Antimicrobial activities, phenolic and flavonoid contents, antioxidant and DNA protection of the internal and outer layers of Allium cepa L. from Iran

Allium cepa L., known as a wild onion in Iran with different high antioxidant and antimicrobial activities in internal and outer layers. The aim of this study was to assess phenolic and flavonoid contents as well as antioxidant and antimicrobial activities of the internal and outer layers of ten Iranian onions (Allium cepa L.) landrace and compare them with three hybrid onions. Results showed that the total phenolic, flavonoid contents and the antioxidant capacity of the onions ranged 18.76-65.25 (mg GAE/g DW), 0.06-1.92 (mg/g DW) and 10.34-40.54%, respectively. The results showed higher total phenolic and flavonoid content as well as antioxidant activity and protection of pBR322 DNA in the outer layer in compare to internal ones due to higher hydroxyl radicals. Based on the results, the present study showed that red onions such as landraces originated from Azarshahr and Nowshahr included the highest quantities of phenolic and flavonoid contents as well as antioxidant activity and DNA protection values. Inhibition zone and minimum inhibitory and minimum microbicidal concentration of internal layer of onion from Kahrizak were significantly different from others (p < 0.05). This research showed the potential of Iranian onions as a natural preservative and good antioxidant.