Effect of Flavonoids on the Photooxidation of Fats ‐A Study on their Activity as Singlet Molecular Oxygen [O₂(¹δ)] Generators and Quenchers

Abstract

Susana C r i a d o , Sonia G. B e r t o l o t t i , A . T S o l t e r m a n n , I/: A v i l a a n d N . A . G a r c i a *The protective effect of the polyhydroxyflavones Fisetin and Baicalein on the sensitized [Oz('$)]mediated photooxidation of fats was investigated through a kinetic study. These flavonoids at concentrations in the order of a few ppm efficiently inhibit the photoperoxidation of linoleic acid, which was chosen as an example of photooxidizable fat. This property was attributed to the ability of Fisetin and Baicalein to quench photochemically generated Oz('4). The rate constants for such a process of quenching were 1.9 and 1.4 x lo8 M -k ' for Fisetin and Baicalein respectively. The ratio between the overall and the chemical rate constants were in the order of 0.01, indicating that the flavones are practically not consumed in the process of Oz('4) quenching. The presence of the -OH groups in the aromatic rings of the hydroxyflavones confer to these compounds the ability as Oz ('4) quenchers. The parent compound Flavone does not quench that oxygen excited species. Only Flavone generates Oz('4) upon direct irradiation, at 337 nm. in the absence of added sensitizers, with a quantum yield of 0.16. Fisetin and Baicalein were totally inefficient for such a process. This fact constitutes a very convenient property from the point of view of the protective (anti oxidative) activity of the hydroxyflavones. Fat Sci. Technol. 97. Jahrgang Nr. 718 lYY5 Fat SCI. Technol. 97. Jahrgang Nr. 718 1995

Antioxidant properties of natural flavonoids: quenching and generation of singlet molecular oxygen

“…According to the data in Table 1, FL compounds I‐IV are moderate to good O 2 ( 1 Δ g ) quenchers in Bz. The rate constants k t are in the range of those reported in the literature for different FL (Tournaire et al ., 1993; Criado et al ., 1995, 1996).…”

“…Sixteen shots were usually needed for averaging decay times, in order to get a good signal–noise ratio. This novel apparatus has been described previously (Criado et al ., 1995).…”

“…ADP was used as a reference (k rR = 5.5 × 10 7 M −1 s −1 as determined by TRPD). The photolyzer apparatus has already been described (Criado et al ., 1995). The disappearance of substrate and the reference compounds, either ADP or DMA, depending on the solvent employed, was monitored respectively by absorption spectroscopy, at 340 nm (compound III) and spectrofluorimetry employing 395 and 450 nm as excitation and emission wavelengths for the reference compounds.…”

“…Hence, it is of interest, from both the commercial and the scientific points of view, to investigate the ability of natural and synthetic antioxidants to retard the early stages of O 2 ( 1 Δ g )‐mediated unsaturated fatty acids photo‐oxidation. This consideration has induced different authors to explore the possible effect of flavonoids as protective agents against photo‐oxidation of fats (Tournaire et al ., 1993; Criado et al ., 1995, 1996). Particularly interesting are those flavonoid substances which occur naturally in plants.…”

Inhibitory Action of Oren-gedoku-to Extract on Enzymatic Lipid Peroxidation in Rat Liver Microsomes.

“…It has been reported that baicalein, which is present in Scutellariae Radix, one of the constituent herbs of TJ-15, and berberine, jatrorrizhine, magnoflorine, and palmatine, which are present in Coptidis Rhizoma, another constituent of TJ-15, function as efficient quenchers of singlet oxygen in vitro. 35,36) Accordingly, the possibility cannot be ruled out that TJ-15 inhibits enzymatic lipid peroxidation in rat liver microsomes by quenching singlet oxygen generated in the process of lipid peroxidation.…”