ABSTRACT:Human subjects drank coffee containing 412 mol of chlorogenic acids, and plasma and urine were collected 0 to 24 h after ingestion and were analyzed by high-performance liquid chromatographymass spectrometry. Within 1 h, some of the components in the coffee reached nanomole peak plasma concentrations (C max ), whereas chlorogenic acid metabolites, including caffeic acid

It is essential to have a thorough knowledge of the bioavailability and metabolism of dietary flavonols to understand their role in disease prevention. Lightly fried onions containing 275 mmol flavonols, principally quercetin-4 0 -glucoside and quercetin-3,4 0 -diglucoside, were fed to healthy human volunteers and plasma and urine were collected over a 24 h period. Samples were analysed by HPLC with diode array and tandem mass spectrometric detection. Five flavonol metabolites, quercetin-3 0 -sulphate, quercetin-3-glucuronide, isorhamnetin-3-glucuronide, a quercetin diglucuronide and a quercetin glucuronide sulphate, were detected in plasma in quantifiable amounts with trace quantities of six additional quercetin metabolites. Sub-micromolar peak plasma concentrations (C max ) of quercetin-3 0 -sulphate, quercetin-3-glucuronide, isorhamnetin-3-glucuronide and quercetin diglucuronide were observed 0.6 -0.8 h after ingestion. In contrast, the C max of quercetin glucuronide sulphate was 2.5 h. The elimination half-lives (t 1/2 ) of quercetin-3 0 -sulphate, quercetin-3-glucuronide and quercetin diglucuronide were 1.71, 2.33 and 1.76 h respectively, while the t 1/2 of isorhamnetin-3-glucuronide was 5.34 h and that of quercetin glucuronide sulphate was 4.54 h. The profile of metabolites excreted in urine was markedly different to that of plasma with many of the major urinary components, including quercetin-3 0 -glucuronide, two quercetin glucoside sulphates and a methylquercetin diglucuronide, absent or present in only trace amounts in the bloodstream indicative of substantial phase II metabolism. Total urinary excretion of quercetin metabolites was 12·9 mmol, corresponding to 4·7 % of intake. If these samples had been subjected to hydrolysis, as in many previous studies, only quercetin and isorhamnetin would have been detected and quantified. The bioactivity of these metabolites should be considered. Flavonols are polyphenolic C6-C3-C6 compounds which, along with other flavonoids and phenolics, occur widely in plants and plant-derived foods and beverages (Crozier et al. 2006). They have several potential nutritional and health-promoting roles in the human body but there is still much to be learnt about their bioavailability and, in particular, which metabolites appear in plasma and in what amounts. This information is essential to understanding the potential role of these compounds in reducing CHD and cancer as it is likely that the metabolites do not have the same bioactivity as the parent compounds. To gain a full picture of the absorption and metabolism of flavonols it is essential to be able to detect and quantify all the major metabolites in plasma and urine and this requires the use of appropriate analytical methodology such as HPLC with tandem MS (MS 2 ). Quercetin is the major flavonol in many foods including onions which consistently contain high levels of flavonols in the form of quercetin-3,4 0 -diglucoside (I in Fig. 1), quercetin-4 0 -glucoside (II in Fig. 1), and smaller amounts of other conjugates incl...

The flavonol contents of 20 varieties of tomato fruit were investigated in relation to variety, size, season, and country of origin. Ten commonly consumed tomato-based food products were also assessed. Free and conjugated flavonols were identified and quantified using reversed-phase HPLC. Ninety-eight percent of flavonols detected in tomatoes were found to occur in the skin. Tomatoes contained, primarily as conjugates, quercetin and kaempferol. The main quercetin conjugate was identified as rutin (quercetin 3-rhamnosylglucoside) by LC-MS. The total flavonol content of the different varieties of tomato that were analyzed varied from 1.3 to 22.2 microgram/g of fresh weight (fw). Smaller cherry tomato fruits originating from warm sunny climates, such as Spain and Israel, were found to contain the highest concentration of flavonols. Among the tomato-based products investigated, tomato juice and tomato purée were rich in flavonols, containing 14-16 microgram/mL and 70 microgram/g fw, respectively. In contrast to fresh tomatoes, most tomato-based products contained significant amounts of free flavonols.

Analysis of extracts of Glen Ample raspberries (Rubus idaeus L.) by gradient, reverse phase HPLC with diode array and tandem mass spectrometry identified eleven anthocyanins, including cyanidin-3-sophoroside, cyanidin-3-(2(G)-glucosylrutinoside), cyanidin-3-glucoside, cyanidin-3-rutinoside, pelargonidin-3-sophoroside, pelargonidin-3-(2(G)-glucosylrutinoside), and pelargonidin-3-glucoside. Significant quantities of an ellagitannin, sanguiin H-6, with an M(r) of 1870 were detected along with lower levels of a second ellagitannin, lambertianin C, which has an M(r) of 2804. Other phenolic compounds that were detected included trace levels of ellagic acid and its sugar conjugates along with one kaempferol- and four quercetin-based flavonol conjugates. Fractionation by preparative HPLC revealed that sanguiin H-6 was a major contributor to the antioxidant capacity of raspberries together with vitamin C and the anthocyanins. Vasodilation activity was restricted to fractions containing lambertianin C and sanguiin H-6.

The antioxidant capacity (AOC) of black currant, blueberry, raspberry, red currant, and cranberry extracts was determined using the FRAP assay. In addition, the vitamin C content of the berries was determined and phenolic and polyphenolic compounds in the extracts were analyze by reversed-phase HPLC-PDA-MS(3) and by reversed-phase HPLC-PDA with an online antioxidant detection system. A complex spectrum of anthocyanins was the major contributor to the AOC of black currants and blueberries, whereas the lower AOC of red currants and cranberries was due mainly to a reduced anthocyanin content. Raspberries also had a lower anthocyanin content than black currants and blueberries, but there was only a slight decline in the AOC because of the presence of the ellagitannins sanguin H-6 and lambertianin C, which were responsible for 58% of the HPLC-AOC of the berries. Vitamin C was responsible for 18-23% of the HPLC-AOC of black currants, red currants, and cranberries and for 11% of that of raspberries but did not contribute to the AOC of the blueberry extract that was examined. Seven percent of the HPLC-AOC of the cranberry extract was attributable to procyanidin dimers. However, the contribution of polymeric proanthocyanidins to the AOC of the five berries was not determined as when analyzed by reversed-phase HPLC these high molecular weight flavan-3-ols are either retained by the column or eluted as a broad unresolved band.

No abstract

Cranberry juice consumption did not alter blood or cellular antioxidant status or several biomarkers of lipid status pertinent to heart disease. Similarly, cranberry juice had no effect on basal or induced oxidative DNA damage. These results show the importance of distinguishing between the in vitro and in vivo antioxidant activities of dietary anthocyanins in relation to human health.

Rats were fed ag rape seed extract (GSE) containing ( þ )-catechin,( 2 )-epicatechin and dimers, trimers, tetramers and polymeric procyanidins. Liver, kidney, brain and gastrointestinal (GI) tract together with plasma, urine and faeces were collected over a24h period and their flavan-3-ol content was analysed by HPLC with tandem mass spectrometry and diode array detection. Small amounts of the GSE flavan-3-ols moved out of the stomach and into the duodenum/jejunum, and to ag reater extent the ileum 1h after ingestion, and into the caecum after 2h with relatively small amounts being detected in the colon after 3h.T he GI tract contained the parent GSE flavan-3-ols and procyanidins with only trace amounts of metabolites and there were no indications that proanthocyanidins were depolymerised in the GI tract releasing monomeric flavan-3-ols.Plasma contained exclusively catechin glucuronidesand methylated glucuronide metabolites which were also detected in the liver and kidneys. These metabolites were also present in urine together with sulphated metabolites and low amounts of the procyanidin dimers B 1 ,B 2 ,B 3 and B 4 as well as the trimer C 2 and an unknown GSE trimer. The amounts of ( þ )-catechin and ( 2 )-epicatechin metabolitesexcreted in urine relative to the quantity of the monomers ingested were 27 and 36 %, respectively, after 24 h. This is similar to the levels of urinary excretion reported to occur by other investigators after feeding ( 2 )-epicatechin to rats and provides further, albeit indirect, evidence that the procyanidinoligomers in the GSE were not depolymerised to monomers to any extent after ingestion. No convincing analytical data were obtained for the presence of flavan-3-ol metabolites in the brain.