Irradiation - Food Shelf Life Stability: Chemical, Biochemical, and Microbiological Changes - page 107

Immediately after irradiation, pectin in the 10 to 30% yellow papaya showed depo-
lymerization and demethoxylation. However, irradiation at doses from 0.5 to 1.0 kGy
of fruit at the 25 to 30% yellow ripeness stage had less depolymerization of pectin
and a firmer texture when ripe than the controls. Firmness of the irradiated fruit
lasted 2 days longer than the controls. Earlier work in the U.S. showed a consumer
preference for irradiated papaya. 202 The International Atomic Energy Agency has
recently published an excellent book on the use of irradiation as a quarantine method
for treatment of fruit such as mangos, papaya, and grapefruit in several countries. 203
Thomas 204 has reviewed possible applications of irradiation for the preservation of
subtropical fruits, citrus, grapes, and avocados. Miller and MacDonald 205,206 have
reported that the treatment of Florida grapefruit with irradiation at 0.3 kGy delayed
ripening and increased fruit firmness without damaging fruit quality. Mitchell et al. 207
reported that low dose irradiation of several Australian fruits, such as mango, lychee,
lemon, mandarin, nectarine, nectarine, peach, and persimmon, produced small
changes in soluble solids, pH, pulp color, vitamin C, organic acids, and sugars for
some of the fruits. However, the effects of storage were greater than the effects of
radiation. Similar effects were found in bananas, plantain, and nectarines by Cum-
mings. 190 Irradiation at doses from 50 to 250 Gy has been used to reduce post-harvest
losses in pineapple due to senescence and fungal diseases. 208 Jobin et al. 209 reported
on the effects of radiation combined with hot water on the physical, chemical, and
organoleptic properties of tangerines. They found that although radiation caused a
loss of firmness of the skin, the appearance, texture, flavor, pH, color, and soluble
solids content of the pulp was not affected by up to 14 days of storage. Earlier
O'Mahony 210 reported on the low post-harvest doses (0.6 to 0.8 kGy) treatment of
controlled atmosphere navel oranges and compared them to the controls for taste,
flavor, odor, firmness, peel and flesh color, peel blemishes, and ease of peeling. The
greatest differences were found in the degree of blemishing together with smaller
differences in flavor, odor, color, texture, and ease of peeling. Abbas 211 reported that
low dose (up to 50 Gy) irradiation could be used to delay the ripening of jujube
fruits with no significant loss in nutritional value. Irradiation alone or irradiation in
combination with hot water dip has been used to reduce post-harvest fungal rot in
table grapes. 212 Organoleptic quality, fruit firmness, and soluble solids content were
not affected, but decreases in acidity and ascorbic acid were reported. McLaughlin
et al. 213 reported that gamma irradiation of lychee at 75 or 300 kGy may be used
for disinfestation purposes with no adverse effects on fruit quality.
Thomas 214 has reviewed the applications of irradiation in controlling post-harvest
losses due to fungal decay, senescence and physiological storage disorders in tem-
perate fruits such as apples, pears, peaches, nectarines, plums, and berries. Unfor-
tunately for most fruits the irradiation dosage required to inhibit or destroy storage
rots and catabolic enzymes is more than enough to cause serious injury to the plant
tissue ( Table 3.5 ). 215
The application of gamma irradiation for improving the storage of climacteric
fruits like apples and pears has been extensively studied with respect to the control
of physiological disorders and reduction of decay caused by fungal pathogens. As
the results appear to be contradictory, later workers have turned to UV radiation.