title: Evaluation of total phenolics, flavonoids and antioxidant activity of 18 Korean onion cultivars: a comparative study.
abstract: 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Molecular Biotechnology, Konkuk University, Seoul, 143-701, Republic of Korea.
authors.forename: Kavita
authors.initials: K
authors.lastname: Sharma
authors.forename: Awraris D
authors.initials: AD
authors.lastname: Assefa
authors.forename: Seol
authors.initials: S
authors.lastname: Kim
authors.forename: Eun Young
authors.initials: EY
authors.lastname: Ko
authors.forename: Eul Tai
authors.initials: ET
authors.lastname: Lee
authors.forename: Se Won
authors.initials: SW
authors.lastname: Park
mesh_terms: D000975:Antioxidants / Q000032:analysis*; D005419:Flavonoids / Q000032:analysis*; D044948:Flavonols / Q000032:analysis; D019697:Onions / Q000737:chemistry* / Q000254:growth & development; D010636:Phenols / Q000032:analysis*; D017440:Photoperiod; D010936:Plant Extracts / Q000737:chemistry; D018517:Plant Roots / Q000737:chemistry; D011794:Quercetin / Q000032:analysis; D056910:Republic of Korea; D013045:Species Specificity
chemical_list: D000975:Antioxidants; D005419:Flavonoids; D044948:Flavonols; D010636:Phenols; D010936:Plant Extracts; D011794:Quercetin; C432511:isorhamnetin 3-O-glucoside
keywords: antioxidant; flavonols; onion; total flavonoids; total phenolics