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List of Terms: U-V-W
(Return to Comprehensive List of Terms)
> Ultra High Pressure (UHP) Treatment
A new process used at the processing stage that utilizes very high pressure to
kill bacteria in foods.
Photo: Flow International Corporation
Today, some food producers are using a new method called Ultra
High Pressure (UHP) Treatment to kill harmful bacteria in foods.
Food Safety Implication: Ultra High Pressure destroys bacteria, but
does so using pressure, rather than high temperatures or chemical additives. Thus,
foods, such as juices, salsas, cold cuts, and other moist foods, are made safer
without affecting the vitamins and flavor.
How It Works: Using specially-designed equipment, packaged food is exposed
to 50,000 to 100,000 psi (pounds per square inch) of pressure for a short time.
The ultra high pressure interferes with the metabolism and structure of bacteria
and destroys these living cells, but does not crush the food.
As long as the food is mostly air-free and contains water, hydrostatic pressure
doesn't crush food because the water in the food protects it from physical damage.
However, living bacteria are destroyed by the effects of high pressure on their
cellular functions.
> U.S. Department of Agriculture (USDA)
A department of the United States government that has many varied responsibilities,
including food safety. The primary agency in USDA responsible for food safety
is the Food Safety and Inspection Service. (See Food
Safety and Inspection
Service.)
> "Use By" Date
This is the last date a consumer is recommended to use a product while it is at
peak quality. This date is recommended for best flavor or quality. It is not a
"sell by" or food safety date. (Also see "Best
If Used By," Expiration, and
"Sell By" Dates.)
> Vacuum Packaging (see Packaging)
> Vibrio cholerae
This bacterium occurs naturally in the aquatic and marine environment. It causes
cholera, a severe disease that, if untreated, could cause death.
Vibrio cholerae
Sources: Raw and undercooked seafood or other contaminated food and
water. The contamination is the result of the food or drinking water mixing with
water from sources that receive the untreated feces of cholera victims.
Illness
Incubation: 6 hours to 5 days after eating contaminated food.
Symptoms: They are often absent or mild. Some people develop a severe
illness with profuse diarrhea, vomiting, and leg cramps. Loss of body fluids can
lead to dehydration and shock. Without treatment, death can occur within hours.
Duration: 7 days.
> Vibrio vulnificus
A bacterium that is in the same family as those that cause cholera. It normally
lives in warm seawater and is part of a group of vibrios that are called "halophilic"
because they require salt.
Vibrio vulnificus can cause infection in people who eat raw, contaminated
seafood, often shellfish, or have an open wound that is exposed to seawater. It is a rare cause
of disease, but it is also underreported.
Vibrio vulnificus
Sources: Raw fish and shellfish, especially raw oysters.
Illness
Incubation: Usually within 16 hours of ingestion or exposure to organism.
Symptoms: Diarrhea, abdominal pain, nausea, vomiting, fever, and sudden
chills. Some victims develop sores on their legs that resemble blisters.
Duration: 2 to 3 days.
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Human viruses cannot grow in foods. Since viruses are very host-specific,
a human virus will rarely multiply even in foods that are still alive (like oysters).
However, they can persist for a long time. |
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Is it true that some viruses are resistant to heat and cold? If so, what
food safety precautions should consumers take?
Foodborne viruses are not especially resistant to heat. Most virus outbreaks
are the result of foods that are not cooked, or are contaminated after cooking.
Many viruses are very stable in the environment, but cooking is good at denaturing
the proteins that protect the virus. That's why it's important to cook food, including
seafood, thoroughly before eating it.
On the other hand, it's true that viruses are resistant to cold. Chilling or
freezing does not eliminate viruses. Good agricultural and manufacturing practices
along the farm-to-table continuum are needed to keep food from being contaminated
by pathogens in the first place.
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> Virus
A non-cellular particle that consists minimally of protein or nucleic acid
(DNA or RNA). In order to survive, it must replicate inside another cell, such
as a bacterium or a plant and animal cell. (Also see Noroviruses.)
Photo: F.P. Walker, U.S. EPA
The Norwalk Virus is a potent
norovirus that is rapidly gaining
groud as a public health threat.
Food Safety Implication: Food serves as a transportation device to get
viruses from one host to another. Once the contaminated food is eaten, a virus
can multiply in living cells and cause foodborne illness in humans. Food can become
contaminated with viruses in a number of ways, such as:
- A Food Handler - who picks, processes, prepares, or serves food and
is shedding (excreting the virus in their stool). If the person practices poor
hygiene, he or she may transfer the virus to food.
- Contaminated Water - used to irrigate or wash foods.
- Seafood - grown or collected from contaminated water and in which
viruses have colonized. Foods such as oysters, which pump a lot of water each
day through their bodies and filter out microorganisms, are very likely to collect
viruses from the water.
- Cross-Contamination - of safe food by contaminated food (or liquids
dripping from such foods). For example, raw seafood juices that come in contact
with fresh fruits or vegetables. Sometimes, this phenomenon makes it more difficult
to pinpoint the actual food involved in a foodborne outbreak.
What's the difference between viruses and bacteria?
The differences between viruses and bacteria are numerous. Viruses are the
smallest and simplest life form known. They are 10 to 100 times smaller than bacteria.
The biggest difference between viruses and bacteria is that viruses must have
a living host - like a plant or animal - to multiply, while most bacteria can
grow on non-living surfaces.
Also, unlike bacteria, which attack the body like soldiers mounting a pitched
battle, viruses are guerilla fighters. They don't attack so much as infiltrate.
They literally invade human cells and turn the cell's genetic material from its
normal function to producing the virus itself.
In addition, bacteria carry all the machinery needed for their growth and multiplication,
while viruses carry mainly information - for example, DNA or RNA, packaged in
a protein and/or membranous coat. Viruses harness the host cell's machinery to
reproduce. In a sense, viruses are not truly living," but are essentially information
(DNA or RNA) that float around until they encounter a suitable living host.
Why are shellfish and salads especially friendly to viruses?
Shellfish are especially friendly to viruses because shellfish pump water
through their bodies and thus, concentrate food and contaminants, such as viruses,
from the water. Once the virus is on or in the shellfish - a live host - it may
persist for a longer time than if it were suspended in the water. Some shellfish
are eaten raw or lightly cooked, which increases the risk of foodborne illness.
Produce used for salads, lettuce, spinach, etc., grow low to the ground where
they are more likely to come in contact with contaminated, organic fertilizers,
such as manure. Also, sometimes produce is irrigated with contaminated waters
or picked by farm workers with poor hygiene practices. The complex, multi-layered
surfaces of salad produce are more difficult to clean after picking than, for
example, the surface of an apple or potato. Finally, because salads are usually
eaten raw, there is no heating step that would inactivate the viruses
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How It Causes Disease: Viruses cause disease in humans by tricking healthy
cells into duplicating the virus's nucleic acid instead of its own, which lets
the virus multiply. Once the virus is duplicated, the healthy cell usually dies.
Some Examples of Foodborne Viruses:
- Norovirus, previously Norwalk virus and other Norwalk-like viruses
- Hepatitis A
- Rotavirus (mainly affects young children)
Some Examples of Human Viruses:
- Influenza (causes the flu)
- HIV (causes AIDS)
- Polio (causes poliomyelitis)
- Rhinovirus (causes colds)
- Rubella (causes German measles)
> Water Activity (aw)
The amount of water that's available to support bacterial growth in different
foods.
Food Safety Implication: Bacteria require a certain amount of "free"
water in order to grow. The more available water, the faster the bacteria will
grow. Bacteria, yeast, and mold multiply rapidly at a high water activity - above
0.86. Meat, produce, and soft cheeses have water activity between 0.86 and 1.0,
and thus support rapid bacterial growth.
How It Works: Water activity is measured on a scale of 0 to 1.0 and
is derived from a measurement of the amount of moisture in a food product and
the amount of solutes (a dissolved substance). The greater the solutes in a specific
amount of moisture, the lower the water activity.
Water activity is lowered by the addition of solutes, such as salt or sugar.
These food constituents bind water molecules together, making it unavailable for
use by micro-organisms. Preservation methods that use large amounts of salts or
sugars work by reducing the water activity.
> Water Quality
The nature or state of water for consumption or use on foods along the farm-to-table
continuum.
The nature or state of water for consumption or use on foods along the farm-to-table
continuum.
Food Safety Implication: Along the farm-to-table continuum, water quality
dictates the potential for pathogen contamination. For example, at the farm, growers
use good agricultural practices (GAPs) to minimize the risk of contaminated water
being used on the produce. At processing facilities, good manufacturing practices
(GMPs) are followed to minimize microbial contamination from water used during
processing. (Also see Good Agricultural Practices and Good
Manufacturing Practices.)
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