When considering the best time of year to eat oysters, clams, mussels, and other mollusks, consumers may often hear the advice, “Never eat shellfish unless there is an R in the month.” This rule of thumb suggests that it is safer to eat shellfish from September through April and to avoid it from May to August. Although it is true that shellfish are more active during warm months and are, therefore, more susceptible to contamination, eating raw or undercooked mollusks may pose a safety hazard at any time of year.
Vibrio vulnificus, a naturally occurring bacterium found in marine waters with low salinity levels such as bays and estuaries, is commonly found in shellfish. Consuming raw or undercooked shellfish containing the bacteria could lead to an infection with symptoms including vomiting, diarrhea, abdominal pain, and even septicemia. Oysters and other mollusks can also be carriers of the hepatitis A virus, an acute infectious disease of the liver.
Researchers with the U.S. Department of Agriculture’s (USDA) Agricultural Research Service (ARS) scientists are studying ways to enhance the food safety of popular shellfish. Specifically, USDA molecular biologist David H. Kingsley, along with a team of researchers at Delaware State University in Dover, is trying to develop ways to decontaminate mollusks while not destroying their flavor, texture, color, and overall integrity.
The team has been experimenting with a commercial procedure known as high pressure processing, or HPP, a technique first developed by Blaise Pascal in the 17th century to inactivate certain microorganisms in food. Today, HPP is already in widespread use within the food industry; however, Kingsley explains that this ARS research project is the first to determine that the HPP method is also effective against some foodborne viruses.
HPP equipment compresses water to create intense pressures as high as 90,000 pounds per square inch. Normal atmospheric pressure is about 15 pounds per square inch at sea level. In tests targeting hepatitis A virus, the cause of a contagious liver disease, the team showed that an HPP treatment of 60,000 pounds per square inch of pressure for five minutes inactivated 99.9 percent of the virus in oysters that had been exposed to the pathogen in laboratory tanks.
So far, Kingsley and his colleagues are happy with their success. Yet, the scientists have not perfected the HPP method since they have noticed that the taste of the seafood is sometimes altered as a result of the intense pressure. In the coming months, they will continue to investigate ways to make improvements without reducing the levels of decontamination achieved.