High pressure to kill foodborne germs
about 37,000 pounds per square inch - to kill germs that may damage
food or cause illness.
Scientists are using water under very high pressure - starting at about 37,000 pounds per square inch - to kill germs that may damage food or cause illness.
An Associated Press report cites the advent of this new high-pressure processing as just one of the new technologies emerging to tackle the challenge of food safety.
The new process, pioneered by Fresher Under Pressure, a subsidiary of US company Flow International, uses stainless-steel processors and ultra high pressure to squeeze the germs - but not the colour, flavour, texture or nutrients - out of guacamole, salsa, avocado slices, charcuterie meats, juices and raw oysters.
Foods are simply placed inside the device - liquids are pumped through - and pressure applied, for the maximum of a few minutes.
According to the story, 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 centre seed cavity, for example, but sliced apple would come out fine.
The process has proven effective "in killing bacteria such as E. coli and 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 US Food and Drug Administration and scientists from Illinois Institute of Technology. Pressurised foods "are much closer to natural looking, fresh-looking foods", Bala noted.
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 US 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 are heated and served, said Edmund Ting, chief technology officer for Fresher Under Pressure.
In most cases - for most canned goods, for example - pressure treatment will not replace pasteurisation. 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.
Flow and the centre are almost halfway 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.
Dunne anticipates a marketable shelf-stable product by mid-2005 - two years after the centre'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 pasteurisation) 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 centre.
Solid foods 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 pressurised 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.
Acidic juices are usually pressurised for 60 seconds at 80,000 psi to reduce pathogens such as E. coli. Oysters are usually pressurised 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 pressurised 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-litre vessel that can process about 450 pounds per hour. The primary commercial unit is a 215-litre vessel that can process about 1,800 pounds per hour. The largest available unit is a 320-litre unit that can process about 2,400 pounds per hour.
High pressure to kill dangerous bacteria will certainly court far less controversy than irradiation, viewed with suspicion and distrust by the consumer, particularly in Europe.
