花青素形式與pH的相關變化

In an aqueous medium, including foods, anthocyanins can exist in four possible structural forms depending on pH (Fig. 21, I): the blue quinonoidal base (A), the red flavylium cation (AH+), the colorless carbinol pseudobase (B), and the colorless chalcone (C). Shown in Figure 21 are the equilibrium distributions of these four forms in the pH range 0–6 for malvidin-3-glucoside (Fig. 21, II) dihydroxyflavylium chloride (Fig. 21,III) and 4 methoxy-4-methyl-7-hydroxyflavylium chloride (Fig. 21, IV). For each pigment only two of the four species are important over this pH range. In a solution of malvidin-3-glucoside at low pH the flavylium

(I) The four anthocyanin structures present in aqueous acidic solution at room

temperatures: A, quinonoidal base (blue); (AH +) flavylium salt (red); B, pseudobase or carbinol (colorless); C, chalcone (colorless). (II–IV) Equilibrium distribution at 25°C of AH +, A, B, and C as a function of pH: (II) for malvidin 3- g lucoside; (III) for 4',7-hydroxyflavylium chloride; (IV) for 4'-methoxyl-4-methyl-7-hydroxy flavylium chloride. (From Ref. 10.)