Changes in Nutritional Quality of Fruits and Vegetables During Storage - Postharvest Biology and Technology of Fruits, Vegetables, and Flowers - page 449

Phenylalanine

PA L

Cinnamic acid

C4H

p -Coumaric acid

4CL

Phenyl propanoid
pathway

p -Coumaryl CoA

CHS

Flavonoid pathway

Acetyl-CoA Malonyl-CoA

Chalcone

CHI

Flavanone (naringenin)

F3H

Dihydroflavonol

DFR

Leucoanthocyanidin

ANS

UFGT

Glycosylated
anthocyanindins

Anthocyanidin Anthocyanin

Petunidin Pelargonidin
Fig. 21.2 A simplified presentation of anthocyanin biosynthesis in plants. PAL, phenylalanine ammonia lyase;
C4H, cinnamate-4-hyroxylase; 4CL, 4-coumaryl CoA ligase; CHS, chalcone synthase; CHI, chalcone isomerase;
F3H, flavanone-3-hydroxylase; DFR, dihydroflavonol-4-reductase; ANS, anthocyanin synthase; UFGT, UDP-
glucose flavonoid 3-oxy-glucosyltransferase. (Adapted from Jaakola et al., 2002.)

Peonidin Malvidin Cyanindin Delphinidin

Anthocyanins are synthesized through flavonoid biosynthetic pathway, which is shown
in Fig. 21.2. The first step of anthocyanin biosynthesis is the condensation of three molecules
of malonyl-CoA with p -coumaroyl-CoA in the presence of the enzyme CHS, which
produces chalcone. In the presence of chalcone isomerase, chalcone is converted to fla-
vanone (naringenin) (Jaakola et al., 2002). Flavanone is hydroxylated through flavanone-
3-hydroxylase (F3H) and forms dihydroflavonols, which differ in the number of hydroxyl
groups. Dihydroflavonol-4-reductase (DFR) transforms dihydroflavonols to colorless leu-
coanthocyanidin, which yields colored anthocyanidins in the presence of the enzyme an-
thocyanin synthase (ANS). The glycosylation of anthocyanidins leads to the formation of
anthocyanins by the enzyme UDP-glucose flavonoid 3-oxy-glucosyltransferase (UFGT).