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Turning Up the Heat

Foods with a naturally high acid content — such as tomatoes, citrus juices, pears, and other fruits — will not support the growth of food poisoning bacteria. In tests, when large numbers of food poisoning bacteria are added to these foods, the bacteria die within a day. (The exact amount of time depends upon the bacteria and amount of acidity.) Foods that have a high acid content, therefore, do not receive as extreme a heat treatment as low-acid foods. They are heated sufficiently to destroy bacteria, yeasts and molds that could cause food to spoil.

Canners and food safety regulators are most concerned about foods with low acid content, such as mushrooms, green beans, corn, and meats. The deadly Clostridium botulinum bacterium, which causes botulism poisoning, produces a toxin in these foods that is highly heat-resistant. The sterilization process that destroys this bacteria also kills other bacteria that may poison or spoil food.

Low-acid canned foods receive a high dose of heat — usually 107 degrees Celsius (250 degrees Farenheit) for at least three minutes. (The amount of time the food is heated, though, depends upon the size of the container and the product.) The canned food is heated in a retort, a kind of pressure cooker.

The coffee creamer on Gardine's desk, however, was packaged differently. Although both the half-and-half and plastic container were sterilized with heat, they were heated separately and then brought together in a sterile environment where the container was filled and sealed. The advantage of this "aseptic processing," a type of canning, is that higher temperatures with reduced heating times prevent deterioration in the quality of the food.

Aseptic processing is the "wave of the present and the future," says Gardine. It is now used for liquids, and scientists are on the way to perfecting the method for canning stews and chowders. However, says Gardine, because solid foods may be more difficult to keep sterile during the filling and sealing period, FDA is being especially cautious in approving uses for aseptic processing.

Finessing the Attack on Food Spoilers

Another critical element in the canned food process is sealing products in air-tight containers. It is essential that air be removed from the container before sealing. Air could cause the can to expand during heating, perhaps damaging the seals or seams of the container.

A telltale sign of loss of this vacuum — and a possibly contaminated product — is a can with bulging ends. (See accompanying article.) If a seal is not airtight, bacteria may enter the can, multiply, and contaminate the product.

The hermetic seal finesses the canning process. The bacteria in a food and container are killed through heating, and at the same time new bacteria are kept from contaminating the food.

The distinction between the canning process and food handling before processing is an important one for food processors and regulators. Last February, 22 students at Mississippi State University became ill after eating omelets made with canned mushrooms imported from China. Similar outbreaks followed in New York and Pennsylvania, affecting more than 100 people. FDA identified the culprit as staphylococcal enterotoxin, a poison produced by the bacteria Staphylococcus aureus.

FDA's investigation suggests that poor sanitation caused the problem, and that the mushrooms were contaminated with staphylococcal enterotoxin even before they were canned. The canning process did not destroy the substance because food preservation processes are not normally designed to destroy staphylococcal enterotoxin, a highly heat-resistant toxin.

Since this incident, FDA and the Peoples Republic of China have been working together to determine the source of the contamination. However, FDA authorities still are preventing mushrooms canned in China from entering the United States. And, says Gardine, FDA is focusing attention on sanitation procedures in imported foods.

Surpassing Napoleon

The canned food principle that won Nicolas Appert his prize of 12,000 francs has endured over the years. What might surprise Appert, however, is how his discovery is making food shopping and storing easier for the 20th century consumer.

Those who order coffee at fast food restaurants now also are served canned half-and-half, which has been transported and stored without concern about refrigeration. Hikers can take flexible pouches of canned food on backpacking trips without having to worry about saving water to reconstitute freeze-dried meals. And, in this society of microwave owners, Americans who don't have time to prepare a well-balanced meal can pick up a plastic container filled with a canned, nutritious dinner.

Tags: Food Safety

About the Author

www.fda.gov
FDA is A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the US, these products must be approved by the FDA before they can be marketed.