The Weekly Newsmagazine of Science
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Sniffing out bad food Seafood is one of those commodities with a perilously short shelf life. In but a few days, a good scallop can go bad and an unfrozen salmon can begin to reek. Moreover, with imports today accounting for more than 70 percent of the seafood eaten in the United States, the fish entering domestic ports is anything but a "catch of the day." Before a mahi mahi hauled out of Ecuadorian waters sees a truck with ice on it, "that fish is probably 6 to 10 hours old," notes Walter Staruskiewicz, a research chemist with the Food and Drug Administration's seafood-inspection program in Washington, D.C. So that mahi mahi is already incubating a fair number of bacteria—and still up to 24 hours from an airport that can fly it to the States. "That's the 'fresh-fish' business," he says—and what makes regulating the safety of fresh seafood so challenging. In fact, he notes, "almost all of your spoilage [in seafood] occurs either in water, on the boat, or before it gets to a processing plant." For processed fish, such spoilage may set in 18 months before a consumer ever sees their dinner. Though federal inspectors attempt to nose out less-than-fresh seafood by smell, experienced judges are aging—and often on the cusp of retirement, notes Staruskiewicz. In fact, he observes, FDA has only some 30 inspectors who can nose out an iffy, not yet stinky, fish. That's why he's excited about the prospects for air-sampling devices known as electronic noses. Able to measure volatile chemicals in the air, they compare any odiferous bouquet they're presented against the patterns of smells they've been trained to recognize. Initially developed to spot airborne pollutants and other volatile chemicals, researchers look to the day when the technology will be able to detect faint whiffs of even buried hazards—from TNT (SN: 11/21/98, p. 327) to land mines (SN: 3/28/98, p. 202). For now, they're exhibiting great promise in signaling suspicious seafood and other questionable commodities. Installed on a factory assembly line, which may process up to 600 tons of fish daily, such mechanical bloodhounds might sniff out nascent spoilage. Seafood buyers could also use them to avoid paying for questionable products. And Staruskiewicz's lab is exploring their potential to help the agency's dwindling federal inspection force confirm their food-safety analyses with objective data that will stand any test in court.
A shrimpy nose At the University of Florida, food-processing engineer Murat Balaban has been working with FDA seafood inspectors to develop an electronic nose that really knows shrimp. He uses off-the-shelf hardware, then trains it to distinguish a sweet-smelling crustacean from a stinky one.
By the finish of the third shrimp school that the device attended, Balaban says, "our nose could predict what FDA's inspectors were going to say 100 percent of the time." What the electronic nose can't do, at least yet, is pick out which stinky samples are pathogen-tainted. Most of the reek it detects reflects simple decay—a problem that makes food unpalatable but often not necessarily sickening. The big health risks come from microbial and parasite contamination, which may leave no tell-tale sensory clues. However, Staruskiewicz notes, he has preliminary evidence that certain microbial poisoning agents may leave behind subtle odors that signal their presence. It's probably not their toxins that can be sniffed out, he says, but instead some byproduct produced by the bacterium or other poisoning agent. On the horizon, Balaban says, are combined sensors that will marry an electronic nose with robotic fingers and mechanical eyes. His lab has already developed a prototype that in a few minutes can sniff shrimps for off smells, squeeze the crustaceans to evaluate their texture, and scan the sample to gauge each individual's size. It also detects browning and will even quantify the extent of dark spots marring a product's value. Staruskiewicz points out that these devices will not substitute for human inspectors. Indeed, Balaban says, "We don't want to replace them, just provide them with better tools to do their job." Further Readings:
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This week's Food for Thought has been prepared by Janet Raloff, senior editor of Science News. |
He's tapped the experts who come to his campus for a week-long "shrimp
school" that FDA convenes every year. National experts take a whiff of
shrimps and pronounce whether they are good, bad, or questionable. It's meant as
a training session for seafood inspectors. However, Balaban notes, "as soon
as they're done with a sample, we put it under 'the nose' in our lab," give
it 4 minutes to process the smell, and then instruct the device on how to rank
the aroma.Copyright © 1999 Science Service