Food preservation by ionizing radiation
Overview
Ionizing radiation corresponds to electromagnetic radiation or particulate energy associated with a greater than 10 eV (electron Volt). Below this value of energy, radiation is "non-ionizing" and there class including radiation, infrared, ultraviolet, or electromagnetic fields of extremely low frequency (microwave).
With the energy that is associated with ionizing radiation are capable of moving the electrons of atoms and molecules and converting them into ions, hence the term "ionizing radiation". The term "ionizing radiation" is also used for this type of treatment.
Ionizing radiation are applied to foods to improve their keeping quality. Foods treated with ionizing radiation are known as "irradiated". They are not "radioactive."
Types of ionizing radiation
The irradiation of food can be carried out by three types of ionizing radiation:
- X-rays: X-rays are produced by aircraft operating at an energy level equal to or less than 5 MeV.
- Accelerated electrons: The electrons are accelerated systems obtained by operating at a level of energy equal to or less than 10 MeV.
- Ray γ: γ-rays are produced by radioactive isotopes (radionuclides), which is either cobalt 60 or cesium 137.
Irradiation dose and dose rate
Dose irradiation
The dose of irradiation is the amount of energy absorbed by the food quantity of mass. In SI unit, the radiation dose is expressed in Gray (or Gy) 1 Gy corresponds to the absorption of an amount of energy of one joule per kilogram of food. The old unit, the rad is still widely used:
1 rad = 10-2Gy
Internal jargon for this type of radiation treatment class into three categories, depending on the dose applied:
- The radappertisation (20 to 50 kGy): Destroys all microorganisms. Also referred to as "radiosterilization.
- The radicisation (10 kGy or less): Destroys all non sporulating pathogens. Also referred to as "radiopasteurization.
- The radurisation (5 kGy or less): Reduces the microbial load without affecting the product.
In 1980, the Joint FAO (Food and Agriculture Organization) / WHO (World Health Organization) / IAEA (International Agency for Atomic Energy) agreed, after extensive toxicological studies, the safety of irradiation for doses below 10 kGy (10,000 Gy). More recently, in 1997, these agencies have concluded that no maximum dose should not be accepted. However, the Codex General Standard for irradiated foods (CODEX STAN 106-1983, REV. 1-2003) states that the maximum absorbed dose for a food must not exceed 10 kGy, except where necessary to get legitimate technological results.
Dose rate
The dose rate is determined by the dose absorbed by the food, per unit of exposure time. This is the power that can be expressed in kilowatts per kilogram of food or kGy per unit time.
The radiation dose and dose rate are related by the following formula:
D = D '. T
D: Dose Irradiation
D ': dose rate
t: Time exposure of the food at the source of irradiation
Effect of ionizing radiation on food conservation
The effect of ionizing radiation on microorganisms is due primarily to chemical modifications of DNA and RNA that lead to inhibition of growth or cell death. Apart from these direct effects of ionizing radiation should be added the indirect effects associated with the presence of radiolysis products such as hydrogen peroxide.
The kinetics of destruction of microorganisms by ionizing radiation is directly related to the applied dose following an exponential law of type:
N = N0.10-(D/D10) = N0.10-[(D’.t)/D10]
N0: initial number of microorganisms.
N: Number of surviving microorganisms after application of the radiation dose D.
D ': dose rate
t: Time exposure of the food at the source of irradiation
D10: Rate corresponding to the destruction of 90% of the cells of microorganisms.
It is obvious that for a given radiation dose, the efficacy is even lower than the number of microorganisms initially present in the product will be high. This treatment therefore does not question the usual hygienic measures. In addition, the ionizing radiation at doses usually used, does not destroy toxins already produced by microorganisms before treatment.
The factor D10characterizes radiorésistance microorganisms, but it is far from being an intrinsic factor of a given species, as it is in the case of heat treatments. dépend de plusieurs autres facteurs comme le débit de la dose, la nature des rayonnements ionisants utilisés et la température du traitement. Indeed, several studies have shown that, in addition to the case D10depends on several other factors as the flow of the dose, the nature of radiation used and the temperature of treatment.
Broadly speaking, we can say that the most radioresistantes are spore forming bacteria, followed by Gram + bacteria that are resistant than gram-. The molds are in the vegetative forms of bacteria. As for yeast, they are also resistant than bacteria less radiosensitive.
The effects of ionizing radiation are not limited to microorganisms in the product: they also disinsect foods (cereals, pulses eg) and to delay the maturation and / or germination of fruits and vegetables by disrupting endogenous enzymatic mechanism responsible for the maturation and / or germination.
Different applications of ionizing radiation treatment
The radiation treatment did not aim to replace all the processes currently used for conservation. Leave the application of this treatment varies from country to country. The processing of spices is becoming more widespread. In fact, these foods are heavily contaminated and there are not many alternatives for decontamination (fumigation with ethylene oxide is now banned because of its toxicity).
In Belgium, the products that can be irradiated are: potatoes, strawberries, onions, garlic, shallot, paprika, pepper, gum arabic, spices and flavorings, vegetables, products for the preparation of infusions, shrimp, frog legs , frozen poultry meat and mechanically deboned. The label of a food containing irradiated or irradiated ingredients must include the treatment.
In France, a fortnight of food and food ingredients can be treated with irradiation: spices, herbs, dried or frozen, onions, garlic, shallots, vegetables and dried fruits, corn flakes and muesli, poultry meat, frog legs , shrimp, etc..
In Canada, food irradiation has been recognized since 1989 either as an additive but as a treatment process in accordance with a regulation under the Act Food and Drugs. It authorizes the use for the following purposes: slow germination of potatoes and onions, to kill insects that infest the wheat and flour, or reduce the number of microbes in spices and dehydrated seasonings.
Adverse effect of food irradiation
Irradiation is a technique of preservation allowed for certain foodstuffs. It is effective and can replace chemical hazardous to health. However, its use should be optimized such kinds to enjoy its benefits without the consumer is a victim of its effects.
Side effects of food irradiation are:
- The destruction of much of the vitamins and nutrients in foods.
- Irradiation blocks the degradation processes of microbial and enzymatic food: food as a strawberry or a shrimp may appear fresher than it actually is (This seems fresh food but it is not; it may have lost much of its nutritional principles). The consumer may be misled because the appearance of the food does not match the aspect that a fruit not treated with the same "age".
- Food irradiation leads to the formation of free radicals, highly reactive products, which react by forming products of radiolysis uncertain, sometimes causing deterioration of the organoleptic characteristics of food. The adverse reaction of radiolysis products on human health can not be ruled out, although it is not yet proven.
- Food irradiation uses of nuclear technology which raises all environmental issues relating to the use of these technologies.
To inform consumers about irradiated foods, the Codex Standard for the Labeling of Prepackaged Foods (CODEX STAN 1-1985), requires that the label of any food that has been treated by ionizing radiation, or containing irradiated ingredients must bear a statement to that effect. The use of the international symbol for irradiation of food, shown below, is optional, but when it is used, it must appear next to the name of the food.
