Flavonoids from the Red Leaf Sheaths of Allium fistulosum ‘Hitachi-benikko’ (Ibaraki’s Specialty Red Welsh Onion Cultivar) and Their Antioxidant Activity

Abstract

Red welsh onion (Allium fistulosum L.) ‘Hitachi-benikko’, which has red leaf sheaths, was bred by Ibaraki Agricultural Center as a commercial vegetable in Ibaraki Prefecture. In this study, four anthocyanins including a novel glycoside [cyanidin 3-O-(3″-O-acetyl-6″-O-malonyl)-glucoside] and five flavonols were isolated and characterized by chemical and spectroscopic methods. The novel anthocyanin was the main component in the underground part of ‘Hitachi-benikko’. Of these flavonols, four were identified as quercetin and its glycosides, which are known to exhibit marked antioxidant activity. Furthermore, we measured the polyphenol content and antioxidant activity (H-ORAC) of the aerial and underground parts of ‘Hitachi-benikko’ and compared them with those of another general welsh onion cultivar. As the results, the reddish underground parts of ‘Hitachi-benikko’ showed higher polyphenol contents and antioxidant activities than the aerial parts of ‘Hitachi-benikko’ and those of the general welsh onion cultivar. These results promote the value of red welsh onion cultivar ‘Hitachi-benikko’ as a vegetable.