Postharvest Biology and Technology of Fruits, Vegetables, and Flowers

268 POSTHARVEST BIOLOGY & TECHNOLOGY OF FRUITS, VEGETABLES, & FLOWERS
OH
HO
OH
OH
OH O
Naringenin chalcone
CHI
OH
HO
O
FNS1
HO
O
FNSI1
OH O
Flavone
OH O
Flavanone
OH
OH
F3H
OH
HO
O
FLS
HO
O
HO
OH
Flavonol
OH
O
O
OH
OH
OH
OH
FDR
HO
OH
O
Dihydroflavonol
OH
O
OH
Flavan-3-ol
Flavan-3,4-cis-diol Anthocyanidin
(leucoanthocyanidin)
Fig. 12.4 Biosynthesis of major fruit flavonoids, flavanone, flavone, flavonol, flavan-3-ol, and anthocyanidin.
Enzymes as follows: CHI, chalcone isomerase; F3H, flavanone 3-hydroxylase; DFR, dihydroflavonol 4-reductase;
FNS, flavone synthase; FLS, flavonol synthase; ANS, anthocyanidin synthase; FDR, flavan-3,4-cis–diol reductase.
OH
DFR
OH
OH
ANS
HO
OH
O +
OH
OH
nicotinamide adenine dinucleotide phosphate (NADPH)-dependent dihydroflavonol 4-
reductase (DFR). Anthocyanindin biosynthesis from flavan-3,4-cis-diol is catalyzed by
anthocyanidin synthase (ANS). The key step of formation of flavan-3-ols from flavan-3,4-
cis-diol is catalyzed by NADPH-dependent flavan-3,4-cis-diol reductase. Except flavan-3-
ols, flavonoids usually occur in fruits as glycosides.
12.6 Regulation of flavonoid synthesis during ripening
and storage
Red pigmentation in apple fruit is due to a unique anthocyanin, cyanidin-3-O-galactoside,
which serves as an indicator of fruit maturity or ripeness for the apple producer and consumer
(Fig. 12.5). Flavonoid biosynthesis, including the anthocyanins, is regulated in part by the