الفهرس 
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Abstract
Irradiation processing of food is widely used now in many countries worldwide as a safe, successful and valuable method for food preservation. The process decreases or eliminates foodbome pathogen thereby reducing foodbome illness; decreases or eliminates potential spoilage microorganisms thereby extending the shelf-life of perishable foods like meats, seafood, poultry, and fresh fruits. It can also be applied to prevent sprout inhibition of bulbs and tubers, insect disinfestation of grams and for microbial decontamination of spices and herbs.
Analytical detection of radiation treatment of food is very important means to implement such control, once the food items have left the irradiation facility. The presence of
reliable and sensitive detection methods to be applied on the food itself, is also very important in order to facilitate international trade in such foods, reforce consumer confidence
and check compliance with existing regulations. Ten international standards regarding different detection
procedures for irradiated foods have been adopted by the European Committee for Standardization (CEN) and are now
available to food control agencies.
Among the approved microbiological and biological detection methods are the DEFT/APC (EN 13783: 2001) and
the DNA comet assay (EN 13784:2001), which previously described as a rapid and inexpensive screening tests to identify radiation treatment of foods.
A number of researchers have suggested the use of the shift in microflora load (viable aerobic bacterial counts, Gram-
negative bacteria, Gram- positive bacteria, Enterobacteriaceae
group, molds and yeasts) as a simple method to give an indication whether an irradiation treatment has been applied.
In Egypt, there are very limited (if any) published papers dealing with the detection of irradiated foods on the
basis of microbiological and biological changes inducing by irradiation in the food itself. Therefore, the main aim of the present study is to use simple, rapid and inexpensive microbiological and biological methods for the detection or screening of gamma radiation treatment of some foods from
both plant and animal origin at Cairo markets.
The proposed methods in this work include the shift in microbial load, DEFT/APC and DNA comet assay. The selected foods were black pepper and strawberries (representing foods of plant origin) and fresh and frozen deboned chicken (representing foods of animal origin). The black pepper samples were purchased from local
market at Cairo. These were packed and irradiated at different gamma radiation doses (2.5, 5.0, 10.0 and 15.0 kGy).
Unirradiated and irradiated samples were stored at ambient temperature for 8 months and analyzed at zero time of storage and every two months upon storage. It was found that:
2- Irradiation greatly reduced or eliminated the viable
1- The characteristics of microbial population of irradiated black pepper samples have been changed.
microorganisms and the reduction was proportional to irradiation dose.
3- The very low count of total viable bacterial count around
3 loglO or less and the unpresence of mold and yeasts could be used as an indication for radiation treatment of
black pepper samples to level of at least 10 kGy or more.
4- The disappearance of Gram- negative bacterial throughout the storage period might also be used as an indication of radiation treatment of black pepper samples to level of at least 2.5 kGy.
5- The difference between DEFT count and APC count (DN)
of around 4 log., units or more could be used for screening radiation treatment of black pepper samples to level of at
least 10 kGy or higher up to 8 months of storage.
6- Photographs obtained by DNA comet assay showed that irradiation of black pepper samples at dose levels used
have caused damage to DNA (fragmentation) and the DNA
fragments stretched or migrated out of the cells towards the anode of agarose gel electrophoresis, appearing like
comet (head with tail). Moreover, the comet tails were proportional with irradiation dose and storage period.
7- Image analysis of DNA comet (the percentage of DNA in tail and the tail length) revealed that the values of % DNA in tail and the tail length of the irradiated samples increased with increasing radiation dose and storage
period.
8- The results of photographs and image analysis obtained by the DNA comet assay could successfully be used to detect radiation treatment, in particular at higher doses (5kGy or
more) of black pepper samples up to only 2 months.
The strawberry samples were purchased from local
market, packed and irradiated at different gamma radiation
doses (1, 2, 3 and 4 kGy). Unirradiated and irradiated samples
were stored at 4± 1 QC for 28 days and analyzed at zero time of
storage and every 7 days. It was found that:
2- Low viable counts of total aerobic bacterial count (210gIO
or less) in strawberry samples could be used as an
indication parameter of irradiation treatment with 4 kGy.
3- The disappearance of Gram-negative bacteria and
Enterobacteriaceae either immediately after irradiation or
during the storage period may be used as an indication of
radiation treatment of strawberry samples to level at least
1.0 kGy, while the count of molds and yeasts in the
samples (2.510gIO or less) could be used as an indication
for radiation treatment to level of at least 3kGy or more.
4- The DN value of around 310gIO units or more could be used
or screening radiation treatment of strawberry samples to
level of at least 4kGy up to 28 days of storage.
5-Photographs of DNA comet assay showed that irradiation
of strawberry samples caused damage to DNA (fragmentation) and the DNA fragments appear in the agarose gel as comet with tails and the comet tails were proportional with irradiation dose and storage period.
6- Image analysis of DNA comet showed that the values of% DNA in tail and the tail length of the irradiated samples
increased with increasing radiation dose and storage
period.
7- Photographic and image analysis indicated the applicability of the using DNA comet assay for detection
of irradiated strawberry samples up to 7 days of refrigerated storage.
Fresh-deboned chicken
The fresh-deboned chicken samples were purchased from local market, irradiated at different gamma radiation
doses (2, 3, 4 and 5 kGy). Unirradiated and irradiated samples were stored at 4± 1 QC for 28 days and analyzed at zero time of storage and every 7 days. It was found that:
1- The very low count of total viable bacterial count around
2.510glO or less as well as mold and yeasts counts around
2 log)o could be used as an indication for radiation treatment of deboned chicken samples to level of at least
4kGy or more.
2-The unpresence of Gram- negative bacteria and Enterobacteriaceae may be used as an indication of radiation treatment of deboned chicken samples to level of at least 2.0 kGy.
3- The difference between DEFT count and APe count (DN) of around 310gJO or more could be used for screening
radiation treatment of deboned chicken samples to level of at least 4kGy or higher up to 28 days of refrigerated
storage.
4-Photographs and image analysis of DNA comet assay
showed that irradiation of deboned chicken samples caused
damage to DNA (fragmentation). The DNA fragments appeared as comet with tail and the tail length and % DNA
in tail were proportional with irradiation dose and storage
period.
5- Based on DNA comet assay, the differentiation between
unirradiated and irradiated fresh deboned chicken samples
was possible up to only 7 days of refrigerated storage.
Frozen- deboned chicken
The frozen deboned chicken samples were purchased from local market, irradiated at different gamma radiation
doses (2, 4, 6 and 8 kGy). Unirradiated and irradiated samples
were stored at -1 O± 1 QC for 3 months and analyzed at zero time
of storage and every 1 month. It was found that:
1- The average count of viable aerobic bacteria of around
2.510glO or less and the disappearance of mold and yeasts may indicates that frozen- deboned chicken samples
could be irradiated at dose level of at least 6kGy or more.
2- The disappearance of Gram- negative bacteria and Enterobacteriaceae in these samples may be used as an
indication for irradiation treatment at level of at least 2 kGy.
3- The log DEFT/APC (DN) around 2.5 10glO units or more could be a criterion for radiation treatment of frozen- deboned chicken samples at dose level of at least 6kGy or
more up to 3 months of frozen storage.
4- Photographs and image analysis of DNA comet assay indicated the possible use of DNA comet assay for screening radiation treatment of frozen- deboned chicken up to only one month.