Onion waste as a rich source of antioxidants for meat products

Onion skin is a waste produced in thousands of tons annually in the European Union. It is a rich natural source of flavonoids and its water extracts (as an environmentally friendly solvent) could be used as an antioxidant material for meat products. Therefore, antioxidant properties of onion skin water extracts (OSWEs) were tested on cooked pork patties. Pork patties were divided into five treatments: control (no antioxidant), 10 and 20% (w/w) of yellow OSWE, and 10 and 20% (w/w) of red OSWE. Antioxidant activity, total polyphenols, thiobarbituric acid reactive substances (TBARS), and sensory analysis were assessed. Patties with added antioxidants showed significantly (P < 0.05) higher antioxidant activity and total polyphenol content. Samples with OSWEs, after 5-day storage (5°C), had significantly (P < 0.05) lower TBARS values compared to control. Two main phenolic compounds were identified in OSWEs by liquid chromatography – mass spectrometry using electrospray ionisation in negative mode: quercetin (m/z 301) and quercetin monoglucoside (m/z 463). OSWEs demonstrated the potential to be used as a source of natural antioxidants with strong antioxidant activity in meat products.