Agriculture Reference
In-Depth Information
organoleptic changes because in the frozen state the
chemical reactions that bring about the desired effects of
irradiation are hindered and a higher dose is necessary
to achieve the same objective.
When treating
frozen
products, time in the irradiator
should be kept to a minimum so that any temperature
rise is not significant. Similar considerations regarding
dose and irradiation conditions also apply to other prod-
ucts such as frogs' legs and shellfish.
the radionuclide continuously emits radiation and when
not in use must be stored in a water pool, whereas machines
producing high-energy electrons can be switched off and
on. This naturally influences the financial feasibility, and a
plant needs to be in continuous operation.
Uses
Some of the uses of ionising radiation are as follows:
1
Decontamination of food ingredients such as spices
2
Reduction in of the numbers pathogenic micro-
organisms such as
Salmonella, Campylobacter
and
Listeria
in, for example, meat and meat-type products
3
Extension of shelf life of fruits, vegetables, meat and
meat products
4
Insect disinfestation of grain, grain products and
tropical fruits
5
Inhibition of sprouting in potatoes, onions and garlic
Other requirements
The benefit to be gained from using irradiation, whether,
for example, to control food-poisoning micro-organisms
or to disinfect grain, will only be achieved if the food
being treated is of excellent quality and is stored under
suitable conditions before and after irradiation. This
often involves chilled or even frozen storage, and,
depending on the product, humidity control may also be
necessary. The need to combine irradiation with suitable
storage highlights the point that irradiation is not a tech-
nology that can stand alone. It is one technology among
many others which in some cases may have advantages
over the more conventional food preservation methods.
The Food Irradiation Regulations 2009 require
licensing of premises which can carry out irradiation.
The seven permitted descriptions of food are fruits,
vegetables, cereals, bulbs and tubers, spices and condi-
ments, fish and shellfish and poultry (see also 'Further
reading').
Effectiveness
The effectiveness of the process depends on the quality
of the raw material, dose applied, temperature during
irradiation, type of packing and storage conditions
before and after irradiation.
Pathogens such as
Salmonella
and
Campylobacter
are
sensitive to fairly low levels of ionising radiation. As the
radiation dose increases, more micro-organisms are
affected, but a higher dose may simultaneously introduce
organoleptic changes, and there needs to be a balance
between the optimum dose required to achieve a desired
objective and that which will minimise any organoleptic
changes. With
fresh poultry
carcases, an irradiation dose
of 2.5 kGy (kilogray) will virtually eliminate
Salmonella
and extend the shelf life of the food by a factor of about 2
if the storage temperature post-irradiation is maintained
below 5°C. (The gray is the SI unit of absorbed radiation
dose, equivalent to transfer of 1 J of energy per kg of
product being treated (1 J/kg).) Irradiation of poultry
was approved in the United States in 1990.
High pressure
An interesting development, currently attracting a great
deal of worldwide interest, is the use of high pressure.
The pressures involved are immense, greater than at the
bottom of the deepest ocean, which is over 6.5 tonnes
per square inch. Work in Australia has shown that the
cooked tenderness of meat can be improved by such
treatment, either before or after rigor mortis, and
Japanese workers have demonstrated that the time
required for conditioning can be decreased. The micro-
biological quality of comminuted meat products can be
improved, offering potentially increased shelf life. The
water binding of beef patties is increased. However, all of
this work is very much in its infancy and is likely to
involve further capital investment and many hours of
development to bring high-pressure-treated meat and
meat products into the marketplace.
Organoleptic changes
Higher doses will give an even greater reduction in the
numbers of micro-organisms, but at doses of about 5 kGy
or above, odour and flavour changes may be produced in
the food during storage which will render it unaccepta-
ble. These are caused by the formation of volatile
sulphur-containing substances - hydrogen sulphide, car-
bonyls, amines, etc. Hydrogen sulphide odour is lost on
subsequent storage, and different odours develop. While
beef is especially susceptible to the development of these
unpleasant odours and flavours, pork is much less affected.
Irradiation doses up to 10 kGy can be applied to fro-
zen poultry (−18°C) without causing any unacceptable
References
Berends, B.R., Van Knapen, F., Snijders, J.M.A., et al. (1997)
International Journal of Food Microbiology
, 36, 199-206.
Bolton, D.J., Pearce, R.A., Sheridan, J.J., et al. (2002)
Journal of Applied
Microbiology
, 92, 893-902.
