Of quercetin

Upon mashing, small amounts of tannin go into the solution from the malt, and later, during the boiling with hops, more tannin goes into the wort. Tannins from both barley and hops are leucoanthocyanin stmctures, in some cases they are derivatives of quercetin [117-39-5], cathechins are not found. The turbidities in beer, rich in leucoanthocyanins, are composed of peptones, peptides, and condensation products of the tannins of malts and hops. 

Average percentage of variation contributed by quercetin in each population. Average concentration of quercetin per population as % of total flavonoids. Frequency of the a allele in each population. 

One point should be raised that was not dealt with in the Lauranson and Lebreton (1991) paper. It would appear that the authors examined the concentration values of the individual flavonols at face value without considering likely or possible biosynthetic relationships. In particular, isorhamnetin is produced by 0-methylation of quercetin. Total quercetin produced would then be the sum of quercetin per se plus the amount of isorhamnetin present. This value, reflecting total 3, 4 -dioxygenated flavonols, would be the more accurate measure of allele frequency. 

Harborne, J. B. and Davenport, S. M. 1966. Identification of quercetin 5-methyl ether... 

FORMICA J V and reqelson w (1995) Review of the biology of quercetin and related bioflavonoids , Chem Toxicol, 33, 1061-80. 

The effect of quercetin on cell cycle progression and growth of hiunan gastric cancer cells , Febs Lett, 260, 10-13. 

Fig. 16.5 Synergistic regeneration of a-tocopherol by quercetin at a lipid-water interphase. a-tocopherol is reacting with a lipid peroxyl radical in a chain-breaking reaction. According to the standard reduction potential, the phenoxyl radical of quercetin can further be regenerated by ascorbate.

PEDRiELLi p and SKIBSTED L H (2002) Antioxidant syneigy and regeneration effect of quercetin, (-)epicatechin, and (+)-catechin on a-tocopherol in homogeneous solutions of peroxidating methyl linoleate, JAgric Food Chem, 50, 7138-44. 

PEDRIELLI p, PEDULLi G F and SKIBSTED L H (2001a) Antioxidant mechanism of flavonoids. Solvent effect on rate constant for chain-braining reaction of quercetin and epicatechin in autoxidation of methyl linoleate, JAgric Food Chem, 49, 3034-40. 

Awad, H. M. Boersma, M. G. Boeren, S. van Bladeren, P. J. Vervoort, J. Rietjens, I. M. C. M. Quenching of quercetin quinone/quinone methides by different thiolate scavengers stability and reversibility of conjugate formation. Chem. Res. Toxicol. 2003,16, 822-831. 

Naidu PS, Singh A, Kulkarni SK. D2 dopamine receptor and alpha2-adrenoreceptor-mediated analgesic response of quercetin. Indian J Exp Biol 2003 41 1400-1404. 

Lodi, F, R Jimenez, C Menendez, PW Needs, J Buaret, and E Perez-Vizcaino. 2008. Glucuronidated metabolites of the flavonoid of quercetin do not auto-oxidize, do not generate free radicals and do not decrease nitric oxide bioavailability. Planta Med 74(7) 741-746. 

E.S.B. Ferreira, A. Quye, H. McNab, A.N. Hulme, Photo oxidation products of quercetin and morin as markers for the characterisation of natural flavonoid yellow dyes in ancient textiles, Dyes in History and Archaeology 18, 63 72 (2002). 

Flavonoids bonded to fibres undergo photodegradation over the course of time their identification in historic textiles is thus often difficult. The analysis of a wool orange fibre (from a nineteenth century Aubusson tapestry) dyed with alum mordant and quercetin enabled the presence of quercetin (at m/z 301) and its decomposition products, 3,4-dihydroxybenzoic acid (at m/z 153) and methyl 3,4-dihydroxybenzoate (at m/z 167), to be confirmed. [30] The samples were hydrolysed with hydrochloric acid and analysed with RPLC MS. 

Harwood M, Danielewska-Nikiel B, Borselleca JF, Flamm GW, Williams GM and Lines TC. 2007. A critical review of the data related to the safety of quercetin and lack of evidence of in vivo toxicity, including lack of genotoxic/carcinogenic properties. Food Chem Toxicol 45 2179-2205. 

Mertens-Talcott SU, Bomser JA, Romero C, Talcott ST and Percival SS. 2005. Ellagic acid potentiates the effect of quercetin on p21wafl/cipl, p53, and MAP-kinases without affecting intracellular generation of reactive oxygen species in vitro. J Nutr 135 609—614. 

Mertens-Talcott SU, Talcott S T and Percival S S. 2003. Low concentrations of quercetin and ellagic acid synergistically influence proliferation, cytotoxicity and apoptosis in MOLT-4 human leukemia cells. J Nutr 133(8) 2669-2674. 

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. 

Boots AW, Haenen GRMM and Bast A. 2008. Health effects of quercetin From antioxidant to nutraceutical. 

The application of flavonoids for the treatment of various diseases associated with free radical overproduction is considered in Chapter 29. However, it seems useful to discuss here some studies describing the activity of flavonoids under certain pathophysiological conditions. Oral pretreatment with rutin of rats, in which gastric lesions were induced by the administration of 100% ethanol, resulted in the reduction of the area of gastric lesions [157]. Rutin was found to be an effective inhibitor of TBAR products in the gastric mucosa induced by 50%i ethanol [158]. Rutin and quercetin were active in the reduction of azoxymethanol-induced colonic neoplasma and focal area of dysplasia in the mice [159], Chemopreventive effects of quercetin and rutin were also shown in normal and azoxymethane-treated mouse colon [160]. Flavonoids exhibited radioprotective effect on 7-ray irradiated mice [161], which was correlated with their antioxidative activity. Dietary flavones and flavonols protected against the toxicity of the environmental contaminant dioxin [162], Rutin inhibited ovariectomy-induced osteopenia in rats [163],... 

Sanders et al. [133] found that although quercetin treatment of streptozotocin diabetic rats diminished oxidized glutathione in brain and hepatic glutathione peroxidase activity, this flavonoid enhanced hepatic lipid peroxidation, decreased hepatic glutathione level, and increased renal and cardiac glutathione peroxidase activity. In authors opinion the partial prooxidant effect of quercetin questions the efficacy of quercetin therapy in diabetic patients. (Antioxidant and prooxidant activities of flavonoids are discussed in Chapter 29.) Administration of endothelin antagonist J-104132 to streptozotocin-induced diabetic rats inhibited the enhanced endothelin-1-stimulated superoxide production [134]. Interleukin-10 preserved endothelium-dependent vasorelaxation in streptozotocin-induced diabetic mice probably by reducing superoxide production by xanthine oxidase [135]. 

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