Rays

Machines used for food processing are more powerful versions of those used in hospitals and dental offices to take X ray pictures. To produce the X rays, a beam of electrons is directed at a thin gold plate or other metal, producing a stream of X rays beneath the metal plate, which then penetrate the food being processed. X rays can also penetrate deeply and can be switched on and

Figure 4.1. (a) The Rhodotron TT100, a 10-MeV/35-kW recirculating electron beam accelerator, showing the circular area where electrons are generated and accelerated; (b) general overview of a suggested layout of a food irradiation plant employing a rhodatron accelerator—the arrow points to the radiation vault where electrons scan back and forth across a conveyor system carrying the products to be irradiated. (Both photographs courtesy of Ion Beam Applications, Lourain-La-Neave, Belgium.)

Figure 4.1. (a) The Rhodotron TT100, a 10-MeV/35-kW recirculating electron beam accelerator, showing the circular area where electrons are generated and accelerated; (b) general overview of a suggested layout of a food irradiation plant employing a rhodatron accelerator—the arrow points to the radiation vault where electrons scan back and forth across a conveyor system carrying the products to be irradiated. (Both photographs courtesy of Ion Beam Applications, Lourain-La-Neave, Belgium.)

off, and although they require heavy shielding, radioactive substances are not involved. In the newer X ray machines, an electron beam collides with a tungsten target plate, creating X rays capable of completely penetrating food products.

We need to give these irradiation processes an opportunity to work on our behalf, and to do so we address two questions: Why food irradiation, and how does it affect food? The "why" is straightforward; it's protective, preserving, and preventive.

TABLE 4.1. Irradiation Doses Permitted in Foods

Product Dose (kGy)

TABLE 4.1. Irradiation Doses Permitted in Foods

Product Dose (kGy)

White Potatoes

0.05-0.15

Fruit

1 maximum

Fresh vegetables

1 maximum

Poultry, fresh or frozen

3 maximum

Shell eggs

3 maximum

Meat, uncooked, chilled

4.5 maximum

Meat, uncooked, frozen

7.0 maximum

Seeds for sprouting

8 maximum

Spices

30 maximum

In meat and poultry it kills salmonella, E. coli O157:H7, listeria, Campylobacter, toxoplasma, and other bacteria at levels of 99.9%. Irradication also

• Readily removes Yersinia and the Trichinella worm in pork.

• Prevents sprouting of potatoes and mold on strawberries.

• Kills insect larvae in grains, fruits, and vegetables and kills insects and bacteria in spices.

• Will delay ripening of fruit, increasing shelf life of many products that are closer to their fresh state.

With all this, what can we expect of the irradiated food?

The many studies done over the past 40 years indicate that irradiation produces no greater nutrient loss than does canning. Some foods may taste slightly different, just as pasteurized milk tastes slightly different than unpasteurized milk.

If irradiation is done at low temperatures, vitamin loss is minimal. Thiamine, a B-complex vitamin, is more sensitive to cooking temperatures than it is to radiation. Up to the maximum 10 kGy dose, there is no significant loss of proteins, fats, or carbohydrates, and minerals are not at all affected by irradiation.

Irradiation energy is measured in units of grays (Gy), the amount of energy transferred to the food. Irradiation of food is delivered in kilograys. One thousand (1000) grays equals one kilogray (kGy). A single chest X ray provides a dose of 0.5 mGy, a thousandth of a gray unit (Gy). By way of comparison, the FDA has approved the use of 3 kGy for irradiation of raw chicken to kill salmonella. Table 4.1 provides the approved dose levels for a sampling of foods approved for irradiation.

Irradiation can increase shelf life, but it cannot improve spoiled food Off-odors and off-tastes cannot be undone. Nor does irradication destroy preformed bacterial toxins already in food, or viruses that may also be present. Irradiated foods require refrigeration and must be handled and cooked safely. Now, what of safety?

Evidence from numerous studies conducted worldwide over the past 50 years informs us that chemicals formed in irradiated food are generally the same as those produced during canning, cooking, and other forms of food preservation, and do not put consumers at risk. The standard procedure in those studies is to feed laboratory animals the irradiated food and look for impacts on longevity, reproductive capacity, and tumor incidence [11]. A recently published study provides some guidance. This experimental study sought to determine whether 2-alkylcyclobutanone (2ACB), a radiolytic derivative of triglyceride, promoted colon cancer. In this study, one group of rats were fed 2ACB, while another group received a 2ACB-free diet for 6 months. Both groups received injections of a known chemical carcinogen. The question was whether 2ACB would enhance tumor growth. The researchers found that the 2ACB-treated animals had more tumors than did the control group. However, the authors inform us that the 2ACB-treated rats received 1000 times more 2ACB than would be found in any irradiated food eaten by humans. They also indicate that irradiated foods may contain several components that may reduce the bioavailability of 2ACB. Furthermore, they say that the benefits of food irradiation are becoming increasingly recognized [12].

It has been suggested that there is a potential for chromosomal damage to those who eat irradiated food. This, of course, refers back to the notion of induced radioactivity in such foods. According to the International Consultative Group on Food Irradiation (an FAO/WHO/IAEA affiliate), irradiation cannot induce radioactivity no matter how long the food is exposed to a radiation source, or how much of the energy is absorbed [13]. It's worth recalling that photons do not release neutrons, so that without radioactivity, chromosomal damage cannot occur.

Yet another concern raised about food safety has been the notion that irradiation could increase the virulence, the pathogenicity of bacteria. The FDA has found no evidence of such a response. In fact, it has been found that pathogenic bacteria that survive irradiation are destroyed at lower cooking temperatures than are unirradiated pathogens. It is also worth considering that because the FDA defined irradiation as an additive rather than a process per se, it had to undergo extensive testing to ensure its safety. Additionally, the U.S. General Accounting Office reviewed 6000 published articles and concluded that "the benefits out weigh the risks" [14].

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