Quantification and analysis of anthocyanin and flavonoids compositions, and antioxidant activities in onions with three different colors

Onion (Allium cepa L.) is a very important vegetable crop widely cultivated throughout the world. In this study, we measured total anthocyanins and flavonols of onions of three colors. The fresh weight (FW) of total anthocyanins were (29.99±1.19), (9.64±1.30) and (0.75±0.40) mg 100 g−1 fruit in red, yellow and white onions, respectively. Likewise, the FW of total flavonoids were (111.10±5.98), (36.64±3.59), and 0 mg 100 g−1 in red, yellow and white, respectively. Four types of anthocyanins (delphinidin 3,5-diglycosides, cyanidin 3,5-diglycosides, cyanidin 3-glycosides and cyanidin 3-(6”-malonyl)-glucopyranoside) and two kinds of flavonoids (quercetin and quercetin 3-glycosides) were identified in two varieties (red and yellow bulb) of onions by HPLC/DAD-ESI/MS. The total polyphenol contents were also measured by means of Folin-Ciocalteu method. Moreover, all the concentrations of anthocyanins, flavonoids and polyphenols showed significantly positive correlations with antioxidant activities measured by DPPH·, ABTS·+ and FRAP assays. This study provided information on anthocyanin and flavonoids compositions that will be useful for onion breeding.