values and TBARS of salmon in MAP. Waste of onion skin can be converted to use as a natural polyphenol extract.