Getting Enough Oxygen?

"The concern was over the risk of botulism which occurs in situations of low oxygen," Brackett said. "And these bags are designed to contain low concentrations of oxygen."

Botulism affects the nervous system. Symptoms include nausea, vomiting, fatigue, dizziness, headache, dryness of skin, mouth and throat, constipation, paralysis and double vision.

"The bacterium grows in foods and produces a toxin. You eat the toxin, and it makes you ill," Brackett said.

Specially Designed Bags

To assure safety, food scientists in the UGA College of Agricultural and Environmental Sciences studied the convenient packages before they were ever introduced to the public.

"The food industry wanted to be sure the packages were safe. And to date, there hasn't been an outbreak connected to a bagged salad," Brackett said. "And millions have been sold."

Although the potential for risk is high, Brackett said the packages for ready-made salads are designed to prevent food-borne illness.

"They're engineered so that when the product respires, it produces more carbon dioxide and reduces the amount of oxygen," he said. "The carbon dioxide slows the product's natural aging process. And this slows down deterioration."

The packages actually prevent a natural process. "Changing the gases in the bag slows the natural aging process of the food," Brackett said. "After all, it's a plant, and plants want to break down. That's how they release their seeds."

The food industry uses these special bags, he said, to extend the product's shelf life.

Don't Try This at Home

"When there might be a problem is if small companies or homeowners make 'Baggies' of vegetables in an attempt to do the same thing on a small scale," said Brackett.

Brackett said the main problem associated with packaged salad greens and ready-to-use vegetables is their long shelf lives.

Looks Can Be Deceiving

"People think they can keep them forever, just because they look good," he said. "In this case, the quality and the safety have no relationship. The product can look really good and be bad for you."

In this case, Brackett said, spoilage also works to the consumer's benefit. "We found the product would visibly spoil before there was a risk of food-borne illness," he said.

The best safety rule, he said, is to go by the "use-by" date on the package.

"If the product's bag says 'Use by Oct. 20,' use it by that date. Don't keep it just because it looks good," he said. "Some pathogens can grow at refrigerated temperatures. The longer you keep the product, the more chances the harmful bacteria have to grow in populations."

(Article and photograph by Sharon Omahen, University of Georgia College of Agricultural and Environmental Sciences.)