title: Quantification of quercetin glycosides in 6 onion cultivars and comparisons of hydrolysis-HPLC and spectrophotometric methods in measuring total quercetin concentrations.
abstract: This study was performed to purify and quantify quercetin glycosides (QG) and aglycone (free) quercetin (Q) in 6 selected onion cultivars and to compare analytical approaches based on high-performance liquid chromatography (HPLC) and spectrophotometry for the quantification of total quercetin (TQ) concentrations. Individual mono- and di-glycoside Q compounds were purified using a semipreparative HPLC and identified by comparing spectral data and by confirming corresponding peaks of QG and Q after incomplete enzyme-hydrolysis. Purified QG were quantified as Q by enzyme-hydrolysis/HPLC. TQ concentrations obtained from 20 onion bulbs with enzyme-hydrolysis/HPLC, no-hydrolysis/HPLC, and a spectrophotometric method without prior hydrolysis were significantly correlated (r(2)= 0.99) and were about 15% higher, identical, or 10% less than those concentrations by a standard acid-hydrolysis/HPLC method, respectively. During enzyme-hydrolysis of onion extracts, progressive reduction of the QG and formation of the corresponding mono-glycosides and Q were monitored using an analytical HPLC. TQ ranged from 83 to 330 microg/g F.W. in 6 selected cultivars of long-day or short-day onions. Q3,4'G and Q4'G were the 2 major compounds and comprised approximately between 94% and 97% of TQ in onions.
authors.affiliation: Vegetable & Fruit Improvement Center, Dept. of Horticultural Science, Texas A&M Univ., College Station, TX 77843, USA. k-yoo@tamu.edu
authors.forename: Kil Sun
authors.initials: KS
authors.lastname: Yoo
authors.forename: Eun Jin
authors.initials: EJ
authors.lastname: Lee
authors.forename: Bhimanagouda S
authors.initials: BS
authors.lastname: Patil
mesh_terms: D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D005504:Food Analysis / Q000379:methods; D006027:Glycosides / Q000032:analysis* / Q000737:chemistry; D019697:Onions / Q000737:chemistry*; D011794:Quercetin / Q000032:analysis* / Q000737:chemistry; D013053:Spectrophotometry / Q000379:methods*
chemical_list: D006027:Glycosides; D011794:Quercetin