Agriculture Reference
In-Depth Information
Antagonists
Disease (Pathogen)
Fruit crops
Candida oleophila
Penicillium rots (
Penicillium digitatum
and Penicillium italicum
), Crown rot (
Col-
letotrichum musae
), Anthracnose (
Colleto-
trichum gloeosporioides
)
Citrus, banana,
papaya
Debaryomyceshansenii
Green and blue mold (
Penicillium digita-
tum
and
Penicillium italicum
), Blue mold
(
Penicillium italicum
), Rhizopus rot (
Rhi-
zopus stolonifer
), Sour rot (
Geotrichum
candidum
)
Citrus, peach
16.12 IRRADIATION
Irradiation can be applied by exposing the fruit to ionizing radiations from
radioisotopes (normally in the form of gamma-rays but X-rays can also
be used) and from machines, which produce a high-energy electron beam.
The FDA has approved two types of radiation sources for the treatment of
foods: gamma rays produced by the natural decay of radioactive isotopes
of cobalt-60 or cesium-137, X-rays with a maximum energy of 5 million
electron volts (MeV), and electrons with a maximum energy of 10 MeV.
The rays are directed onto the fruit being irradiated, but the fruit itself nev-
er comes into contact with sources of radiation. Irradiation may be referred
to as a “cold pasteurization” process, as it does not significantly raise the
temperature of the treated fruits. Since fruits contain 80-95% water and
their intercellular spaces (about 20% of total volume) contain oxygen,
the high-energy gamma rays generate copious amounts of free radicals
from those of water and oxygen in the fruit immediately after radiation.
The free radicals in turn bring about the breakage of the genetic material
(DNA) of the insects and spoilage microorganisms, thus destroying them.
But after a short period (2-3 days) the free radicals get scavenged off or
converted into harmless molecules. Gamma radiation also delays ripen-
ing and senescence by decreasing the activity of the cell wall degrading
enzyme pectin methyl esterase (PME) and the activity of ACC-oxidase
involved in ethylene synthesis. Activities of some other enzymes likepoly-
galactosidase, cellulase and 1-aminocyclopropane-1-carboxylate oxidase
are also negatively affected. Ripening of bananas is inhibited at irradiation
doses of 0.25-0.35 kGy, and the irradiated fruit later can be ripened by
