Create an account
What are intrinsic factors?
*Factors inherent to the food
- Available Water
- Oxidation-Reduction Potential
- Antimicrobial Constituents
- Biological Structures
(2) Water Activity
- partial pressure of water above the material / partial pressure of pure water at the same temperature
- equal to the equilibrium relative humidity (ERH), expressed as a fraction
- the higher the water activity, the more likely there will be microbial growth
- the lower the water activity, the less likely there will be microbial growth
- by lowering the water activity, we are increasing the length of the lag phase of growth and decreasing the final population
(3) Oxidation-Reduction Potential (Eh)
- substrate is OXIDIZED when it GAINS an electron
- substrate is REDUCED when it LOSES an electron
- substance that gives up electrons is the reducing agent
- substance that takes up electrons is the oxidizing agent
- when electrons are transferred from one compound to another, potential difference is created
- what affects this? poising capacity, oxygen tension, access to the atmosphere
What are the main types of microorganism?
(4) Facultative Anaerobes
Oxygen-loving microbes; can't live without O2; high positive Eh needed
- Bacillus, mold, yeast
Requires oxygen to survive, but requires environments containing lower levels of oxygen
- Lactobacilli, Campylobacter
Able to grow in presence/absence of O2; Capable of producing energy through aerobic respiration and then switching back to anaerobic respiration
- E. coli
(4) Nutrient Content
In odrer to grow and function, microbes require:
- Energy Source (AA, sugars, alcohols)
- Nitrogen Source (AA)
- Vitamins/Growth Factors
(5) Antimicrobial Constituents
Examples of these include:
- Plants have essential oils (cloves, allicin in garlic, eugenol in cinnamon, thymol in oregano)
- Cow's milk contains lactoferrin and lactoperoxidase
- Eggs contain lysozyme
(6) Biological Structures
Some foods provide protection against the entry of microbes, such as:
- Shell of nuts
- Ring of melons
- Hide of animals
- Shell of eggs
- Skin of fish and meats
What are extrinsic factors?
- Relative Humidity
- Presence/Conc. of Gases
- Presence/Conc. of Other Microbes
(1) Temperature - What are the types of microbes?
Are capable of growth and reproduction in cold temperatures (Min, Optimum, Max?)
Psychrophiles (0, 15, 25)
Rre capable of surviving or even thriving in a cold environment but have a optimum near a value of the mesophiles (Min, Optimum, Max?)
Psychrotrophs (0, 25, 40)
Grows best in moderate temperature, neither too hot nor too cold (Min, Optimum, Max?)
Mesophiles (10, 35, 45)
(2) Relative Humidity
- Affects the aw within food and growth of microorganism at surfaces
- When low aw valued foods are placed in a high humidity environment, the food picks up moisture until equilibrium (vice versa)
- The higher the T, the lower the RH
(3) Presence/Conc. of Gases
- CO2 and O2 most important with control of microbes; used with atmospheric packaging
- O3 ozone has been used for antimircobial activity
(4) Presence/Conc. of Other Microbes
Some organisms can produce substances that inhibit/are lethal to other microbes; these include:
- Hydrogen Peroxide
- Organic Acids
Please allow access to your computer’s microphone to use Voice Recording.
Having trouble? Click here for help.
We can’t access your microphone!
Click the icon above to update your browser permissions and try again
Reload the page to try again!Reload
Press Cmd-0 to reset your zoom
Press Ctrl-0 to reset your zoom
It looks like your browser might be zoomed in or out. Your browser needs to be zoomed to a normal size to record audio.
Please upgrade Flash or install Chrome
to use Voice Recording.
For more help, see our troubleshooting page.
Your microphone is muted
For help fixing this issue, see this FAQ.
Star this term
You can study starred terms together