Germs Under Pressure From Science

Every kid knows what it means to be squished like a bug.

These days, scientists are using water under very high pressure--starting at about 37,000 pounds per square inch--to squish bugs we can’t even see, the ones that cause food to spoil or cause illness.

The goal is to make food safe without cooking all the flavor and nutrition out of it.

High-pressure processing is just one of the new technologies emerging to tackle this challenge. Irradiation, being used in moderate doses for raw meat products now sold in the Midwest, may be the best known.

But the process being pioneered here by Fresher Under Pressure may do the least damage to food. The company is a fledgling subsidiary of Flow International, a Nasdaq-traded industry leader whose ultra high-pressure water jets are used to cut everything from disposable diapers and Fig Newtons to 12-inch-thick titanium.

Flow’s sleek stainless-steel processors use ultra high pressure to squeeze the germs--but not the color, flavor, texture or nutrients--out of guacamole, salsa, avocado slices, deli meats, juice and raw oysters.

The process even shucks the oysters as it extends the time these refrigerated foods will keep. Foods are simply placed inside the device--liquids are pumped through--and pressure applied, for a few minutes at most.

Products must contain moisture for the process to work. Food is not crushed because the pressure is uniformly applied--as marine life is not crushed at the bottom of the ocean, where pressure is about 15,000 pounds per square inch.

Air is kept to a minimum. A whole apple would collapse into its center seed cavity, for example, but sliced apple would come out fine.

The process has been proven effective “in killing bacteria such as E. coli, Listeria,” said researcher V.M. Bala at the National Center for Food Safety and Technology near Chicago, where Flow and other corporate partners work with the U.S. Food and Drug Administration and scientists from Illinois Institute of Technology.

And pressurized foods “are much closer to natural-looking, fresh-looking,” Bala noted. Treated orange juice and salsa “look and taste like freshly prepared.”

The next step, and it may be just a few years away from supermarket shelves, is “shelf-stable” food that will keep for months or years without refrigeration.

Researchers believe a combination of pressure and moderate heat--in the 158-degree to 203-degree range--will do the trick.

The Army, which is looking for an alternative to its Meals Ready to Eat, or MREs, is supporting the research.

These meals are expected to taste “just prepared” when they’re heated and served, said Edmund Ting, chief technology officer for Fresher Under Pressure.

High temperatures and irradiation can undermine flavor and nutrition. Freezing and thawing also change foods, and leave some vegetables “kind of limp, kind of tough and chewy. So hopefully this technology will get us to the point it’ll be a lot crisper, a lot more fresh-like,” Ting said.

“People don’t buy food because it’s safe. They buy food because it tastes better,” says Pat Adams, Fresher Under Pressure’s president and CEO.

When high-pressure treatment is used to preserve guacamole by Keller, Texas-based Avomex, “it helps blend the whole product together,” Adams said. “You get a much higher-quality product.”

For oyster processors such as Nisbet Oyster Co. in Bay Center, Wash., and Motivatit in Houma, La., “the safety is almost a secondary benefit,” Ting said. “They’ve been looking for a technology to shuck oysters forever.”

In most cases--for most canned goods, for example--pressure treatment will not replace pasteurization. Its best use at this stage is for higher-value, heat-sensitive foods.

“Not just vitamins, but folic acid, niacin--all of these nutritional components are harmed by heat,” Ting said. After orange juice is conventionally heat-processed, “some of the vitamin C is put back. But some of these things people don’t put back in,” because consumers are unaware of them.

Flow and the center are about midway through a three-year Army-backed project to develop shelf-stable products--MREs of “higher quality and higher nutrient content,” said Patrick Dunne at the Natick Soldier Center in Massachusetts.

MREs now are prepared in giant pressure cookers, where they poach for extended periods at about 250 degrees.

“Right away you can see the potential for overcooking,” Dunne deadpanned.

Army standards for shelf stable are above and beyond civilian ones, he notes. MREs must be storable for up to three years at temperatures around 80 degrees.

Dunne anticipates a marketable shelf-stable product by mid-2005--two years after the center’s three-year project is completed.

The key is eliminating the threat from bacterial spores, which are much tougher than live bacteria.

“That’s why canning”--heat pasteurization--”is such a harsh process. It’s absolutely required to get rid of spores that cause botulism,” said Kathy Knutson, outreach manager at the Chicago-area research center.

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Pressure-Packed Procedures

Solid foods being subjected to high pressure are sealed in a flexible package and placed in a stainless-steel vessel filled with water. Liquids are pumped through specially built systems and bottled later.

The vessel is then filled with water and pressurized by a pump up to 87,000 pounds per square inch. By comparison, water pressure at the deepest part of the ocean is about 15,000 pounds per square inch.

Here are some examples of processing times and pressures:

* Acidic juices are usually pressurized for 60 seconds at 80,000 psi to reduce pathogens such as E. coli.

* Oysters are usually pressurized at 37,000 to 42,000 psi for 40 to 70 seconds to shuck the oyster. Longer hold times--up to three minutes--are used to reduce Vibrio bacteria.

* Ready-to-eat meats are usually pressurized at 87,000 psi for up to two minutes to reduce pathogens such as Listeria monocytogenes.

Fresher Under Pressure’s smallest commercial unit is a 35-liter vessel that can process about 450 pounds per hour. The primary commercial unit is a 215-liter vessel that can process about 1,800 pounds per hour.

The largest available unit is a 320-liter unit that can process about 2,400 pounds per hour. It costs about $2 million.

High-pressure processing is also being researched for medicinal uses, particularly with viruses.

Flow International / Associated Press