2.basic food microbiology
TRANSCRIPT
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Basic FoodMicrobiology
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Why do we need to identify
bacteria in food ?
Safeguardhuman health
Prevent spoilageof food
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Introduction of Microorganism
Microbiology is a specialized
area of biology that deals livingthings that are too small to beseen with naked eyes
The too small organisms are
called microorganism ormicrobes
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Introduction of Microorganism (cont..)
Microorganisms are tiny, mostly one-celled organisms capable of rapidreproduction under proper growthconditions.
Bacteria, viruses, yeasts, molds, andprotozoans.
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Food preservation
Food spoilageFood poisoning
Food legislation
Evolution of Food Microbiology
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Microbes
Bacteria
Fungi
Molds
Yeast
Parasites
Viruses
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Bacteria (cont..)
The Size and Shape Extremely small
Vary in size
0.1m to 5m Vary in Shape
Coccus
Bacillus
Spirilla
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Bacteria (cont)
Effects on food
They can cause spoilage;
They can cause food borne illness;
They can transform a food properties in
a beneficial wayfood fermentation
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Spoilage and Disease Causing
Bacteria
Spoilage Bacteria
Degrade food
Reduce quality of food tounacceptable levels
Pathogenic Bacteria
Diseasecausing
microorganisms
Foodborne illness
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Fungi The fungi
(singularfungus) are akingdom ofeukaryotic
organisms. Use organic
chemicals forenergy
Yeasts, molds,and mushroomsare examples offungi.
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Molds
Molds are the most typical forms of fungus
Molds are ubiquitous and essential decomposers oforganic substances
The myceliumis made from strings of hyphae,which makes the body that we see
Molds reproduce via spores
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Yeast
Yeasts are unicellular, eukaryotic microorganismsclassified in the kingdom Fungi
Reproduce by budding The yeast species Saccharomyces cerevisiaehas
been used in baking and fermenting alcoholicbeverages for thousands of years.
Able to grow in low pH, (5.5 or lower), thepresence of sugars, organic acids and other easilymetabolized carbon sources
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Yeast (cont..)
This causes the physical, chemical, andsensory properties of a food to change,
and the food is spoilt The growth of yeast within food products
is often seen on thier surface, as incheeses or meats, or by the fermentation
of sugars in beverages, such as juices,and semi-liquid products, such as syrupsand jams
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Eukaryote vs Prokaryotes
Eukaryote
an organism with a complex cell or cells, in which thegenetic material is organized into a membrane-bound
nucleus or nuclei. Comprise animals, plants, and fungiwhich are mostly
multicellularas well as various other groups that arecollectively classified as protists (many of which areunicellular).
Prokaryotes
organisms, such as bacteria and archaea, that lacknuclei and other complex cell structures.
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Parasites (cont)
How are they transmitted? through consumption of contaminated food and water, or by
putting anything into your mouth that has touched the stool(feces) of an infected person or animal.
How do they vary? different types and range in size from tiny, single-celled,
microscopic organisms (protozoa) to larger, multi-cellularworms (helminths) that may be seen without a microscope.
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Viruses
Virusesare extremely small parasites.
They require living cells of plants, animals,
or bacteria for growth. The virus is mainly a packet of genetic
material which must be reproduced by the
host.
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Viruses
Outside a cell, a virus can't reproduce itself;but once a virus invades a living cell, it
turns that cell into a virus factory. In time,thousands of new viruses burst out and goon to invade other cells.
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Microbial Growth
Growth an increase in the number of cells, not an
increase in size
Generation growth by binary fission
Generation time
time it takes for a cell to divide and thepopulation to double; most are 1-3 hours (E.coli:every 20 min.)
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Bacterial Growth Curve
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Bacteria Growth
LAG PHASE: Growth is slow at first, while the "bugs" acclimate to the food
and nutrients in their new habitat.
LOG PHASE:
Once the metabolic machinery is running, they start multiplyingexponentially, doubling in number every few minutes.
STATIONARY PHASE: As more and more bugs are competing for dwindling food and
nutrients, booming growth stops and the number of bacteriastabilizes.
DEATH PHASE: Toxic waste products build up, food is depleted and the bugs
begin to die.
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Factors Affecting Microbial
Growth in Foods
There are six main factors that affectmicrobial growth in food:
F-A-T-T-O-M
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A (Acid--pH of the food)
Remember the pH scale? Whats the pHrange of acids?
At what pH do you think microorganisms
grow best? Organic acids are often added to foods to
lower the pH Can you think of an example?
If we lower the pH of a food,microorganisms may still grow, but theygrow much slower
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Temperature and Time
What is refrigeration temperature?
In the refrigerator:Do pathogens grow?
Do spoilage microbes grow?
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Food with vegetative cellsand some spore cells
Only spores survive when food isheated (cooked) to 165 F and then
held >140F
Spores can becomevegetative cells again if
food is not cooled properly
Vegetative cells grow tohigh numbers and some
produce toxins
Spore
Vegetative
Cell
Growth
Toxin
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Temperature and Time (cont.)
If food is held on a hot serving line (>140F), pathogens can NOT grow
Most bacterial pathogens need time togrow to high enough levels or produceenough toxin to cause disease (4 hrs inthe danger zone)
One of the most common factors leadingto foodborne illness is improper coolingof leftover foods! Where do foods cool faster--on the counter or in
K h t
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41F
140F
Danger
Zone
Keep coldfoods cold
Keep hotfoods hot
Food Safety
Thermometer
Temperature
range of rapid
pathogen growth
=
DangerZone
Hot
Cold
O
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Oxygen(Oxidation-Reduction Potential)
Generally refers to the amount of Oxygenpresent
Most bacterial pathogens can grow with or
without Oxygen HOWEVER, some food pathogens can only
grow when no Oxygen is present (e.g.,Clostridium botulinum)
Many spoilage bacteria and molds requireOxygen to grow
So, why do some foods get vacuum
packaged (no oxygen)? Does it make the
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Moisture (cont.)
Water Activity (AW) A measure of the FREE WATER--water
that is available for microbial growth
AW can range from: 0.00 (no free water) to 1.00 (all free water)
We dont measure AW values in the Air
Force, but you can look them up in foodmicrobiology books
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Aw Foods (some examples)
0.98 to 1.00 Fresh meats, fruit, vegetables, canned fruit inlight syrup, canned vegetables, beverages
0.93 to 0.98 Processed cheese, bread dough, lightly saltedmeats (e.g., hot dogs), canned fruit in heavy
syrup0.85 to 0.93 Ham, aged cheddar cheese, most bread, dry
sausage, sweetened condensed milk
0.60 to 0.85 Flour, cereals, jams/jellies, nuts, some cheese,heavily salted foods, dried fruit
< 0.60 Chocolate, honey, noodles, crackers, potatochips, dried milk, dried vegetables
*Pathogens do not grow or produce toxins
at AW< 0.85Adapted from APHA, Compendium of Methods for the Microbial Examination of Foods, 1992.
*
Potentially Hazardous Foods
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Potentially Hazardous Foods(PHF)
Definition: A food that supports growth ofinfectious or toxin-producing microorganisms
So these are the foods that have all the FATTOM requirements for pathogen growth that we
just discussed
Examples of PHFs: Raw or cooked foods of animal origin:
Meat, Poultry, Waterfoods, Eggs, Dairy Products Some fruit and vegetables
Could a non-PHF cause a foodborne illness?
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Fruit &Vegetables (cont.)
Which F&V are PHFs? Cut melons (like cantaloupe)
If intact, bacteria dont grow on outer surface But, when cut, bacteria are dragged over cut surface
And the pH of some melons is >4.6
Heated/cooked fruits and vegetables
Rice, beans, baked potatoes, etc. after they are cooked
Seed sprouts (such as alfalfa sprouts)
Garlic in oil mixtures
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What do you think about
the safety of lettuce?
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Summary
5 main classes of microorganisms with whichthe foodservice manager is concerned
The greatest menace to food bacteria Viruses can multiply only in living cells
Mold and yeast growth occurs commonly oncertain foods