Postharvest Biology and Technology of Fruits, Vegetables, and Flowers

186 POSTHARVEST BIOLOGY & TECHNOLOGY OF FRUITS, VEGETABLES, & FLOWERS
de novo synthesis, and it contributed to a delay of the cell wall degradation and prevented
softening.
Irradiation induces softening in mature green and pink tomato fruits within hours following
irradiation, and differences between irradiated and control fruit persisted throughout
postirradiation storage. Fruit irradiated at the mature green stage softened during postirradiation
storage but exhibited an apparently irreversible suppression in PG activity, with levels
remaining ≤10% of those of nonirradiated fruit. PG activity was less strongly affected in
irradiated pink fruit than in mature green fruit, but activity remained reduced relative to the
controls. PME and β-galactosidase activities were significantly enhanced in irradiated fruit
of both ripening stages in the early period following irradiation, but reductions were noted
after prolonged storage (Elassi et al., 1997).
The firmness of irradiated papaya fruits (500 Gy) was retained at least 2 days longer
than in control fruits and also had a slower rate of softening. The activity patterns of PG,
PME, and β-galactosidase were related to pulp softening and were affected by irradiation.
Irradiation may not have any direct effect on firmness, but it acted by altering the ripeninginduced
synthesis of cell wall enzymes, mainly PME (D’Innocenzo and Lajolo, 2001).
Fruit treated with UV-C remained firmer and softened more slowly than the control and
those treated with longer durations of exposure (Gonzalez-Aguilar et al., 2004). Exposing
packaged watermelons cubes to UV-C not only causes reduction in microbial populations
but also extends products shelf life without affecting juice leakage and overall visual quality
(Fonseca and Rushing, 2006).
Prestorage exposure of peaches with UV-C irradiation significantly reduced chilling
injury. A higher accumulation of spermidine and spermine was found in peaches after
UV exposure, and it is postulated that these higher levels of polyamines apparently are a
response to the UV-C irradiation and might be beneficial in increasing the resistance of fruit
tissue to deterioration and chilling injury (Gonzalez-Aguilar et al., 2004).
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