Evaluation of total phenolics, flavonoids and antioxidant activity of 18 Korean onion cultivars: a comparative study

BACKGROUND Onion is undoubtedly one of the major sources of flavonoids. However, there exists a varietal difference in composition, concentration and beneficial activities of onion, on the basis of cultivars, day length sensitivity/ripening and types. To characterise such differences, 18 onion cultivars from Korean were evaluated for their total phenolics, flavonoids and antioxidant activity. Simultaneous quantification of quercetin, quercetin‐3,4′‐ O ‐diglucoside, quercetin‐4′‐ O ‐monoglucoside and isorhamnetin‐3‐glucoside was made in methanol and 75% ethanol . RESULTS Total phenolic content was examined spectrophotometrically with the Folin–Ciocalteu phenol reagent and total antioxidant activity were studied by the ferric reducing antioxidant power ( FRAP ) and diphenyl picryl hydrazyl ( DPPH ) methods. The cultivar ‘Sunpower’ showed the highest level of total phenolics [5016 ± 30.0 µg gallic acid equivalents g −1 dry weight ( DW )] and flavonoids (2873.95 ± 60.01 µg Q g −1 DW ) among the 18 cultivars in methanol. However, there were fewer total phenolics and flavonoids in ethanol extracts. The antioxidant activity for cultivar Sunpower was highest in ethanol extracts 24.12 ± 1.00 and 16.13 ± 0.35 µmol L −1 Trolox equivalents g −1 DW with FRAP and DPPH , respectively . CONCLUSION Among the 18 cultivars, Sunpower is the most promising in terms of total phenolics, total flavonoids and antioxidant activity. Our results suggest that day length sensitivity/ripening among the cultivars do not play any significant role for high values of total phenolics, flavonoids and antioxidant activity. © 2013 Society of Chemical Industry