Postharvest Biology and Technology of Fruits, Vegetables, and Flowers

30 POSTHARVEST BIOLOGY & TECHNOLOGY OF FRUITS, VEGETABLES, & FLOWERS
Photosynthesis
β-Amylase
Amylopectin
Glucose
Glucose-1-phosphate
ADP glucose
ATP
pyrophosphorylase PPi
ADP-glucose
Starch synthase
Branching
enzyme
Starch
α-Amylase
β-Amylase
H 2 O
Dextrins
Maltose
α-Gluosidase
Maltose
α-Gluosidase
α-Glucosidase
Glucose
Hexokinase
ATP
ADP
α-1-4-glucan
primer
UTP
Glucose-1-phosphate
(Amylose)
PPi
UTP
PPi
Sucrose-6-phosphate
Phosphatase
Starch
Pi
phosphorylase
Sucrose
Glucose
+ fructose
UDP glucose
pyrophosphorylase
Fructose-6-
phosphate
Invertase
UDP
UDP-glucose
UDP-glucose
UDP-glucose
pyrophosphorylase
Sucrose
phosphate
synthase
Sucrose
synthase
Fructose
Fig. 3.3
Metabolic pool
Carbohydrate metabolism in fruits.
Or, by the actions of sucrose synthase and UDP-glucose pyrophosphorylase, glucose-1-
phosphate can be regenerated from sucrose. As well, sugar alcohols such as sorbitol and
mannitol are major transport and storage components in apple and olive, respectively.
Biosynthesis and catabolism of starch has been extensively studied in banana, where
prior to ripening, it can account for 20–25% by fresh weight of the pulp tissue. All the starchdegrading
enzymes—α-amylase, β-amylase, α-glucosidase, and starch phosphorylase—
have been isolated from banana pulp. The activities of these enzymes increase during
ripening. Concomitant with the catabolism of starch, there is an accumulation of the sugars,
primarily, sucrose, glucose, and fructose. At the initiation of ripening, sucrose appears to
be the major sugar component, which declines during the advancement of ripening with
a simultaneous increase in glucose and fructose through the action of invertase (Beaudry
et al., 1989). Mango is another fruit that stores large amounts of starch. The starch is
degraded by the activities of amylases during the ripening process. In mango, glucose,
fructose, and sucrose are the major forms of simple sugars (Selvaraj et al., 1989). The sugar