Grape phenolics: The anthocyanins of Vitis vinifera, variety shiraz

Abstract

The pigments of the Shiraz variety of Vitis vinifera grown in the Barossa Valley of South Australia have been identified as the 3‐monoglucosides of delphinidin, petunidin, malvidin and peonidin, together with a number of acylated derivatives of these anthocyanins. involving both p‐coumaric and caffeic acids. The principal acyl derivatives are two different p‐coumaroyl and one caffeoyl derivative of malvidin 3‐glucoside, and a p‐coumaroyl derivative of peonidin 3‐glucoside. Corresponding derivatives of the two other 3‐glucosides are present in small amounts. The point of attachment of the acyl substituent in the main group of p‐coumaroyl derivatives has been shown to be on the glucose moiety. The major pigment component is malvidin 3‐glucoside which in the various forms present is responsible for approximately 70% of the total colour. Crystalline samples of several of the components have been isolated and their extinction values determined.

Analysis of Anthocyanins

“…e. Thin-Laye r Chromatograph y (TLC). Somers (1966) and Conradie and Neethling (1968) used TL C for separation of grape pigments, as did Morto n (1967) for black currants. (Harborne, 1973).…”

The Anthocyanins of Grapes and Wines

“…But Somers (1966) has shown that the grape anthocyanins initiall y responsibl e for wine color are displaced, progressivel y and irreversibl y durin g aging, by more stable polymeric pigments which account for up to 50% of the color density withi n the first year. But Somers (1966) has shown that the grape anthocyanins initiall y responsibl e for wine color are displaced, progressivel y and irreversibl y durin g aging, by more stable polymeric pigments which account for up to 50% of the color density withi n the first year.…”

“…These new pigment forms are much less sensitive to change s in pH than are the free anthocyanins and are also quite resistant to decolorization by sulphur dioxide. The separation between free anthocyanins and polymeric pigments in wine is made by gel filtration on Sephade x G25 (Somers , 1966). Table VII I shows the effect of pH on the ionization (which determines the color intensity) and the X max of the anthocyanins of grapes and the polymeric pigments of wine.…”

“…Thi s fundamental fact was brought to evidence by Somers (1966Somers ( , 1971. They are dependen t upon the level of oxidation of the wine.…”

Quantitative Methods for Anthocyanins.

“…- Somers (1966) found that malvidin-&glucoside and the acylated pigments were only partially precipitated from grapes by neutral lead acetate and peonidin-3-glucoside not at all. Some loss of the more labile acylated pigments occurred when the precipitation was carried out with basic lead acetate (Somers, 1966) or in a slightly basic media (Ribkreau-Gayon, 1959).…”