Source of Article:http://www.separationsnow.com/coi/cda/detail.cda?id=19727&type=Feature&chId=3&page=1
Food irradiation is one of the
traditional ways to ensure the safety of many types of foods and protect
the consumer. It reduces or eliminates food-borne bacteria such as E.
coli, Salmonella and Campylobacter, controls pests
and parasites, and extends shelf life, while having virtually no effect on
the nutritional value of the food. The process has been endorsed by major
health organisations, including the WHO and the
US Centers for Disease Control and Prevention (CDC).
Initial fears that irradiation would produce dangerous
or radioactive substances in foods have been proven groundless. However,
irradiated foods still need to be stored and handled in the same way as
non-irradiated foods, using basic food safety rules to prevent subsequent
contamination by bacteria.
There are three main irradiation types, with gamma-irradiation
being the most common. Gamma rays from radioactive cobalt or caesium are directed at the food and can penetrate
several feet, so large quantities can be processed at once, like fruit in a
hopper. The newest technology, X-ray irradiation, can also penetrate longer
distances but electron beams only reach depths of about 3 cm in food.
Irradiation does have some positive side effects, such
as killing any living cells present. For instance, treatment prevents
potatoes from sprouting during storage. There are also some minor chemical
changes to the food, which have been put to good use. Minute amounts of
hydrocarbons and a group of compounds known as 2-alkylcyclobutanones (ACBs) are produced by the gamma-irradiation of
fatty-containing foods and they have become established marker compounds
for irradiation.
Two main types of hydrocarbons are formed by the radiolytic breakdown of triglycerides (TGs), the most common form of fat in foods. Their
compositions depend on that of the fatty acid groups in the TGs. Saturated alkanes with
one carbon atom less than the parent fatty acid, and alkenes with two
carbon atoms less than the parent and a new double bond at the C1 position
are produced.
The ACBs are formed from TGs by a cyclisation
reaction. The number of carbon atoms is the same as that of the parent
fatty acid, so determines the length of the alkyl chain as the ring size is
fixed. They are always detected in irradiated foods but never in
non-irradiated foods treated by other processes (freezing, microwaving, UV irradiation) so are ideal irradiation markers.
So, the presence of hydrocarbons and ACBs show that food has been irradiated, facilitating
compliance testing. But what happens to these compounds if the foods are
treated further after irradiation, say by roasting? Do they remain in the
food, are they removed, or are their levels changed?
For sesame seeds, this problem has been tackled by Joong-Ho Kwon and Jeongeun
Lee from the KyungpookNationalUniversity
in Korea
and TusneemKausar from
the University of Sargodha, Pakistan. The characteristic aroma, texture and
colourod sesame seeds
are developed by roasting, which is carried out before the oil is extracted
by pressing. Korea
is a major importer of sesame seed oil so needs to be assured of its safety,
regardless of the processing steps.
The researchers bought sesame seeds from local markets
and gamma-irradiated a portion at doses up to 4 kGy.
Then treated and untreated seeds were steamed or roasted and some of the
roasted seeds were subjected to a commercial pressing method to extract the
oil. Following two different extraction procedures, hydrocarbons and ACBs were removed from the seeds and oils for analysis
by GC/MS with electron ionisation to measure
their concentrations.
Four major ACBS were detected, corresponding to the
various fatty acid components of the TGs:
2-dodecyl- (from palmitic acid), 2-tetradecyl- (stearic), 2-(5'-tetradecenyl)-
(oleic) and 2-(5',8'-tetradecadienyl)- (linoleic).
The levels of all four compounds increased linearly with irradiation dose,
with 2-(5'-tetradecenyl)- being the most abundant,
probably because of the high oleic acid content (38.7%) in sesame seeds.
Steaming, roasting and oil extraction had no marked effect on their
concentrations.
The levels of the hydrocarbons also increased linearly
with irradiation dose and three of them were found only in irradiated
samples. One of them, 1-hexadecene, was absent from untreated (roasting,
etc.) samples so is no good as an indicator of irradiation. However, 1,7-hexadecadiene and 8-heptadecene were present only
after irradiation. The team found that their levels increased after
roasting, steaming and oil extraction, in some case by more than 100%. This
does not affect their suitability as irradiation markers, since it is their
presence, not their content, which is significant.
So, 2 particular hydrocarbons and the ACBs as a group have been confirmed as irradiation
markers in sesame seeds that have been processed further after
gamma-irradiation.
Related Links:
Journal
of Agricultural and Food Chemistry 2008 (Article
in Press): "Characteristic hydrocarbons and 2-alkylcyclobutanones
for detecting ã-irradiated sesame seeds after steaming, roasting, and
oil extraction"
