Anthocyanins reactions during

Precursors. Precursors for this reaction are compounds exhibiting keto-enol tau-tomerism. These compounds are usually secondary metabolites derived from the glycolysis cycle of yeast metabolism during fermentation. Pyruvic acid is one of the main precursor compounds involved in this type of reaction. During yeast fermentation it is decarboxylated to acetaldehyde and then reduced to ethanol. Acetone, ace-toin (3-hydroxybutan-2-one), oxalacetic acid, acetoacetic acid and diacetyl, among others, are also secondary metabolites likely to participate in this kind of condensation reaction with anthocyanins. 

The above-mentioned release of hydroxycinnamic acids from anthocyanin esters during wine maturation may be only due to chemical reactions but conversions of acid precursors to volatile phenols are typically dependent on enzyme or microbial activity. 

Anthocyanins were decolorized at pH 3.0 by the addition of sodinm sulfite at the C-2 or C-4 of the chromophore, a reaction that was rapidly reversible on acidification. Snlfnr dioxide, EDTA, and a combination of snlfnr dioxide and EDTA exerted very small effects on the losses of anthocyanins in strawberry pnrees and juices during 10 wk of storage at -20°C. Conversely, the addition of snlfnr dioxide and storage at 20°C slowed the anthocyanin losses and concnrrently decreased the formation of polymeric componnds, especially in pnrees. EDTA had a slight effect on color stability. ... 

Studies of the stability and stabilization of anthocyanins are still required, based on the extreme importance of those pigments for food colors. Modem HPLC-MS equipment also allows us to easily follow the copigmentation reactions in detail, calculate their kinetic and thermodynamic parameters, identify the products formed during the reactions, and thus shed new light on the stability and stabilization of these pigments. Since anthocyanins play important roles as natural colorants for... 

As a first approximation, this experiment represents the evolution of the coloring matter in red wines during aging. It confirms the large role of tannins in the color of old wines and thus shows that tannins play an important part in the color of young wines. Taken as another point, the possibility of a reaction between the anthocyanins and tannins already postulated (50) is accurately described. 

During the weeks that follow vinification several things happen simultaneously (a) The reduced anthocyanins are reoxidized, producing a color increase (b) The anthocyanins, in reduced or oxidized form, are partially destroyed by various chemical reactions or by condensation with tannins. One may thus explain why, during that period the color of some wines increases while that of others decreases, depending on the relative rates of the two reactions occurring at this time. 

The phenolic compounds extracted from the fruit contribute to the development and stability of the wine s red color. The color evolution during vinification and aging is mainly due to chemical transformations to the phenolic compound derived from the fruit. Anthocyanins, responsible for the purple-red color of young wines, participate in reactions with other phenolic compounds to generate other, more chemically stable molecules. These changes involve oxidation, polymerization, and other... 

Traditionally, large oak barrels are used to facilitate the diffusion of oxygen. This is assumed to play a major role in the many chemical reactions occurring during aging. Oxidation reactions promote desired changes in wine phenolics (e.g., anthocyanins, flavonoids, and tartaric esters of hydrocinnamic acids) as well as oak phenolics extracted from the... 

A.2 Chemical Reactions of Anthocyanins During Winemaking Main Anthocyanin-... 

Fig. 9A.3 Main chemical reactions of anthocyanins during winemaking...

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