Food Preservation: The Case for Irradiation

By Sinovic, Dianna

Current preservation techniques can kill bacteria on or in many foods such as milk and eggs, but their use is difficult on raw produce. Meanwhile, the headlines urge us to eat more fruits and vegetables -- often raw.

But how safe are raw foods? We've all heard of foodborne illness caused by contaminated fruits and vegetables, not to mention tainted meat.

Irradiation is slowly gaining consumer acceptance as a way to make foods safer. The Centers for Disease Control and Prevention (CDC) says that like pasteurizing milk and pressure cooking canned foods, treating food with ionizing radiation can kill most bacteria and parasites that would otherwise cause foodborne disease. Similar technology is used to sterilize medical devices so they can be used in surgery or implanted without risk of infection. Irradiation could be used on a variety of foods to eliminate insect pests and replace toxic chemicals that now are routinely used for fumigation of many foods. It can also slow the growth of molds, inhibit sprouting and prolong shelf life.

Specific radiation

Three different irradiation technologies exist, using different kinds of rays: gamma rays, electron beams and X-rays.

  • Gamma rays have been used routinely for more than 30 years to sterilize medical, dental and household products, and for radiation treatment of cancer. Gamma rays can penetrate foods to a depth of several feet. They do not make anything around them radioactive.

  • Electron beams (E-beams) are propelled out of an electron gun that is a larger version of the part of a TV tube that propels electrons into the TV screen, making it light up. They have been used as sterilizers for more than 15 years, according to the CDC. No radioactivity is involved. The electrons can penetrate food only a little over an inch, so the food treated must be no thicker than that. Two opposing beams can treat food twice as thick.

  • The newest technology is X-ray irradiation. The X-ray machine is a more powerful version of the machines used in many hospitals and dental offices to take X-ray pictures. X-rays can pass through thick foods. They require heavy shielding for safety.

When food is irradiated, the high-energy ray is absorbed as it passes through food. The ray gives up its energy, causing the food to be slightly warmed. Irradiation damages the DNA in any microbe, fungus or parasite present, killing the organism. Disease-causing organisms differ in their sensitivity to irradiation. Irradiation works very well to eliminate parasites and bacteria from food, but it will not work to eliminate viruses or prions. Parasites and insects have large amounts of DNA and so are rapidly killed by extremely low doses of irradiation. Bacteria have smaller amounts of DNA, so it takes more irradiation to kill bacteria and bacterial spores, the dormant state of some bacteria.  Viruses are the smallest pathogens that have DNA or RNA, and they are relatively resistant to irradiation at the levels approved for foods. Prions, such as the one that causes “mad cow” disease (bovine spongiform encephalopathy, or BSE), have no DNA, so they also are not affected by irradiation at the levels approved for foods.

A variety of foods have been approved for irradiation in the United States. Irradiation of meats must be approved by both the U.S. Department of Agriculture (USDA) and the U.S. Food and Drug Administration (FDA). Irradiation of fresh or frozen meat and meat products, including hamburger, fruits and vegetables, has been approved. 

Approval Year

Food

Purpose

1963

Wheat flour

Control of mold

1964

White potatoes

Inhibit sprouting

1986

Pork

Kill Trichina parasites

1986

Fruit and vegetables

Insect control, increase shelf life

1986

Herbs and spices

Sterilization

1990 - FDA

Poultry

Bacterial pathogen reduction

1992 - USDA

Poultry

Bacterial pathogen reduction

1997 - FDA

Meat

Bacterial pathogen reduction

1999 - USDA (pending)

Meat

Bacterial pathogen reduction


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