title: Characterization and quantification of flavonoids and hydroxycinnamic acids in curly kale (Brassica oleracea L. Convar. acephala Var. sabellica) by HPLC-DAD-ESI-MSn.
abstract: Kale is a leafy green vegetable belonging to the Brassicaceae family, a group of vegetables including cabbage, broccoli, cauliflower, and Brussels sprouts, with a high content of health-promoting phytochemicals. The flavonoids and hydroxycinammic acids of curly kale ( Brassica oleracea L. ssp. oleracea convar. acephala (DC.) Alef. var. sabellica L.), a variety of kale, were characterized and identified primarily through HPLC-DAD-ESI-MS(n) analysis. Thirty-two phenolic compounds including glycosides of quercetin and kaempferol and derivatives of p-coumaric, ferulic, sinapic, and caffeic acid were tentatively identified, providing a more complete identification of phenolic compounds in curly kale than previously reported. Moreover, three hydroxycinnamic acids and one flavonoid with an unusual high grade of glycosylation, quercetin-3-disinapoyl-triglucoside-7-diglucoside, have been tentatively identified for the first time. The influence of different extraction conditions (extraction method, solvent type, solvent/solid ratio, and duration of extraction) was investigated. The total flavonol and hydroxycinnamic acid contents in curly kale determined as rutin equivalents (RE) were 646 and 204 mg of RE/100 g of fresh weight (fw), respectively. The contents of individual flavonoids ranged from 2 to 159 mg of RE/100 g of fw, with main compounds kaempferol-3-sinapoyl-diglucoside-7-diglucoside (18.7%) and quercetin-3-sinapoyl-diglucoside-7-diglucoside (16.5%). After acidic hydrolysis, two flavonol aglycones were identified in curly kale, quercetin and kaempferol, with total contents of 44 and 58 mg/100 g of fw, respectively.
authors.affiliation: Nofima Mat AS, Osloveien 1, N-1430 Aas, Norway. helle.olsen@nofima.no
authors.forename: Helle
authors.initials: H
authors.lastname: Olsen
authors.forename: Kjersti
authors.initials: K
authors.lastname: Aaby
authors.forename: Grethe Iren A
authors.initials: GI
authors.lastname: Borge
mesh_terms: D001937:Brassica / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D003373:Coumaric Acids / Q000032:analysis*; D005419:Flavonoids / Q000032:analysis*; D006027:Glycosides / Q000032:analysis; D006868:Hydrolysis; D044949:Kaempferols / Q000032:analysis; D010636:Phenols / Q000032:analysis; D011794:Quercetin / Q000032:analysis; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*
chemical_list: D003373:Coumaric Acids; D005419:Flavonoids; D006027:Glycosides; D044949:Kaempferols; D010636:Phenols; C006552:kaempferol; D011794:Quercetin