Flavonoid copigmentation

Among flavonoid interaction processes, copigmentation has been extensively studied for a review see Brouillard and Dangles (1993). 

Anthocyanins are grape-derived flavonoid compounds and are initially responsible for the color of red wine. The red appearance of anthocyanins in wine is dependent upon many factors including wine pH, ethanol concentration, copigmentation and anthocyanin substitution pattern. 

Anthocvanlns. Anthocyanlns are flavonoid, phenolic-based, water-soluble compounds located in the cell vacuole of the epidermal cells of many fruits and vegetables (371. They confer the characteristic red and blue colors of many flowers and fruits and as such are Important components of visual quality. The anthocyanins are pH indicators and are red at low pH, colorless at Intermediate pH and blue at higher pH. The blue colors at high pH are the result of copigmentation and metal chelation rather than a direct effect of pH. This can result in discoloration of fruits packed in metal containers or handled with metal implements (381. 

Flower pigments. Term for a subgroup of plant pigments responsible for the manifold colors of flowers. The most important F. p. are the anthocyanins, flav-onoids, carotinoids, and betalains. Yellow colors are caused by flavonoids, carotenoids, and betaxanthins while anthocyans and betacyans (see betalains) are responsible for red, violet, and blue colors. The many color tones result on the one hand from the simultaneous presence of flavonoids and anthocyans (intermo-lecular copigmentation) and on the other hand from intramolecular copigmentation and the formation of chelates between metal salts and anthocyans. 

Copigmentation is usually classified in (a) intermolecular anthocyanin-anthocyanin self-association, (b) intermolecular anthocyanin-copigment (i.e., flavonoids, phenolic acids) association, (c) intermolecular anthocyanin-copigment-metal ion association or (d) intramolecular self-association of acylated anthocyanins. 

Fig. 57.12 Schematic representation of the intermolecular copigmentation between anthocyanins and flavonoids. (—), anthocyanin (—), flavonoids [170]...

In processed fruit and vegetables, the situation is more complex. Anthocyanins in plants (pH of from 2.5 to 7.5) occur as a purplish-red neutral quinoid base, but in food products they may be in media of different pH. However, they are mostly stabilised by inter co-pigmentation (interactions with other flavonoids) or intra copigmentation (acylated forms), or by interactions with other food components. Many products therefore retain their original colour... 

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