Glucosides onion

Four cyanidins with 4 -glucosidation were recently isolated in minor amounts from pigmented scales of red onion. Two were the only anthocyanins with B ring sugar substitutions and no glycosyl moieties in anthocyanidin position 3, whereas the other two were also glycosilated at the usual position 3. ... 

Fossen, T., Slimestad, R., and Andersen, 0.M., Anthocyanins with 4 -glucosidation from red onion. Allium cepa. Phytochemistry, 64, 1367, 2003. 

Aziz AA, Edwards CA, Lean ME and Crozier A. 1998. Absorption and excretion of conjugated flavonols, including quercetin-4 -0-(3-glucoside and isorhamnetin-4 -O-(i-gIu coside by human volunteers after the consumption of onions. Free Radic Res 29 257-269. 

Price, K.R., Bacon, J.R., and Rhodes, M.J.C., Effect of storage and domestic processing on the content and composition of flavonol glucosides in onion Allium cepd), J. Agric. Food Chem., 45, 938, 1997. 

Two classes of dimeric anthocyanins isolated from plants (section 10.2.6) have been identified in plants for the first time. One class includes pigments where an anthocyanin and a flavone or flavonol are linked to each end of a dicarboxylic acyl unit. The other class includes four different catechins linked covalently to pelargonidin 3-glucoside. During the last decade, seven new desoxyanthocyanidins and a novel type of anthocyanidin called P)Tanoanthocyanidins have been reported (Section 10.2.2). Toward the end of the 20th century, several color-stable 4-substituted anthocyanins, pyranoanthocyanins, were discovered in small amounts in red wine and grape pomace.Recently, similar compounds have been isolated from extracts of petals of Rosa hybrida cv. M me Violet, scales of red onion, and strawberries. About 94% of the new anthocyanins in the period of this review are based on only six anthocyanidins (Table 10.2). 

Four cyanidin 4 -glucosides have recently been isolated from pigmented scales of red onion. These structures were established by extensive use of 2D NMR spectroscopy and electrospray LC MS. The previous report on 4 -glucosyl linkages in two anthocyanins from... 

Glycosides of flavonols from onions, such as quercetin-4 -0-glucoside and quercetin-3 -0-methyl-4 -0-glucoside, have been found in the plasma of volunteers with a peak of absorption of 0.5 - 4 h [64]. 

The bioavailibility of quercetin-glycosides from onions, containing mainly quercetin-p-glucosides, was superior to that of various quercetin glycosides from apples (containing a mixture of quercetin-(3-galactosides and P-xylosides) and of pure quercetin-3-mtinoside (major species in tea). The possible matrix effect of the foods remains unclear. 

Flavonols that accumulate in plant tissues are almost always in the form of glycosylated conjugates. The main flavonols in onions are quercetin- 4 -O-glucoside and quercetin-3,4 -0-,diglucoside with smaller amounts of isorham-netin-4 -0-glucoside (Fig. 1.3) [Mullen et al., 2004]. 

Cyanidin-3-0-(6"-0-malonyl)laminaribioside Cyanidin-3-0-(6"-0-malonyl)glucoside Figure 1.23 Main anthocyanins in red onions. 

Das demonstrated that oral administration of labeled 3-0-methylcatechin to three volunteers was followed by plasma peak levels within 2 hours after administration [69]. Hollman et al. studied the absorption of different glycosides of quercetin and the quercetin aglycone in nine healthy ileostomy subjects to avoid losses caused by colonic bacteria [30-31]. The absorption after oral administration decreased in the following order 52% for quercetin glucosides from fried onions > 24% for quercetin aglycone > 17% for quercetin nitinoside [31]. Consequently, humans absorb considerable amounts of quercetin, but the absorption depends on the glycosidic nature of the flavonoid [31]. 

Of the three isomers, catechol is the only member to occur naturally, namely in the leaves and branches of the oak and willow, in apples, onions, and crude sugar beet and in the tannin layer of mycorrhizas (ref.28). Its derivatives are widely distributed in higher plants. Hydroquinone occurs as the glucoside arbutin (4-hydroxyphenyl-D-glucopyranose) and resorcinol only in pyrolysis products in, for example, cigarette smoke. 

It has been reported that the epidermis of onion scales contains only glucosides of quercetin, while the dry outer skin contains quercetin mainly in its free state [73]. Quercetin 4 -glucoside and other diglucosides are... 

Fig. (10). HPLC chromatogram of red onion anthocyanins and other phenols (1) quercetin 3,4 -diglucoside, (2) quercetin 4 -glucoside, (3) isorhamnetin 4 -glucoside, (4) cyanidin 3-glucoside, (5) cyanidin 3-arabinoside, (6) cyanidin 3-malonylglucoside, and (7) cyanidin 3-malonylarabinoside. HPLC conditions RP Cig column (12 x 0.4 cm particle size 5 im). Mobile phase acidified water (5% formic acid) (A) and methanol (B). Gradient 0 min- 15% B, 15 min- 35% B, 25 min- 40% B. Flow rate 1 mL/min.

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