Flavanol glucosides

Friedrich, W. and Galensa, R., Identification of a new flavanol glucoside from barley (Hordeum vulgare L.) and malt, Eur. Food Res. Technol, 214, 388, 2002. 

Otsuka, H. et al., Glochiflavanosides A-D flavanol glucosides from the leaves of Glochidion zeylanicum (Gaertn) A. fuss, Chem. Pharm. Bull, 49, 921, 2001. 

Nonaka G, Ezaki E, Hayashi K, Nishioka 1 1983 Flavanol glucosides from rhubarb and Rhaphio-lepis umbellata. Phytochemistry 22 1659-1661... 

After longer incubation times, the chromatographic profiles of solutions containing flavanol monomers, malvidin 3-glucoside, and acetaldehyde became more complex and... 

Laurie, V. F. and Waterhouse, A. L. (2006a). Glyceraldehyde bridging between flavanols and malvidin-3-glucoside in model solutions. /. Agric. Food Ghent. 54, 9105-9111. 

Two catechins, ( + )catechin and ( — )epicatechin, and two leucoanthocyanins were isolated from Bartlett pears by Nortje (165).. Durkee et al. (166) identified arbutin (p-hydroxphenyl-/ -D-glucoside) in mature and immature pears. Several flavanol glycosides such as quercetin 3-glucoside, isorhamnetin-3-glucoside, isorhamnetin-3-rutinoside, isorham-netin-3-galactoside, and quercetin-7-xyloside were identified by Duggan (167). 

Quercetryl-2"-acetate (= Quercetin 3-0-Rha-2"-acetate)] (flavonol O-glycoside) Quercimeritrin (= Quercetin 7-0-Glc) (flavanol O-glucoside) Reynoutrin (= Quercetin 3-0-Xyl) (flavanol glycoside)... 

Colored adducts in which the anthocyanin and the flavanol are linked by a carboxy-methine bridge, have also been identified, in addition to colorless carboxy-methine-linked catechin dimers (Chapter 9B), in model solutions containing (-i-)-catechin, malvidin-3-glucoside and glyoxylic acid (Es-Safi et al. 2003). 

Havonoid autoxidation in wine is a slow process but its rate increases with pH. For instance, products arising from addition of malvidin 3-glucoside onto epicate-chin quinone were observed only at pH 4 and above (Duenas et al. 2006a). Oxidation of flavanols and formation of B-type and A-type dehydrodicatechins was observed in the wine pH range (Oszmianski et al. 1996). When catalysts such as metal ions are present, oxidation of tartaric acid and subsequent formation of xanthylium pigments compete with autoxidation reactions. 

Sun, B., Reis Santos, C.R, Leandro, M.C., De Freitas, V., and Spranger, M.I. (2007). Fligh-performance liquid chromatography/electrospray ionization mass spectrometric characterization of new product formed by the reaction between flavanols and malvidin 3-glucoside in the presence of acetaldehyde, Rapid Comm. Mass Spectrom., 21, 2227-2236. 

More complex structures consisting of both malvidin 3-glucoside and flavanol units connected by different types of linkages, including direct, ethyl and A-type bonds have been partially characterized by mass spectrometiy in model solutions (72). Additionally, some of these compounds also contain pyranoanthocyanin moiety. 

The reaction mechanism proposed by Timberlake and Bridle (1976), suggests that acetaldehyde, in the form of a carbo-cation, reacts with flavanol (tarmin) at position C-6 or C-8 (Figure 1 (1)). This, via several condensation reactions, gives rise to tannin-ethyl-anthocyanin derivatives (Figure 1 (2)) such as malvidin-3-glucoside-ethyl-(epi)catechin and malvidin-3-(6-/7-coumaroyl)-glucoside-ethyl-(epi)catechin. 

The presence of the dimers malvidin-3-glucoside-ethyl-catechin (m/z 809, [M]" and malvidin-3-(6-p-coumaroyl)-glucoside-ethyl-catechin (m/z 955, [M] ) has been confirmed in wine and wine fractions with the help of ESI-MS. Other pigments (see below), in which the anthocyanin is joined to a flavanol via a vinyl fragment, can also be produced in the presence of acetaldehyde. 

Adducts of malvidin-3-glucoside with vinylcatechin, vinylepicatechin or vinyidiepicatechin (procyanidin B2), reported in model solutions containing malvidin-3-glucoside, acetaldehyde and the respective flavan-3-ol (Francia-Aricha et al., 1997) (Fig. 3, (b)), have also been detected in wine fractions (Mateus et al., 2002a, b Atanasova et al., 2002). In the latter work, the authors showed, via thiolysis, diat both proanthocyanidins and monomeric flavanols are involved in the formation of anthocyanin-vinylflavanol and anthocyanin-ediyl-flavanol pigments induced by acetaldehyde. 

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