Extrinsic and Intrinsic Factors

Mesophiles

"love ambient" optimum 30-40 Adapted to vertebrate animals (body temp). Minimum growth temp: 7 (cannot grow in fridge) Maximum growth temp: 60 Most foodborne pathogens are mesophiles. Examples: Escherichia coli and Staphylococcus aureus

Psychrophiles

"love cold" optimum 0-15 Adapted to cold environments (cold water fish) but not common in foods

Hyperthermophiles

"love very warm" Optimum greater than 80 Not relevant in foods

Thermophiles

"love warm" optimum greater than 45 Relevant for spoilage in tropical climates. Examples: Geobacillus stearothermophilus

Psychrotrophs

"tolerate cold" optimum 4-25 Adapted to "ambient" temperature in environment. They can grow in the fridge; responsible for spoilage of refrigerated foods. Examples: Listeria monocytogenes (pathogen) and Pseudomonas spp. (spoilage)

How is water activity decreased?

1. Drying 2. Dry salting 3. Brining (osmotic dehydration)

What are the extrinsic factors?

1. Temperature 2. Presence and concentration of gases 3. Relative humidity

What are the intrinsic factors?

1. pH 2. Moisture (aw) 3. Oxidation - Reduction Potential (Eh) 4. Contents of nutrients or antimicrobial constituents 5. Physical structures

What is the Danger Zone?

4-60

Bacterial Spore

A bacterial spore is a structure produced by bacteria that is resistant to many environmental or induced factors that the bacteria may be subjected to. Spores help bacteria survive by being resistant to extreme changes in the bacteria's habitat including extreme temperatures, lack of moisture/drought, or being exposed to chemicals and radiation. Bacterial spores can also survive at low nutrient levels, as well as being resistant to antibiotics and disinfectants. These factors make it nearly impossible to eliminate bacterial spores, as they are found in many places, especially in food products.

What temperature do you need for death of viable cells?

Above 60-80

Are bacterial or fungal endospores heat resistant?

Bacterial

Why are most foodborne pathogens mesophiles?

Because normal body temperature is 37 degrees, which is within their optimum growth range.

Anaerobic storage

Growth of fermentative lactic acid bacteria (Carnobacterium, Leuconostoc) Fermentation of carbohydrates to lactic acid and acetic acid: souring Some strains convert amino acids: occasional sulphide odours

Most pathogens do not grow at what pH?

Less than 4.5

If you keep cold foods at or below 4, growth of most pathogens is inhibited. What pathogens are exceptions?

Listeria monocytogenes Yersinia enterocolitica Clostridium botulinum group 2 **these are psychotrophic pathogens

less than than 10^6 bacteria / g

No noticeable change of food quality

bacteria grow to ~ 10^9 cells / g in food

Properties of food are determined by microbial metabolites (fermented foods)

Extrinsic Factor

Properties of the environment. - Are controlled by the storage environment "where you put the food"

Intrinsic Factor

Properties of the food. - Are controlled by the raw materials or by the product formulation "what you put in the food"

What are the exceptions for pathogen growth below pH 4.5?

Salmonella (4) E. Coli (4) S. aureus (4.2)

Aerobic refrigerated storage

Spoilage by aerobic Pseuodomonas spp. Meat: oxidative breakdown of proteins and lipids; odour and slime after cell count 10^7 is reached

What are the two types of modified atmosphere?

Take away Oxygen (anaerobic): vacuum, N2 inhibits growth of aerobic organisms Add CO2: inhibits growth of aerobic organisms but no lactic acid bacteria

What is the most important factor determining growth of microorganisms in food?

Temperature