Basic Food Microbiology
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Why do we need to identify bacteria in food ?
Safeguard human health Prevent spoilage of food
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Introduction of Microorganism
Microbiology is a specialized
area of biology that deals living things that are too small to be seen with naked eyes The too small organisms are called microorganism or microbes
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Introduction of Microorganism (cont..)
Microorganisms are tiny, mostly one-
celled organisms capable of rapid reproduction under proper growth conditions. Bacteria, viruses, yeasts, molds, and protozoans.
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Evolution of Food Microbiology
Food preservation
Food spoilage
Food poisoning
Food legislation
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Microbes
Bacteria
Fungi Molds Yeast Parasites Viruses
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Bacteria
Most important biological foodborne hazards Exist in vegetative cell
Grow, reproduced and produces waste
Some - Sporeformer
Spore thick wall formation within the bacterial cell
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Capable of becoming a vegetative cell Resistant to heat, cold and chemical May survive some cooking temperature Helps survival in the extreme environment Not able to grow or reproduce
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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 way food fermentation
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Spoilage and Disease Causing Bacteria
Spoilage Bacteria Degrade food Reduce quality of food to unacceptable levels Pathogenic Bacteria Disease causing microorganisms Foodborne illness
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Fungi
The fungi (singular fungus) are a kingdom of eukaryotic organisms.
Use organic chemicals for energy
Yeasts, molds, and mushrooms are examples of fungi.
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Molds
Molds are the most typical forms of fungus Molds are ubiquitous and essential decomposers of organic substances The mycelium is made from strings of hyphae, which makes the body that we see Molds reproduce via spores
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Mold Characteristics
Some molds germinate in four-to-twelve hours Left undisturbed, mold can grow and spread in 24-72 hours Floods, leaking pipes, leaking windows, leaking roofs, humidity, spoiled food, and poor housekeeping can lead to mold growth and infestation Molds can hide away until the right conditions cause germination and growth Some molds produce toxic mycotoxins All molds, under the proper conditions, are capable of eliciting a negative health response in humans
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Yeast
Yeasts are unicellular, eukaryotic microorganisms classified in the kingdom Fungi Reproduce by budding The yeast species Saccharomyces cerevisiae has been used in baking and fermenting alcoholic beverages for thousands of years. Able to grow in low pH, (5.5 or lower), the presence of sugars, organic acids and other easily metabolized carbon sources
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Yeast (cont..)
This causes the physical, chemical, and sensory 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 in cheeses or meats, or by the fermentation of sugars in beverages, such as juices, and semi-liquid products, such as syrups and jams
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Eukaryote vs Prokaryotes
Eukaryote
an organism with a complex cell or cells, in which the genetic material is organized into a membrane-bound nucleus or nuclei. Comprise animals, plants, and fungiwhich are mostly multicellularas well as various other groups that are collectively classified as protists (many of which are unicellular).
Prokaryotes
organisms, such as bacteria and archaea, that lack nuclei and other complex cell structures.
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Parasites
What are
Organisms that derive nourishment and protection from other living organisms known as hosts. Several parasites have emerged as significant causes of foodborne and waterborne disease. Live and reproduce within the tissues and organs of infected human and animal hosts, and are often excreted in feces.
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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-cellular worms (helminths) that may be seen without a microscope.
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Viruses
Viruses are 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 go on to invade other cells.
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Microbial Growth
Growth
an increase in the number of cells, not an increase in size growth by binary fission time it takes for a cell to divide and the population to double; most are 1-3 hours (E.coli: every 20 min.)
Generation
Generation time
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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. Once the metabolic machinery is running, they start multiplying exponentially, doubling in number every few minutes. As more and more bugs are competing for dwindling food and nutrients, booming growth stops and the number of bacteria stabilizes.
LOG PHASE:
STATIONARY PHASE:
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 affect microbial growth in food:
F-A-T-T-O-M
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F (Food for the microbes to eat)
Nutrients in food affect microbial growth: Sources of energy (e.g., sugars, proteins) Sources of nitrogen (e.g., proteins) Vitamins Minerals In order for bacteria to grow, the food has to have the right nutrients for the bacteria
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A (Acid--pH of the food)
Remember the pH scale? Whats the pH range 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 they grow much slower
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Acid (cont..)
Most pathogens do not grow at pH < 4.6 Some yeast and molds can grow down to pH 1.5 So What?
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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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Temperature and Time (cont.)
Heating/cooking foods (to an internal temperature of 165F), kills most pathogens
What is not destroyed/killed by cooking?
(Remember the food pathogens lecture?)
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Food with vegetative cells and some spore cells
Only spores survive when food is heated (cooked) to 165 F and then held >140F Spores can become vegetative cells again if food is not cooled properly Vegetative cells grow to high 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 to grow to high enough levels or produce enough toxin to cause disease (4 hrs in the danger zone) One of the most common factors leading to foodborne illness is improper cooling of leftover foods!
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Where do foods cool faster--on the counter or in
Food Safety Thermometer
Keep hot foods hot
140F
Danger Zone
Hot
Danger = Zone
Temperature range of rapid pathogen growth
41F
Keep cold foods cold
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Cold
Oxygen (Oxidation-Reduction Potential)
Generally refers to the amount of Oxygen present
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 require Oxygen to grow
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So, why do some foods get vacuum packaged (no oxygen)? Does it make the
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Moisture (water)
Why is water important to bacteria?
To survive? To grow?
Water in food is present in two forms:
BOUND FREE
Bound water is unavailable for bacteria to grow
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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 food microbiology books
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Aw
Foods (some examples)
0.98 to 1.00 Fresh meats, fruit, vegetables, canned fruit in light syrup, canned vegetables, beverages 0.93 to 0.98 Processed cheese, bread dough, lightly salted meats (e.g., hot dogs), canned fruit in heavy syrup 0.85 to 0.93 Ham, aged cheddar cheese, most bread, dry sausage, sweetened condensed milk
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0.60 to 0.85 Flour, cereals, jams/jellies, nuts, some cheese, heavily salted foods, dried fruit < 0.60 Chocolate, honey, noodles, crackers, potato chips, dried milk, dried vegetables
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*Pathogens do not grow or produce toxins at AW < 0.85
Adapted from APHA, Compendium of Methods for the Microbial Examination of Foods, 1992.
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Potentially Hazardous Foods (PHF)
Definition: A food that supports growth of infectious or toxin-producing microorganisms
So these are the foods that have all the FAT TOM requirements for pathogen growth that we just discussed
Raw or cooked foods of animal origin:
Examples of PHFs:
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 Rice, beans, baked potatoes, etc. after they are cooked
Heated/cooked fruits and vegetables
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 which the foodservice manager is concerned The greatest menace to food bacteria Viruses can multiply only in living cells Mold and yeast growth occurs commonly on certain foods
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