2.Basic Food Microbiology

8/3/2019 2.Basic Food Microbiology

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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

2.Basic Food Microbiology

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