OSU-developed oyster processing techniques prevent food poisoning

Article photo
These oysters are served on the half shell in Astoria, Oregon.

The number of food poisoning cases caused by eating raw oysters is on the rise, but food scientists at OSU’s Seafood Research & Education Center are finding new ways to protect people who enjoy this seafood delicacy. Researchers have developed two different post-harvest processing techniques to remove the harmful bacteria that sicken 45,000 oyster-lovers in the United States each year.

The United States produces 27 million pounds of oysters annually. Most processors only rinse oysters to remove surface contaminants, and the refrigerate them alive until they are shucked and served raw. Seafood product labels and restaurant menus warn consumers that eating raw shellfish may increase the risk of food poisoning.

Oysters grown in the cold-water bays of the Pacific Northwest contain the bacterium Vibrio parahaemolyticus. One of the new processing methods uses high-pressure washing to inactivate the bacterium. Oysters are banded shut and placed in cylinders where they are washed in cycles of pressurized water. The process not only removes harmful bacteria but allows oysters to be safely stored after processing for 6-8 days when refrigerated, 16-18 days when kept on ice.

The high-pressure washing technique is used by at least two national oyster processors: Nisbet Oyster Co. in Washington and Motivatit Seafoods in Louisiana. The method is gaining acceptance, although it requires substantial investment in new equipment.

Another purification method under development is called refrigerated depuration. It was pioneered by the late Yi-Cheng Su, who was a researcher the OSU seafood center. Oysters are placed in chilled seawater sterilized with ultraviolet light. The shellfish naturally filter the clean water through their digestive systems, which eliminates more than 99 percent of the bacteria. Dr. Su demonstrates how it works in this video.

Sources: Christina DeWitt, director of OSU Seafood Research & Education Center; Joy Waite-Cusic, OSU food safety microbiologist. 

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