Quercetin content, fruit

Quercetin is the most common flavonol in fruits, elderberries (17.0 mg/100 g), lingonber-ries (12.6 mg/100 g), and cranberries (13.0 mg/100 g) being particularly rich sources. Berries and currants are also the fruits containing most kaempferol and myricetin. For example, these two flavonols account for 29 and 18%, respectively, of the total flavonol content of the bilberry. Although kaempferol and myricetin have also been identified in fruits such as peaches and pears, concentrations are generally too low to be readily quantified in the whole fruit. The skin of these fruits contains these flavonols in significant amounts however, their flesh, which constitutes >70% of the fresh weight, does not. Consequently, when analyzed as normally eaten only trace levels are present. 

Bilyk, A. and Sapers, G.M., Varietal differences in the quercetin, kaempferol, and myricetin contents of highbush blueberry, cranberry, and thornless blackberry fruits, J. Agric. Food Chem., 34, 585, 1986. 

Urinary excretion of quercetin increased significantly with dose and time after the consumption of fruit juice (blackcurrant and apple juice in a 1 1 mixture) in humans [75]. Ranges from 0.29-0.47% of ingested quercetin were found in the urine. The presence of quercetin in urine shows that it was absorbed by the gut, but the urinary content does not necessarily reflect absolute absorptive efficiency because absorbed quercetin may be metabolized (conjugated), stored and excreted through other routes such as the biliary tract. However, since quercetin is present in a variety of fruit and vegetables, plasma concentrations or urinary excretion of quercetin may potentially be useful as biomarkers of habitual intake of these foods. 

Sultana B, Anwar F (2008). Flavonols (kaempeferol, quercetin, myricetin) contents of selected fruits, vegetables and medicinal plants. Food Chemi, 108 879-884. 

The 3-glucuronide and 3-glucoside derivatives of kaempferol and quercetin are the main flavonoid constituents. They particularly accumulate in the external tissues of the fruit [36]. In a study of 20 cultivars the content varied from 21 to 174 mg/kg f.w. 

Apple polyphenols are present in different parts of the fruit. A major source is the skin, which contains all the flavonols and anthocyanins in addition to an important amount of dihydrochalcones. ° Phenolic acids are present in the flesh whereas most of the dihydrochalcones are in the core and the seeds. This distribution in different parts of the fruit also affects polyphenol concentration of apple juice where only small amounts of quercetin glycosides and dihydrochalcones are present. However, polyphenol content is also affected by the technological procedure. The oxidative conditions and the clarification process during the production of clear apple juice reduces the phenolic content. In contrast, the anaerobic conditions and the lack of a clarification step during cloudy apple juice production prevents an important loss of polyphenols. ... 

Most native Brazilian fruits have high flavonol content, mainly quercetin derivatives, when compared to well-known fruit sources such as apples (Genovese et al. 2008 Aheme and O Brien 2002). For example, Mana-cubiu Solarium sessiliflorum Dunal) was shown to be a very rich source of hydroxyciimamic acids, typical of members of the Solanaceae family, and also exhibited high antioxidant capacity by the ORAC method. Catechin and epicatechin were detected in tucuma (79 mg/100 g DW) and graviola Annona muricata L) (31 mg/100 g of sample DW) (Genovese etal. 2008). 

Verbenic et al., [15] measured the content in anthocyanins, quercetin and sugars in the fruit of two cultivars and three elderberry selections. Their results show that the leading European cultivar is "Haschberg has significantly higher amounts of total anthocyanins given to other cultivars/selections but lower concentrations of secondary metaboHtes than some selections [15]... 

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