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Counting electrons can cut seafood analysis time
By Allison Matthews
MISSISSIPPI STATE -- A lack of uniform freshness standards in the seafood industry and an intriguing visit to Dauphin Island, Ala., led Mississippi State University food science professor Douglas Marshall to brainstorm methods of improving seafood testing.
Although consumers who enjoy seafood expect their meals to be safe and fresh, the industry has employed a rather subjective means of measuring the quality of ocean harvests. Processors have relied on sensory methods to measure characteristics such as aroma, texture and color. Chemical and microbiological testing methods have long analysis times and only seem to verify the sensory tests.
Marshall said the lengthy analysis time of chemical or microbiological tests wastes product shelf life and requires highly trained analysts to interpret results. He recognized the need to speed up seafood testing and eliminate subjectivity. He developed new tests that give fast results using impedance technology, which measures the flow of electrons through food.
"We've tried to use objective measurements of quality so that any inspector administering these tests will get the same results. This data correlates to results of sensory testing, but impedance eliminates the subjectivity of the processor's perspective," Marshall said.
Standard chemical and microbiological testing can take 24 to 48 hours, but impedance technology allows testing to be finished in as little as 30 minutes.
Marshall thought of impedance as an effective tool for the seafood industry after he met with scientists at the Food and Drug Administration's Fisheries Research Branch at Dauphin Island in 1990. The FDA scientists were trying to find more reliable indicators of seafood freshness.
Testing for quality and safety is very important, both to meet federal standards and to ensure consumer satisfaction and health. About 5,000 people in the United States die each year from food-borne illnesses. Seafood causes a large number of outbreaks, but it is not responsible for as many individual cases of food poisoning as other foods.
Impedance technology, using different applications, allows rapid testing of crustacean shellfish and mollusks. Crustaceans include seafood with an exoskeleton or soft shell, such as lobsters, crawfish, shrimp and crabs. Mollusks are those without skeletons that live in hard shells, including oysters, clams, mussels and scallops.
Marshall's rapid impedance tests can detect spoilage indicators in crustaceans and safety indicators in mollusks. Marshall explained the importance of testing safety of seafood such as oysters -- which are the primary mollusks Americans consume -- because they are often eaten raw.
Oysters are known to transmit a few serious pathogens. Marshall's tests are designed to quickly detect and count pathogens present so seafood that is safe may be supplied to consumers more quickly, without wasting freshness time. The tests also reliably indicate foods that violate FDA safety standards and should not be passed to consumers.
"These pathogens are primarily associated with the consumption of raw oysters. They are not a problem when seafood is cooked," Marshall said.
The pathogens, specifically Vibrio parahaemolyticus, which is most common in the United States, are present in all raw oysters. Scientists believe the pathogens are dangerous only when the number present exceeds a certain level established by the FDA. Impedance also can test for Vibrio vulnificus, a rare but deadly pathogen associated with oysters harvested off the Gulf Coast.
"The FDA has a regulatory limit for molluscan shellfish of less than 10,000 Vibrio bacteria per gram," Marshall said.
To test the food samples using impedance technology, processors place specimens into a well of a testing module. Each module contains 16 wells, and within each well is a pair of electrodes. The modules are placed in a Bactometer Processing Unit and tested with a few simple computer commands. The Bactometer counts the number of bacteria so processors can determine whether the samples meet safety standards. Marshall said up to 128 food samples can be tested simultaneously.
Before reaching the consumer, processors may conduct food safety and quality checks at a variety of points along the processing chain. Seafood is tested as soon as boats bring their harvests to the docks, again by processing plants and then by clients, such as supermarkets, who buy from the processing plants.
"Lastly, consumers do their own quality checks at the supermarket counters," Marshall said. The FDA also may double-check for quality and safety at any point in the food processing and distribution line.
For more information, contact: Dr. Doug Marshall, (662) 325-8722