1. Food Microbiology

2. What organisms are studied in food microbiology
BACTERIA—*
FUNGI—molds and yeasts *
ALGAE—dinoflagellates/shellfish *
PROTOZOA—amoeba, Giardia *
Viruses—Hepatitis/shellfish
Prions
Helminths—worms
* TRUE microbial cells

3. Genus, Species, Strain and Type
All living organisms have a first name and a second name:
The first name is always capitalized (Genus)
The second name is always denoted in lower case letters
(species)
Both names are always italicized or underlined
Example
Lauren brandon or Lauren brandon
Strain refers to a genetic change made in an organism that makes
it different from the predominant species organism
Type refers to surface changes that make the organisms distinguish
able from others of its species

4. Food Spoilage Fungi— Bread and Cheese Mold
Bacteria— Erwinia caratova soft
rot in carrots and cucumbers
some Yeasts

5. Microbes we can eat
Fungi: Mushrooms are actually a microorganism— although
the fruiting body is macroscopic!!!
Yeasts: Saccharomyces species (Yeast Paste) or dry yeast
Bacteria: Spirulina platensis (a cyanobacterium)
Algae: Chlorella (fresh water), Dunaliella (salt water)

6. Microbes that we can exploit
Bacteria—cheese, yogurt, vinegar, bread and
sauerkraut production (Lactobacillus, leuconostoc, etc)
Yeasts—bread, beer, liqueurs, wine
Molds—cheeses (Aspergillus, Trichoderma etc.,)

7. Bacteria in agriculture
Rhizobium spp: Nitrogen fixation in root nodules of legumes
alfalfa etc.
Bacteria used in engineering produce that is resistant to
adverse environmental conditions, pests pathogens and spoilage

8. Conditions for Spoilage
Water pH
Physical structure
Oxygen
temperature

9. Intrinsic and Extrinsic FactorspH
Moisture Content
Oxidation-reduction Potential
Nutrient Content
Antimicrobial Constituents
Biological Structures
Intrinsic-”parameters of plant and animal tissues that are an inherent part of the tissues…”
Jay, 2000

10. Extrinsic Factors Temperature Relative Humidity
Gases in the Environment
Presence of Other Microorganisms

11. Microorganism Growth in Foods

12. pH Effects of pH Other Environmental Factors
Enzymes
Nutrients
Other Environmental Factors
Temperature
Salt
Age
No known pathogen grows below pH of 4.6
Clostridium botulinum pH
Optimal –
Other considerations
1. Type of Acid
Citric. Hydrochloric, phosphoric, and tartaric acid permit growth at lower pH than acetic or lactic
Yeast and Molds can grow at lower pH.
Acidic Foods-fruits, soft drinks, vinegar,wines
2. Buffering capacity-ability to resist changes in pH
Ie meats have high buffering capacity
pH Effects
2 Aspects
Functioning of Enzymes
Transport of Nutrients
In acidic environments, the cells must keep H+ ions out or pump out H+ ions.
DNA and ATP require neutrality to function
Transport of nutrients
Environmental Factors
Temperature
pH becomes more acid when Temp increases
Salt
Salt can broaden the pH growth range of some mo’s, but when concentration exceeds optimal levels then the growth range can be narrowed
Age
Young cells more susceptible
No pathogen grows below pH of 4.6 – C. bot.
pH <3.5
Citrus fruits, pickles, kiwi, condiments (mayo)
pH 6-7
Meat,milk, corn, vegetables, eggs
Molds and Yeast more tolerant of pH extremes
Molds 0-11
Yeast 1.5 to 8.5

13. Moisture Remove and/or Bind Moisture Water Activity – Aw
Humectants
Dehydration
Water Activity – Aw
Most Fresh Foods - Aw > 0.99
One of the oldest methods of preservation is drying/dessication
Humectants – Salt, sugar, proply glycol
Dehydration – Remove Water/Dry
Water Activity – Amount of Water available for Chemical reactions and microbial growth
ratio of the water vapor pressure to the vapor pressure of pure water at the same temperature
A2 – p/po
P= Vapor pressure of the solution
Po= Vapor pressure of the solvent (water)
Related to Relative Humidity
RH+100 x Aw20
Pure Water Aw=1.00
22% NaCl Solution = 0.86
Saturated NaCl Solution = 0.75
Spoilage Bacteria 0.91
Spoilage Yeasts 0.88
Spoilage Molds .80 1
Pure water
No water

14. Microbial Growth and Aw
Halophilic 0.75
Xerophilic molds 0.61
Osmophilic yeasts 0.61
Lowest Aw for Pathogen Growth
0.86
Stapholococcus aureus
Halophilic – Salt Loving - Vibrio
Xerophilic – Dry Loving
Osmophilic – Survives High Osmotic Pressure
No pathogen survives below 0.86
Stapholococcus aureus survives, but does not grow

16. Composition and pH putrefaction
proteolysis and anaerobic breakdown of proteins, yielding foul-smelling amine compounds
pH impacts make up of microbial community and therefore types of chemical reactions that occur when microbes grow in food

17. Water availability
in general, lower water activity inhibits microbial growth
water activity lowered by:
drying
addition of salt or sugar
osmophilic microorganisms
prefer high osmotic pressure
xerophilic microorganisms
prefer low water activity

18. Antimicrobial substances
coumarins – fruits and vegetables
lysozyme – cow’s milk and eggs
aldehydic and phenolic compounds – herbs and spices
allicin – garlic
polyphenols – green and black teas

19. Microbial Growth and Food Spoilage
results from growth of microbes in food
alters food visibly and in other ways, rendering it unsuitable for consumption
involves predictable succession of microbes
different foods undergo different types of spoilage processes
toxins are sometimes produced
algal toxins may contaminate shellfish and finfish

20. Microbial Growth PhasesD
A=Lag Phase
B=Log/Exponential Phase
C= Stationary Phae
D= Death Phase B
Log10 cfu/g
Growth Curves
Plotted on log paper
Log10 of Count vs. Time
A-Lag. Increase Lag Phase to Prevent Food Spoilage. Microorganisms adjusting to new environment
B-Log.
C-Stationary. Build up of toxic materials and other factors.
D-Death Phase
1 x 10^9 is maximum growth of most microorganisms A
Time

21. Food-Borne Illness ERS Estimates CDC Estimates
$6.9 Billion/Year Cost of FBI
CDC Estimates
76 Million Cases of FBI Annually
325,000 Hospitalizations
5,000 Deaths

22. What Organism Causes the Most Cases of Food-Borne Illness Annually?
Campylobacter
Campylobacter

23. What Organism Causes the Most Deaths Due to Food-Borne Illness?
Salmonella
Salmonella

24. Agents of Disease (Foodbourne Pathogens)
BACTERIA E coli O157:H7, Salmonella spp., Vibrio cholera,
Bacillus cereus, Clostridium botulinum, Listeria monocytogenes,
Staphylococcus aureus
VIRUSES Enteroviruses, Norwalk virus, Hepatitis virus
PRIONS Mad Cow Disease (BSE) and Creutzfeldt-Jakob Disease
PROTOZOA Giardia lamblia, Cryptosporidium parvum, Entamoeba
histolyticum, Cyclospora cayetanesis
HELMINTHS Tapeworms (Beef, Fish and Pork), Flukes (Fish and
Shellfish), Roundworms and Hookworms

26. Food-Borne Intoxications
ingestion of toxins in foods in which microbes have grown
include staphylococcal food poisoning, botulism, Clostridium perfringens food poisoning, and Bacillus cereus food poisoning

27. Toxins ergotism aflatoxins fumonisins
toxic condition caused by growth of a fungus in grains
aflatoxins
carcinogens produced in fungus-infected grains and nut products
fumonisins
carcinogens produced in fungus-infected corn

29. Presence of Other Microorganisms
Competitive Exclusion
General microbial antagonism
Lactic Antagonism
Some food-borne organisms produce substances that are inhibitory or lethal to other organisms
antibiotics, bacteriocins, hydrogen peroxide, organic acids
Sterile foods more susceptable to contamination and uncontrolled growth

30. Hurdle Concept
Combine Intrinsic and Extrinsic Factors to Control Microbial Growth
Combination requires less severe treatments to foods to get desired inhibition