Quercetin glycoside flavonols

Figure 8.1 Structures of main flavonol aglycones and quercetin glycosides present in plant foods.

Hypericum perforatum contains several flavonoids. The largest group of them are the common quercetin-based flavonol glycosides, hyperoside 42, rutin 41, quercitrin 39 and isoquercitrin 40 [85]. Among the aglycones, quercetin 38, kaempferol 43, luteolin 44 and myricetin 45 have been reported to occur [86]. Berghofer and Holzl found two biflavones in... 

Brassica oleracea varieties contain kaempferol and quercetin glycosides [43 57]. In addition, apigenin and luteolin have been reported in broccoli. The flavonol content of the edible parts of cabbage, cauliflower and kohlrabi is very low. Brussels sprouts, broccoli and Chinese cabbage have been reported to contain 15-60 mg/kg f.w. of... 

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. ... 

Sixteen flavonol glycosides (mainly mono-, di-, and triglycosides of quercetin and kaempferol) have been detected in hop [31]. Although boiling can extract 91% of the kaempferol and 88% of the quercetin glycosides, only a few ppms of flavonols are found in the final beer (Fig. 75.3) [8, 11, 13, 67, 68]. 

The absorption of quercetin glycosides is complex. Flavonol-rich foods contain a mixture of many different types of conjugate, aU of which may be absorbed in a different manner. Quercetin rhamnoglucosides such as rutin, commonly foimd in plant foods, appear only to be absorbed in the large intestine after hydrolysis by the colon microflora. Late absorption in the gastrointestinal tract leads to... 

The main substrates of polyphenol oxidases in apples are hydrox-ycinnamic acid derivatives, especially caffeic add depsides, such as chlorogenic acid, and some groups of flavonoid compounds, such as flavan-3-ols, flavonols, dihydrochalcones and (in red-skinned apple varieties) also anthocyanins. In the flesh of apples, the main phenohcs are chlorogenic (3-caffeoylquinic) add, flavan-3-ol epicatechm, and procyanidin B2 representing condensed tannins. These three compounds represent more than 90% of the phenolic compounds present. The main substrates in apple peel are flavan-3-ols and flavonols (quercetin glycosides) and to a lesser extent derivatives of hydroxydnnamic acids are present (chlorogenic add and some other depsides). 

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