UpDate - Vol. 12, No. 38, Page 6
August 5, 1993
Under pressure; New technique will extend life, quality of seafood 

     An estimated 65 percent of the seafood sold in the United States is
eaten raw or unprocessed. Better food preservation techniques may make it
possible for enthusiasts to indulge their passion for raw or minimally
processed seafood with less risk of food-borne illness.
     Dallas Hoover, a microbiologist in the Department of Food Science in
the College of Agricultural Sciences, is investigating the use of high
hydrostatic pressure treatment to improve the quality, shelf life and
safety of oysters and crabmeat. The process makes it possible to inactivate
vibrio, listeria, salmonella and other harmful microorganisms in foods
without heat or chemical additives.
     "Treating food with hydrostatic pressure is like exposing it to the
kind of pressure that exists at the deepest part of the ocean," Hoover
explained. "It's like being under miles of water that's not moving."
     At these pressure levels, microbial cells don't explode, but the cell
membrane starts to leak, and internal cell components lose their viability.
Since heat is not used, the treated food undergoes minimal flavor, color
and textural changes and more closely resembles its fresh form.
     Foods respond differently to hydrostatic pressure, and deactivating
microorganisms requires various amounts of pressure.
     "For example, oysters that have been pressurized are a bit flatter
than raw oysters," Hoover says. "They taste the same, but the bacteria and
parasites have been inactivated."
     Pressurization is also quicker than other food processing methods, and
it uses less energy.
     The process is simple. First, the food to be treated is sealed inside
a polyester bag. The bag is then sealed inside another bag filled with
water. This package is placed inside a chamber filled with water, the
chamber is closed securely and an air compressor that pumps in liquid to
build pressure is turned on.
     The unit Hoover uses for his tests takes about three minutes to reach
3,950 atmospheres-58,000 pounds per square inch. Decompression takes 30
seconds or less.
     Hoover is cooperating in a $107,800, two-year Sea Grant study designed
to investigate the use of hydrostatic pressure treatment to improve the
microbial safety and quality of seafood. Dietrich Knorr, a biotechnologist
in the food science department, and Doris Hicks, seafood specialist in the
University's College of Marine Studies, are also working on the project.
     "Pressure-treating seafood makes sense," Hoover says. "A lot of people
like to eat raw fish and shellfish. Bacterial contamination of seafood is a
very real health risk. And scientists are now finding that fish parasites
such as eel worm and seal worm can infest humans. These parasites are also
pressure-sensitive."
     High-pressure treatment of seafood would have several advantages if
the technique becomes commercially feasible, the microbiologist said.
Consumers would benefit from a safer, fresher seafood supply. The U.S.
fishing industry would benefit from increased consumer demand, potentially
longer shelf life of seafood and increased profits. Seafood products also
would become more readily available to inland markets.
                                        -Doris Crowley