The Weekly Newsmagazine of Science
June 12, 1999
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Irradiated Ice Cream and Cake
The home baker usually doesn't have to worry much about spoilage in pies and cakes. They don't last long enough to go bad.
For commercial bakeries that ship their pastries and other confections, fungi can put a serious dent in the bottom line. It can take nearly a week to move breads, fresh cakes and other baked goods across country. By the time the goodies hit grocery shelves, unappetizing colonies of mold may already be evident.
In Bombay, India, where microbiologist Rahul Warke works, the tropical climate and frequent lack of refrigeration conspires with molds and bacteria to blight foods even faster. When a commercial U.S. bakery approached Warke's team at the University of Bombay asking for help in extending the shelf life of its products, one suggestion immediately jumped to mind: irradiation.
Manufacturers often use sorbic acid (also noted as sorbate on the package) as a mold-retarding agent. To pack a truly powerful punch, however, bakeries need to add quite a bitenough that discerning consumers may complain about an objectionable aftertaste.
The same thing is true of irradiation. Pump gamma rays through a fat-filled confection to kill all the microbes present and those fatty lipids will oxidize, creating a rancid taste.
What Warke's team did was marry the twosorbic acid and food irradiationso that low doses of each would be sufficient. Applying low doses of the chemical preservative (0.2 percent by weight) and of irradiation (1 kilogray or less) protected cakes "amazingly," Warke reported at the American Society for Microbiology meeting last week in Chicago. "With this combination treatment," he told Science News Online, "we could increase the shelf life of a cake from just 7 days to almost 4 months."
His group, which is patenting the combo, says bakeries have shown significant interest in commercializing the technology.
The cold trutha cone of germs
At the meeting, Warke also reported data from a survey that his team conducted of ice cream purchased in and around Bombay. Many samples of the frozen treats contained common, potentially life-threatening foodborne pathogens, such as Listeria and Yersinia.
Nor are germ-ridden ice creams a problem only in developing countries. Federal epidemiologists traced the largest salmonella outbreak ever recorded in the United States to contamination of a nationally distributed ice cream (see related story).
Standard means of sterilizationchemical treatments or heatingaren't an option for foods that should remain 70°C to 90°C. So, how's a manufacturer to kill any freeloading microbes that may have stowed away in a gallon of creamy dessert? Again, Warke recommends irradiation.
Previously, researchers had zapped frozen snacks with 40 kilograys of X rays. However, as with cakes, that heavy dose of radiation oxidized the fats that give rich ice creams their velvety taste. "So, we've turned to really low doses," Warke says, "in the range of between 1 kilogray and 2 kilograys."
In tests with strawberry and chocolate ice creams, the researchers found that the irradiation killed germs but left no aftertaste. Indeed, they could up the dose to 5 kilogray with no flavor deterioration. Not so with vanilla. Except at the lowest of the tested doses, taste panels could pick up flavor minor changes.
Tobacco is another solid candidate for low-dose irradiation, Warke believes. "People have no idea how much bacteria and fungi they can ingest from chewing tobacco," he says. He has sometimes measured heavy microbial contamination in this product. "I have studied the process under which it is manufactured, and it doesn't really have any checks for bacterial or fungal counts," he says.
Because some fungi have been linked to the development of oral and gastric cancers, he notes, tainted tobacco could prove a risk factor for more than just gut-wrenching food poisoning. "But when we used irradiation, it worked," killing off the potentially pathogenic microbes, he says.
Currently, Warke observes, irradiation is not approved for any of these proposed applications-in the United States or India. However, with the safety and efficacy studies that are now underway, he says, that may change.
This Food for Thought was prepared by Janet Raloff, senior editor of Science News.
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