Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Chemical transformations of flavonoids

Anthocyanins are highly reactive in aqueous medium and can undergo a nucleophilic attack on the electron-deficient carbons 2 and 4 of the pyranic ring or an electrophilic attack on the carbons 6 and 8 of the phloroglucinol A-ring, probably in the noncharged hemiacetal and quinonoidal forms (see Fig. 3.3). The hydroxyl groups may also react with electrophilic species. [Pg.63]

One of the most characteristic reactions that evidence the electrophilic character of the pyranic ring C is its discoloration by SO2 in aqueous solvents. This results from the nucleophilic attack of the anion hydrogen bisulfite on carbon 4 and, to a less extent, on carbon 2 to give rise to a colorless adduct (Berke et al, 1998). This explains the decrease in the color intensity of the must or wine during wine-making immediately after sulfitation. However, this reaction is reversible and as the SO2 (a gas) is evaporated (HSO3- (aq.) S02(g) + H2O) or reacts with other wine constituents such as aldehydes, the equilibrium is displaced to the formation of flavylium, the colored form of anthocy-anin, and musts or wines recover their original color. [Pg.63]

Over the past decades, several groups of compoimds resulting from anthocyanin transformations have been identified in wines (summarized in Fig. 3.4). In general, these [Pg.63]


See other pages where Chemical transformations of flavonoids is mentioned: [Pg.63]    [Pg.67]   


SEARCH



Chemical transformation

Of flavonoids

© 2024 chempedia.info