Biochemistry of Fruits - Postharvest Biology and Technology of Fruits, Vegetables, and Flowers - page 30

Photosynthesis

Glucose

UDP glucose
pyrophosphorylase

Glucose-1-phosphate
ATP

ADP glucose
pyrophosphorylase

UTP

PPi

ADP-glucose

PPi

UDP-glucose

Starch synthase
Branching
enzyme

-1-4-glucan
primer

α

Sucrose
phosphate
synthase

Fructose-6-
phosphate

(Amylose)

Starch

Amylopectin

Sucrose-6-phosphate

Phosphatase

α -Amylase Pi

β -Amylase
H 2 O

Starch
phosphorylase

Sucrose

Dextrins

Invertase

Maltose

α -Gluosidase

Sucrose
synthase

UDP

Glucose
+ fructose

Maltose

α -Gluosidase

Fructose

Glucose

α -Glucosidase

UDP-glucose

ATP
ADP

PPi

UTP

Hexokinase

UDP-glucose
pyrophosphorylase

Glucose-1-phosphate

Metabolic pool

Carbohydrate metabolism in fruits.

Fig. 3.3

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 starch-
degrading enzymes— -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

α -amylase, β -amylase, α