2009_Book_FoodChemistry

830 18 Fruits and Fruit Products
cyanidins. Increasing hydroxylation results in
a shift towards blue color (pelargonidin → cyanidin
→ delphinidin), whereas glycoside formation
and methylation results in a shift towards red
color (pelargonidin → pelargonidin-3-glucoside;
cyanidin → peonidin). The visual detection
threshold (VDT) is also influenced by the glycoside
residue, as shown by the following examples
(VDT in mg/l water): cyanidin-3-sophorosyl-
5-glucoside (3.6), cyanidin-3-glucoside (1.3),
cyanidin-3-xylosylgalactoside (0.9).
The color of an anthocyanin changes with the
pH of the medium (R = sugar moiety; cf. Formula
18.24).
Table 18.22. Anthocyanidins: absorption maxima in
the visible spectrum
Compound R 1 R 2 R 3 λ max (nm) a
(Formula 18.22)
R = H R = Glc b
Pelargonidin H OH H 520 506
Cyanidin OH OH H 535 c 525 c
Peonidin OCH 3 OH H 532 523
Delphinidin OH OH OH 544 c 535 c
Petunidin OCH 3 OH OH 543 c 535 c
Malvidin OCH 3 OH OCH 3 542 535
a In methanol with 0.01% HCl.
b 3-Glucoside.
c AlCl 3 shifts the absorption towards the blue region of
the spectrum by 14 to 23 nm.
Fig. 18.6. Absorption spectra of cyanidin-3-
rhamnoglucoside (16 mg/l) in aqueous buffered
solution at pH 0.71 (1), pH 2.53 (2), pH 3.31 (3),
pH 3.70 (4), and pH 4.02 (5). (According to Jurd, 1964)
(18.24)