Phenolic substances of grapes and wine

V. L. Singleton and P. Esau, Phenolic Substances of Grapes and Wine, and Their Significance, Adv. Food Res., Suppl. 1, (1969). 

Studies have shown that many phenolic substances of grapes and wine may possess some antibacterial properties (146, 147, 148). For an extensive review and discussion pertaining to the bactericidal effect of grape and wine phenolics, see Ref. 122. 

Analytical Fractionation of the Phenolic Substances of Grapes and Wine and Some Practical Uses of Such Analyses... 

Singleton, V.L. 1974, Analytical fractionation of the phenolic substances of grapes and wine and some practical uses of such analyses. In Chemistry of Winemaking (A.D. Webb, ed.) pp. 184-211. American Chemical Society, Washington, D.C. 

SEC of grape and wine proteins has to be performed on samples deprived of phenolics because these compounds tend to bind irreversibly the stationary phase. Phenolic compounds are removed by passing the protein extract through a C18 cartridge (see above). As an alternative to removing the interfering substances, it is also possible to pre-treat the sample with small amounts of the same stationary phase used for SEC. 

Similarly to pectic substances, the direct organoleptic role of mannoproteins on the impression of body and softness in wine is certainly negligible. Mannoproteins may, however, have an indirect effect on astringency when they combine with phenolic compounds from grapes or oak (Section... 

Phenolic substances in red wine were shown to inhibit LDL oxidation in vitro [95]. In previous studies, red wine-derived phenolic acids [115,116], resveratrol [117], flavonols (quercetin, myricetin) [68,118,119], catechins [66,120], and the grape extract itself [121,122] have been shown to possess antioxidant properties. The finding that ethanol and wine stripped of phenols did not affect LDL oxidation further confirmed that the active antioxidant components in red wine are phenolic compounds [123]. Red wine fractionation revealed major antioxidative potency to monomeric catechins, procyanidins, monomeric anthocyanidins, and phenolic acids [123]. The flavonol quercetin and the flavonol catechin were both tested for antioxidative and antiatherogenic effects in the atherosclerotic E° mice [111]. E° mice at the age of 4 weeks were supplemented for up to 6 weeks in their drinking water with placebo (1.1% alcohol) or with catechin or quercetin (50 pg/day/mouse). The atherosclerotic lesion area was smaller by 39% or by 46%, respectively, in the treated mice than in E° mice that were treated with placebo (Fig. 4A-E). 

Consequently, the definition of maturity varies, depending on the objective. For example, the production of dry white wines requires grapes whose aromatic substances are at a maximal concentration and whose acidity is still sufficient. In certain situations, an early harvest can be interesting. Conversely, when the elaboration of a quality red wine is desired, grape development must be left to continue to obtain the most easily extractable phenolic compounds. 

Wine contains many phenolic substances. The phenolics have a number of important functions. In wine, especially in red wines, affect the tastes of bitterness and astringency. Second, the coior of red wine is caused by phenoiics. They are also bactericidal agents and impart antioxidant properties, being especially found in the skin and seeds of the grapes. 

Procyanidins seem to represent the second most abundant natural phenolic after lignin and, with other substances, they might be responsible for the oral sensation of astringency in ripening fruits (apples, peaches, grapes, berries), beverages (tea, wine), cocoa and chocolate [7, 8]. 

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