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Food Irradiation and Vitamin Loss

In 2007, Indian mangoes made their first trip in 18 years to the United States. While the U.S. government hailed the fact that irradiation had been used to kill any pests that might have been living in or on the fruit before its overseas ride, consumers should question how exposing mangoes to high levels of ionizing radiation affects the nutritional quality of the fruit. During storage, for example, irradiated mangoes can lose more than half of their vitamin C. Watch for that misleading green logo, if you see it on fruit or vegetable, don’t buy it.

Irradiation has three main purposes: to eradicate pests such as fruit flies on harvested crops, to extend the shelf life of food, and, with a higher radiation dosage, to kill disease-causing microorganisms such as E. coli and Salmonella.

In addition to Indian mangoes, irradiated lemons from South Africa can now be shipped to the United States. Starting on July 23, 2007, Thailand was allowed to export irradiated mangoes, mangosteens, pineapples, rambutans, litchis, and longans to the United States. Additionally, the Mexican company Phytosan plans to build two facilities to irradiate tropical fruits for export to the United States, although its plans have been met with significant local opposition. Some spices and seasonings also are irradiated, but many brands available in grocery stores are not.

Within the United States, some meat is irradiated, but it has not been commercially successful due to public distrust. Since 2004, when schools were first offered irradiated meat through The U.S. Department of Agriculture’s National School Lunch Program, not a single school system has purchased irradiated ground beef from USDA. Hawaii hosts one facility that irradiates papayas and other tropical fruits. However, plans for a second facility on Oahu have been delayed by local opposition and a legal challenge.

When food is irradiated, ionizing radiation reacts with water in the food, causing the release of electrons and the formation of highly reactive free radicals. The free radicals interact with vitamins in ways that can alter and degrade their structure and/or activity. The extent to which vitamin loss occurs can vary based on a number of factors, including the type of food, temperature of irradiation, and availability of oxygen. Nonetheless, vitamin loss almost always increases with increasing doses of radiation.

The destruction of vitamins continues beyond the time of irradiation. Therefore, when irradiated food is stored, it will experience greater vitamin loss than food that has not been irradiated. Cooking further accelerates vitamin destruction in irradiated food more than in non-irradiated food.

The very fact that irradiation is used to extend the shelf life of food compounds the issue of vitamin loss. For example, an irradiated mango can sit in a crate for a longer time without rotting, but it will continue losing vitamins for the period after which a non-irradiated mango would have been discarded. Therefore, a direct comparison between the vitamin content of irradiated versus non-irradiated food stored for an equal length of time actually understates the extent of the problem.

What you can do: before biting into an irradiated mango from India or Thailand, consumers should be aware that these fruits are likely less nutritious than their counterparts that have not been exposed to radiation.

• Be on the lookout for the irradiation symbol on the label, and avoid such foods.
• For the highest vitamin content, buy locally produced foods, which likely are fresher than food from hundreds or thousands of miles away. Ask your senators and representative in Congress to support accurate labels on irradiated food, and not allow the Food and Drug Administration to weaken labeling rules by allowing some irradiated food to be labeled as “pasteurized” and other irradiated food to be sold unlabeled.