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Let’s Talk Science
POTENTIALLY HAZARDOUS
FOODS
What is a potentially hazardous food?
A potentially hazardous food is a food that is
natural or man made and is in a form capable
of supporting the rapid and progressive
growth of infectious and toxin-producing
microorganisms.
These foods typically have:
¾¾High protein or carbohydrate content
¾¾High moisture content
¾¾Low acidity
PROTEIN AND CARBOHYDRATE
Protein is a nutrient necessary for a variety of
processes in the human body. Like humans,
bacteria need protein to grow and multiply.
Meat, poultry, fish, seafood, eggs, beans, peas,
nuts and dairy foods have a high protein
content.
Carbohydrate is a nutrient primarily responsible
for providing energy to all cells of the body.
Bacteria also need carbohydrate for energy.
Bread and other grain foods, dairy foods, fruits
and vegetables can have a high carbohydrate
content.
WATER
Bacteria need a percentage of moisture or
“water by volume” in a food for growth. There
must be enough available water to support
growth. This is expressed as water activity (a
measure of water bound to food that is not
available for bacteria growth). Water activity
is measured on a scale from 0-1.0. Disease
causing bacteria grown in foods that have a
water activity higher than .85.
ACIDITY
The acidity of foods is expressed as pH. The pH
of a food is measured on a scale that ranges
from 0 to 14. Most foods considered “acidic”
have a pH less than 7.0. Foods with a pH less
than 4.6 do not normally support the growth of
disease-causing bacteria. Most bacteria prefer
a neutral environment near a pH of 7.0, but can
grow in a range of 4.6 to 9.0. Milk, meat and
fish are in this range.
What Do You Think?
Which food would have a lower water activity,
fresh chicken or frozen chicken? The answer is fresh
chicken with water activity at about .98. The water
activity of frozen chicken is zero. Even though
both are about 60% water by volume, the water
in the frozen chicken is not available to bacteria
for growth. Freezing slows
the growth of bacteria
to preserve food for long
periods.
Time and Temperature
Many bacteria grow in a temperature range
between 40 and 1400 F. Under ideal conditions,
bacterial cells can double in number every
15 to 30 minutes. Some double more quickly.
Bacteria are single-celled microorganims that
reproduce by binary fission. In this process,
the cell divides into two identical daughter
cells with identical DNA to the parent cell. Each
daughter cell divides into two more cells. Over
the course of just 7 hours, it is possible that
one bacterium, such as Escherichia coli, could
generate over two million bacteria! Exactly how
many can make you sick depends on the kind
of bacteria. For some, it only takes a few cells to
cause foodborne illness.
Examples of Potentially
Hazardous Foods
Meats
Poultry
Eggs
Fish
Shellfish
Dairy products
Cooked vegetables
Cooked rice
Cooked pasta
Cooked beans, peas and
lentils
Cut fruits and vegetables
Raw seed sprouts
Cooked soybean products
(such as Tofu)
Garlic-in oil or other
vegetable-in-oil mixtures
(unless they have been
treated to prevent
growth of Clostridium
botulinum)
Cooked cereal
Prepared by: Janie Burney, PhD, RD,
Professor, Family and Consumer Sciences
Keep Hot Foods Hot
and Cold Foods Cold
The term “potentially hazardous foods” is
used by the Food and Drug Adminsitration
in the FDA Food Code. The Food Code is a
model law that helps government entities,
such as health departments, regulate retail
and food service industries to protect the
health of consumers. The principles of
time and temperature also
apply to foods you handle
at home.
It is important that you
do not leave potentially
hazardous foods at room
temperature for more
than two hours, or no
more than one hour if
the temperature is above 900F.