Anthocyanins malvidin-3-glucoside

The products of condensation between anthocyanins and 4-vinylphenol, first detected and isolated from polymer membranes used in the microfiltration of red wine (Cameira dos Santos et al, 1996), have been studied by UV-visible, mass, and H" NMR spectrometry. This has confirmed the presence of adducts formed between the most abundant anthocyanins (malvidin-3-glucoside and malvidin-3-(6-/7-coumaroyl)-glucoside) and 4-vinylphenol (Fulcrand et al., 1996). The proposed structures are shown in Fig 3 (a). 

The fruits contain resveratrol and at least 14 different anthocyanins (malvidin-3-arabi-noside, cyanidin-3-xyloside, cyanidin-3-ruti-noside, peonidin-3-glucoside, petunidin-... 

The degradation kinetics of malvidin 3-glucoside in ethanolic solutions under conditions simulating wine accelerated with the increase of ethanol concentration, probably because the extent of anthocyanin self-association decreased with elevated ethanol concentration. ... 

The synthesis of two new red wine pigments by nucleophilic addition of vinylphenols to malvidin 3-glucoside has been described. The structures of the two new pigments and their formation are shown in Fig. 2.105. HPLC-DAD and HPLCMS confirmed the occurrence of these two anthocyanin derivatives in red wine [239],... 

Fig. 4.2 HPLC-DAD chromatograms of anthocyanins from soluble and insoluble extracts of black, red-brown, and brown soybean seed coats at 520 nm. (a, d) Black (Clark), (b, e) red-brown (Mil), and (c, f) brown (MlOO) seed coats, (a and b) Pulverized fresh seed coats extracted with 80% methanol in water, (d-f) Insoluble pulverized seed coat fraction extracted with 1-butanol/HCl (19 1) 1% SDS. Compound identifications were based on comparison of retention times and absorption spectra to authentic standards. Peak 1, unknown peak 2, delphinidin-3-O-galactoside peak 3, delphinidin-3-O-glucoside peak 4, cyanidin-3-O-galactoside peak 5, cyanidin-3-O-glucoside peak 6, petunidin-3-O-glucoside peak 7, pelargonidin-3-O-glucoside peak 8, peonidin-3-O-glucoside and peak 9, malvidin-3-O-glucoside...

Anthocyanins are usually represented as the red flavylium cations (Figure 5.1, left). However, this form is predominant only in very acidic solvents (pH < 2) such as those used for HPLC analysis. In mildly acidic media, the flavylium cations undergo proton transfer and hydration reactions, respectively, generating the quinonoidal base and the hemiketal syn carbinol) form (Figure 5.1, right) that can tautomerize to the chalcone. Thus, at wine pH, malvidin 3-glucoside occurs mostly as the colorless hemiketal (75%), the red flavylium cation, yellow chalcone, and blue quinonoidal base being only minor species. 

Spectrophotometric studies were conducted from pH 0.1 to 5.7. The thermodynamic constants calculated, assuming that the absorbance of AH+-AH+ was twice that of AH -AOH and that the second hydration constant (pAhi) was equal to the proton transfer constant (pA, were 1.8 (pAhi) for the first hydration reaction and 4.6 (pAThi pA) for the second, whereas the hydration and proton transfer constants calculated for malvidin 3-glucoside are 2.6 and 4.25, respectively. Based on these hydration constants, the only significant form of the methylmethine dimer at wine pH is AH+-AOH, in which one of the anthocyanin moieties is under the red flavylium form and the other one is hydrated, as predicted from mass spectrometry data. Thus, conversion of grape anthocyanins (75 to 80% colorless AOH, 20 to 25% red AH+ in wine pH range) to the methylmethine bis-anthocyanin (50% AOH, 50% AH ) may be responsible not only for a shift toward a more purple tint but also for a twofold increase in color intensity. 

Brouillard, R. and Delaporte, B., Chemistry of anthocyanin pigments. 2. Kinetic and thermodynamic study of proton transfer, hydration, and tautomeric reactions of malvidin 3-glucoside. J. Am. Chem. Soc. 99, 8461, 1977. 

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