Microbes
Objectives
Describe how different
microbes cause food
spoilage.
Describe methods used in
controlling food
contamination.
Explain the methods used in
preventing the growth of
microbes in food.
Explain methods for
decreasing food
contamination
Microbes and Spoiled Food
Food Microbiology
Food microbiology is the study of
certain microbes and how they
affect food.
Microorganisms
Can Alter the flavor, color, or
odor of food.
Fruits and vegetables are still
living before you eat them
Ripening May occur after
harvest, as well as well as
browning and softening
The natural fate of plant
material after it dies is
degradation by microbial
action.
Molds
Are a Fungus
Molds
organisms that receive their
nutrients from decaying
organisms and can live almost
anywhere where air and
moisture are present.
Molds produce spores which
can be carried through the air.
Spores can grow on substances
with favorable characteristics
for temperature, moisture, and
nutrients
Benefits and Detractors
of Molds
Used to add flavor and color
to cheese
making soy sauces, citric
acid, lactic acid, and many
enzymes.
Penicillin and other
antibiotics are produced
with the help of molds.
Can also produce
mycotoxins which are
poisons and are a byproduct of mold growth.
Mold Growth Temperatures
Mesophiles grow at room
temperature (50° F–110° F).
Psychrophiles grow at
refrigerated temperatures
(less than 50° F).
Thermophiles grow at high
temperatures (110° F–140° F).
Molds require oxygen in order
to survive
Yeasts
members of the fungi
family.
Does not contain
chlorophyll.
Live mainly on sugars and
starches or in high salt or
sugar environments
Used to aid the
fermentation process.
making bread, beer, and
yogurt
Bacteria
Most adaptable of all
microbes
Bacteria associated with
food spoilage are
heterotrophic
Can get nutrients from
almost anything
Bacteria
Some bacteria under
favorable conditions can
reproduce every 20
minutes.
One cell can reproduce
17 million in only 8
hours.
Bacteria can also be
classified as
psychrophilic, mosphilic
or thermophilic. Bacteria
die at a temp of 180°F.
dormant spores can live
indefinitely at this
temperature.
Viruses
Among the smallest
forms of life.
Must be viewed with an
electron microscope.
All viruses are
parasites.
lives off the genetic
material of another
organism.
Controlling
Contamination
Contamination
the process of a food item
becoming unfit for
consumption due to contact
with an unclean organism.
Preventing contamination
involves controlling four
conditions
Relate to both the
ingredients t and the
environment where
processed.
Controlling Air
Movement
Molds, yeasts, and bacteria
travel through the air.
If the movement of air is
controlled, the chances for
contamination are
minimized.
This is one reason why
large food processing
machines are covered with
lids.
Segregation
When foods are processed, each
step is separated so that the
contaminant does not travel from
one step to the other.
Segregation is routine in food
processing plants.
Most people are not as careful at
home. The same cutting board may
be used to cut different foods
without being washed.
Temp Control
Most food contaminants are
mesophiles
grow at room temperature.
Food is rarely kept at room
temperature for extended lengths
of time.
Meat should be kept refrigerated
before it is cooked.
After it is cooked, it should not be
left at room temperature for long.
Foods should be kept below 40°F
or above 140°F to prevent bacterial
growth.
Moisture Control
Most microbes thrive in
high-moisture
environments.
High moisture
environments are common
at room temperature.
This is why food spoils less
quickly when heated or
cooled.
Controlling Microbe
Growth
Secondary to preventing
contamination.
Effective prevention of
contaminants makes the
prevention of microbe
growth easier.
Microbe growth
prevention is carried out
using one of two methods.
Controlling Microbe
Growth
Death
can be attained using heat or by
cooling.
halts the physiological
deterioration and microbial action
that occurs in fresh fruits and
vegetables.
Heat is the most effective and
least expensive method of
killing the microbes.
Refrigeration destroys most of
the microbes.
Freezing
Death
Extensive cell damage is created,
which allows deteriorative
enzymes to act rapidly upon
thawing.
Blanching (treating with water at
140 to 150° F) inactivates these
enzymes and preserves the quality
of the product when thawed.
Rapid cooling after blanching
prevents the loss of
carbohydrates, vitamins, and
minerals during the blanching
process.
Fruit that is frozen may also be
treated with ascorbic acid to
retard oxidative processes.
Inhibition
Preventing the growth of
the microbes.
Involves altering the
environment of the
microbes so that they
cannot thrive.
The environment may be
altered by reducing
moisture, adding
chemicals or changing the
pH level of the food.
Inhibition
Food additives
Substances added to foods
during processing to retain
or improve desirable
qualities or characteristics.
Examples
Sulfur dioxide
Potassium sorbate
Sodium propionate
Sodium benzoate
Processing Methods
Can be used to control
microbial growth.
Foods can be
Frozen
destroying enzymes and
microorganisms
Dried
to decrease moisture levels
Processing methods
Canned
Heated to high
temperatures under
pressure
inactivates enzymes but
also kills spoilage bacteria.
High acid foods (fruits)
require less heating
during canning, since high
acidity tends to reduce
spores of anaerobic
Tips for Consumers
Controlling food pathogens
should be a high priority for
anyone that handles food.
Tips to decrease or control food
pathogens include:
Wash your hands and any
surface that food comes in
contact with regularly.
Cold foods should be kept at
temperatures less than 40°F
Hot foods should be kept
above 140°F
Cooked and raw food should
always be kept separate. Keep
utensils and dishes separate as
well.
Tips for Consumers
Meats should never be thawed on
the counter. Use the refrigerator
or microwave to thaw them.
Cooking should not be
interrupted.
Vegetables and fruits should be
washed before consumption.
Discard anything that looks
suspicious
As a general rule, foods should
not be left out for more than 2
hours.
Do not use foods that have
passed their expiration date.
Summary
Think of your kitchen at home, list 4
things in your kitchen that can cause
possible microbial growth.
What is the Use for Food Additives?
What are the 4 major factors that you
must control to prevent microbial
growth?
Create a Venn Diagram comparing and
contrasting yeasts, viruses and bacteria