On the stability of the bioactive flavonoids quercetin and luteolin under oxygen-free conditions

0375920 - ÚFCH JH 2013 RIV DE eng J - Journal Article
Ramešová, Šárka - Sokolová, Romana - Degano, I. - Kocábová, Jana - Žabka, Ján - Gál, Miroslav
On the stability of the bioactive flavonoids quercetin and luteolin under oxygen-free conditions.
Analytical and Bioanalytical Chemistry. Roč. 402, č. 2 (2012), s. 975-982. ISSN 1618-2642. E-ISSN 1618-2650
R&D Projects: GA ČR GA203/09/1607
Institutional research plan: CEZ:AV0Z40400503
Keywords : flavonoids * antioxidants * stability
Subject RIV: CF - Physical ; Theoretical Chemistry
Impact factor: 3.659, year: 2012

The natural flavonoid compounds quercetin (3,3',4',5,7-pentahydroxyflavone) and luteolin (3',4',5,7-tetrahydroxyflavone) are important bioactive compounds with antioxidative, anti-allergic, and anti-inflammatory properties. However, both are unstable when exposed to atmospheric oxygen, which causes degradation and complicates their analytical determinations. The oxidative change of these flavonoids was observed and followed by UV-visible spectrophotometry, both in aqueous and ethanolic solutions. The distribution of the degradation products in aqueous media was monitored by LC-MS and LC-DAD analysis. The amounts of oxidative reaction products increase with the exposure time. The oxidative degradation reduces the pharmacological efficiency of these antioxidants and renders analytical determination inaccurate. The oxidative changes in flavonoid test solutions can explain the inconsistent dissociation constants reported in the literature. Dissociation constants of quercetin and luteolin were determined both by alkalimetric titration and by UV-visible spectrophotometry under deaerated conditions. The values pK (1) = 5.87 +/- 0.14 and pK (2) = 8.48 +/- 0.09 for quercetin, and pK (1) = 5.99 +/- 0.32 and pK (2) = 8.40 +/- 0.42 for luteolin were found.
Permanent Link: http://hdl.handle.net/11104/0208457