Quercetin determination

Fig. 1. Comparison between natural logarithm of sum of gallic acid, (+)-catechin, (-)-epicatechin, irans-resveratrol, ci resveratrol and quercetin, determined using HPLC and TAPcl. All wine samples included.

For aqueous solutions, ascorbate can be included in the hierarchy, while a-tocopherol has to be replaced by its water-soluble analogue trolox, which is often assumed to have the same standard reduction potential. The ordering of the antioxidants based on the two different determinations of E in water is rather similar, and it should be noted that ascorbate is the antioxidant which will regenerate the other antioxidants, with the ascorbate itself ending up being oxidised. In contrast to what was observed for DMF, the ordering in water predicts that quercetin could regenerate a-tocopherol from its oxidised form. 

Total flavonoid content. Quantitative analysis of flavonoids depends on the objective of the study. Colorimetric estimation of total flavonoid content is measured by the aluminum chloride colorimetric assay (Jia and others 1999 Chang and others 2002). The total flavonoid content measured in this way is normally expressed in equivalent values of a standard flavonoid, often catechin or quercetin equivalents. Not all subgroups of flavonoids can be quantified by colorimetric methods however, total anthocyanin content is determined using the pH-differentiation method (Boyles and others 1993). 

Careri M, Elviri L, Mangia A and Musci M. 2000. Spectrophotometric and coulometric detection in the high-performance liquid chromatography of flavonoids and optimization of sample treatment for the determination of quercetin in orange juice. J Chromatogr A 881 449-460. 

Red wine contains quercetin, rutin, catechin, and epicatechin, among other flavonoids (Frankel and others 1993). Quercetin and other phenolic compounds isolated from wines were found to be more effective than a-tocopherol in inhibiting copper-catalyzed LDL oxidation. It has been determined that quercetin has also several anti-inflammatory effects it inhibits inflammatory cytokine production (Boots and others 2008), inducible NO synthase expression and activation of inflammatory transcription factors (Hamalainen and others 2007), and activity of cyclooxygenase and lipooxygenase (Issa 2006), among others. 

The effects of flavonoids on in vitro and in vivo lipid peroxidation have been thoroughly studied [123]. Torel et al. [124] found that the inhibitory effects of flavonoids on autoxidation of linoleic acid increased in the order fustin < catechin < quercetin < rutin = luteolin < kaempferol < morin. Robak and Gryglewski [109] determined /50 values for the inhibition of ascorbate-stimulated lipid peroxidation of boiled rat liver microsomes. All the flavonoids studied were very effective inhibitors of lipid peroxidation in model system, with I50 values changing from 1.4 pmol l-1 for myricetin to 71.9 pmol I 1 for rutin. However, as seen below, these /50 values differed significantly from those determined in other in vitro systems. Terao et al. [125] described the protective effect of epicatechin, epicatechin gallate, and quercetin on lipid peroxidation of phospholipid bilayers. 

Another study used RP-HPLC for the determination of quercetin, luteolin, apigenin and kaempferol in honey and various other food products. The amounts of flavonoids found are compiled in Table 2.58. The data demonstrate again that the flavonoid content and profile are highly different in various foods and food products which has to be taken into consideration in the design of special diets [163],... 

Another RP-HPLC method was applied for the determination of gallic acid, trans-veratrol, quercetin and rutin in red wines. Samples of wines were filtered and injected into... 

The amounts of analytes are compiled in Table 2.74. The results indicated that the concentration of polyphenols in red wines depends on both the grape variety and on the exogenous factors. The validation parameters of the method were good, the recoveries were in each case over 98 per cent, the coefficients of variation were between 1.3 per cent and 4.3 per cent, and the limit of detection ranged from 10/rg/l to 0.1mg/l. It was stated that the method is suitable for the determination of silbene compounds and quercetin in red wines [194],... 

Another study employed a similar RP-HPLC method for the determination of trails- and d.v-rcsvcratrol, catechin, epicatechin, quercetin and rutin in wines and musts. Wine samples were filtered and diluted when necessary and used for analysis without any other pretreatment. Separation was performed in an ODS column (150 X 4 mm i.d. paricle size 5 71m) at ambient temperature. The gradient began with ACN-5 per cent aqueous acetic acid (9 91, v/v) for 0-10 min to 25 75 in 1 min hold for 11 min to 70 30 in 1 min, hold for 5 min. The flow rate was 1 ml/min. Analytes were detected by DAD. Fluorescence detection used 280/315 nm (excitation/emission) for catechin and epicatechin 314/370 nm for fims-resveratrol and 260/370 nm for d.v-rcsvcratrol. Chromatograms of a red wine sample obtained at different... 

The content of quercetin in human plasma after consuming canned green tea has been determined by RP-HPLC and electrochemical detection. Hydrolysis of quercetin in green tea samples was carried out by mixing 1 ml of tea with 1.5 ml of mobile phase, ultrasoni-cated for 3 min, mixed again with 0.5 ml of 6 M HC1 and heated at 90°C for 2 h. After cooling the sample was filtered, diluted 100 times and injected into the column. 

A. Jamshidi, M. Adjvadi and S.W. Husain, Determination of kaempferol and quercetin in the extract of Ginkgo biloba leaves by high-performance thin-layer chromatography (HPTLC). J. Plan. Chromatogr.—Mod. TLC. 13 (2000) 57-59. 

D. Jin, H. Hakamata, K. Takahashi, A. Kotani and F. Kusu, Determination of quercetin in human plasma after ingestion of commercial canned green tea by semi-micro HPLC and electrochemical detection. Biomed. Chromatogr. 18 (2004) 662-666. 

There are a few values in the literature relating to the cations Zr " " and Ge. In the zirconium case log Ki and log K2 values are reported for formation of quercetin complexes, but as these were obtained in 0.5 M HCl these values may well apply to ternary chloride-containing species (225). Equilibrium constants have been determined for reaction of two or of three maltol ligands with Ge(0H)4 (149), but these values are not comparable with values in the Tables elsewhere in this section, since these all refer to complex formation from aqua-cations or oxoaqua-cations. 

Opioid A recent study has shown activity of hypericum extracts at opioid receptors (Simmen et al. 1998). Extracts displace naloxone from p and x opioid receptors in the micromolar range (IC50 25 and 90 pg/ml, respectively). In contrast, extracts of the sedative herb Valeriana officinalis do not have this effect. This effect is due to unidentified constituents and not by the flavonoids quercetin or kaemferol. Opioids are known to have effects on emotion, so it is conceivable that activity of hypericum at p and k receptors contributes to its therapeutic effects (Gerra et al. 1998 Tejedor-Real et al. 1995 Walker and Zacny 1998). Although they are not conventional treatment for depression, opioids such as buprenorphine have been effective in treatment of refractory depression (Bodkin et a. 1995). However, for any further conclusions to be drawn, it would be necessary to further e uddate the opioid effects of hypericum to determine what functional effect, if any, hypericum has on the receptors. 

Rothwell. J.A.. Day. A.J.. and Morgan. M.R.A. Experimental determination of octanol-water partition coefficients of quercetin and related flavonoids. J. Agric. Food Chem., 53(ll) 4355-4360. 2005. 

Other applications include the online coupling of capillary isotachophoresis and CZE for the quantitative determination of flavonoids in Hypericum perforatum (Guttiferae) leaves and flowers. This method involved the concentration and preseparation of the flavonoid fraction before introduction into the CZE capillary. The limit of detection for quercetin 3-0-glycosides was 100 ng/ml. ... 

Mendoza-Wilson, A.M. and Glossman-Mitnik, D., CHIH-DFT determination of the molecular structure, infrared and ultraviolet spectra of the flavonoid quercetin, J. Mol. Struct. (Theochem.), 681, 71, 2004. 

Mullen, W., Graf, B.A., Caldwell, S.T., Hartley, R.C., Duthie, G.G., Edwards, C.A., Lean, M.E., and Crozier, A., Determination of flavonol metabolites in plasma and tissues of rats by HPLC-radiocounting and tandem mass spectrometry following oral ingestion of [2- C]quercetin-4 -glucoside, J. Agric. Food Chem., 50, 6902, 2002. 

Animal studies In the study by Pietta et al. (39), a single dose of ginkgo leaf extract (EGb 761) was administered orally to rats. Metabolites found in the urine represented less than 40% of the flavonoids administered. The presence of phenylalkyl acids in the rat urine but not in the human urine (33,39) indicates that the flavonols were more extensively metabolized in humans than in rats. In the study by Watanabe et al. (40), mice received a diet containing ginkgo leaf extract (EGb761 36mg/kg daily) or a standard diet without the extract for four weeks. Afterwards, plasma levels of quercetin (12.0ng/mL vs. 4.8ng/mL), kaempferol (7.0ng/mL vs. 3.2 ng/ mL), and isorhamnetin (49.6ng/mL vs. Ong/mL) in both treatment groups were determined. The study indicates that these compounds can be absorbed intact into the blood stream. 

Watson DG, Oliviera EJ. Solid-phase extraction and gas chromatography-mass spectrometry determination of kaempferol and quercetin in human urine after consumption of Ginkgo biloba tablets. J Chromatogr B Biomed Sci Appl 1999 723 203-210. 

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