Anthocyanins in grape skins

Vidal, S. et al.. Mass spectrometric evidence for the existence of oligomeric anthocyanins in grape skins, J. Agric. Food Chem., 52, 7144, 2004. 

Vivas, N.G., Nonier, M.-F, Guerra, C., Vivas, N. (2001). Anthocyanin in grape skins during maturation of Vitis vinifera L. cv. Caberent Sauvignon and Merlot Noir from different bordeaux terroirs. J. Int. Sci. Vigne Vin35, 149-156. 

Table 2.4 HPLC gradient program used for analysis of anthocyanins in grape skins extract by C18 (250 x 4mm, 5 pm) column (chromatogram in Figure 2.14) (flow rate 0.5mL/min).

Bakker, J., Timberlake, C.F., The distribution of anthocyanins in grape skin extracts of Port wine cultivars as determined by high performance liquid chromatography, J. Sci. Food Ague., 1985, 36, 1315-1324. 

Revilla, 1. et al.. Identification of anthocyanin derivatives in grape skin extracts and red wines by liquid chromatography with diode array and mass spectrometric detection, J. Chromatogr. A, 847, 83, 1999. 

Several oligomeric anthocyanins and Mv-4-vinyl-polycatechins were identified in grape skin extracts (Table 3.11) (Asenstorfer et al., 2001 Vidal et al., 2004). An example of identification of two dimeric anthocyanins by direct infusion ESI-MS/MS analysis is reported in Figure 3.18. 

Figure 3.18 Direct-infusion ESI-MS/MS product ion spectra of anthocyanin dimers composed of Mv-glucoside with (A) Mv-3-glucoside (m/z 985, MvMv + 2G) and (B) Pn-3-glucoside (m/z 955, MvPn+2G) identified in grape skin (ESI needle, orifice, and ring potentials at 5000, 150, and 250V, respectively collision gas N2 collision energy 30-60 V). (Reproduced from J. Agric. Food Chem., 2004, 52, 7144—7151, Vidal et al., with permission of American Chemical Society)...

Although a high concentration of anthocyanins in the skins is necessary to obtain a deep-colored wine, it is not the only condition. The cells must also be sufficiently decayed to make these molecules easily extractable by non-aggressive technology. At phenolic maturity, grapes have both... 

Rich sources of anthocyanins are grape skins and bilberries (Vaccinium myrtillus)—along with other members of the Vaccinium genus including blueberries. Bilberry has long been associated with effects on microcirculation and is used in diabetic neuropathy and... 

Anthocyanin may also dimerize yielding A-A dimers. Such dimers were tentatively identified by ESI-MS in grape skin extracts (Vidal et al, 2004), as well as in red wine fractions obtained by high-speed countercurrent chromatography (Salas et al, 2005) and by fractionation on Toyopearl after bisulfite bleaching (Alcalde-Eon et al, 2007). Two structures have been proposed for A-A+ A-type bond (C4-C8 and C2-0-C7) flavan-fiavylium dimers and B-type bond (C4-C8) flavene-flavylium (Vidal et al, 2004). Oligomers consisting of a flavanol residue directly linked to an anthocyanin dimer (F-A-A" ) have also been recently identified in red wine fractions (Alcalde-Eon et al., 2007). 

The most common supercritical medium is CO2 because of its low critical temperature (31°C) and critical pressure (7.3 MPa), its cost effectiveness, its food grade status, and overall environmental friendliness. However, due to its low polarity, supercritical CO2 (SC-CO2) alone did not perform well in the extraction of phenolic compounds and anthocyanins from grape skins (Mantell et al. 2003 Vatai et al. 2009). A cosolvent, usually ethanol, can be added to SC-CO2 during extraction to enhance polarity. Such a mixture can result in a two-fold increase in phenols and three-fold increase in anthocyanins extracted. Isolation of quercetin might also be improved as SC-CO2 can remove the nonpolar components, thus concentrating the quercetin in the feed material. Water and methanol can also be added as cosolvents to increase the polarity of SC-CO2. 

Ju and Howard (2003) studied pressurized hquid extraction of anthocyanins from dried red grape skins with six solvents at temperatures ranging from 20 to 140°C using 10.1 MPa. They found that the type of solvent and the temperature used affected the types and levels of anthocyanins in the PLE extracts. 

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