Powerpoint 4: Factors that influence microbial growth Flashcards
Which parameters can be used to limit bacterial growth?
- temperature
- pH
- redox potential
- water activity
What is the most important environmental factor affecting the growth and survival of organisms?
Temperature
What does redox potential measure?
measures the potential energy difference in a system generated by a coupled reaction in which one substance is oxidized and a second is reduced
Who is the reducing agent?
The electron donor. It reduces the oxidizing agent.
What are the primary means of generating energy in microbes?
Oxidation and reduction of substances
In what state are fresh fruits and vegetables found?
Reduced state
Microorganisms who can use free oxygen and bound oxygen are called?
Facultative anaerobes
What are microorganisms who can grow better in the presence of less oxygen called?
Microaerophiles
What is a common way to decrease microbial growth?
Modified atmosphere packing
What is the most important anaerobe in food called?
Clostridium
What pH can’t Clostridium grow in anymore?
Below pH 4
What can cause meat putrification
Clostridium laramie
What can cause fatal foodborne illnesses?
Clostridium botulinum
What is controlled atmosphere packaging (CAP)?
The atmosphere in a storage facility is altered and the levels of the gases are continually monitored and adjusted.
- expensive
- long term storage of fruits and vegetables
What is modified atmosphere packaging (MAP)?
- does not require high degree cotrol
- food is enclosed in a high gas barrier packaging material
- air is removed, and flushed with a particular gas or combination of gases
- package is hermetically sealed
Vacuum Packaging (VP)?
- removal of air from the package
- sealing the package hermetically
What is used in the preparation of ready to eat meat?
vaccum packaging VP
Up to how many weeks can VP extend shelf life?
8 weeks
What is used to extend the life of fresh pasta, bakery product, cooked egg products, and fresh seafood?
Gas flushing MAP
What is the pH range of neutrophile bacteria?
6-8
What is the pH range of alkaliphile bacteria?
8-11
What is the pH range of acidophiles?
1-4
In general, what microorganisms grow better at low pH?
-yeast and molds > gram + > gram-
Why are acids with a lower dissociation rate (weak acids) more problematic for bacteria?
- undissociated molecules are lipophilic: they enter into the cell and dissociate to generate H+ in the cytoplasm, causing an increase in the the internal cellular pH
- destroys the proton gradient and ability to generate energy.
What is particularly important in canned food for preservation?
acid
T/F: acids are used in several foods to prevent the growth of pathogens and spoilage bacteria.
true
What is the acid that is used as vinegar, or sodium or calcium salts in >25% in pickles or salad dressings?
Acetic acid
What is acetic acid very effective against?
Bacteria
How does acetic acid’s inhibitory mechanism work?
-neutralizing the electrochemical gradient of the cell membrane as well as denaturing proteins inside the cell walls.
What has been recommended as carcass wash to reduce bacterial loads?
Acetic Acid
What is propionic acid used in?
Used as salts of calcium or sodium in bread, cheese, jam, jellies, and tomato puree.
What are the two microorganisms propionic acid is effective against?
Molds and Bacteria
What is the antimicrobial action of propionic acid?
Acidification of the cytoplasm as well as destabilization of the membrane proton gradients.
Where is lactic acid used?
As acid or as sodium or potassium salts up to 2%.
Where can lactic acid be found?
Carbonated drinks, salad dressing, picked vegetables.
What is lactic acid effective against?
Bacteria
What is citric acid used in?
Used as an acid in >1% drinks, jams, jellies, baking products, cheeses, canned vegetables, and sauces.
T/F: The antibacterial activity of citric acid is unclear.
true
What is sorbic acid used as?
- acid
- salt of sodium, potassium, calcium
- alcoholic and non-alcoholic drinks
- processed fruits and vegetables
- dairy desserts
- confectioneries
- mayonnaise
- salad dressings
- spreads
- mustards
What is sorbic acid most effective against?
Yeast and molds
What is the antibacterial function of sorbic acid?
Inhibits the function of enzymes, the synthesis of the cell wall, protein, RNA, and DNA
What is Benzoic acid used in?
-acid or sodium salt such as alcoholic and non-alcoholic drinks, processed fruits and vegetables, dairy desserts, confectioneries, mayonnaise, salad dressings, spreads, mustard.
How does benzoic acid act?
Inhibits the action of enzymes needed for oxidative phosphorylation
What is the order of the effectivity of natural acids?
From most effective to least effective:
- acetic acid
- propionic acid
- sorbic acid
- benzoic acid
- lactic acid
- citric acid
What does an Aw of 0 indicate?
completely dry
Where can osmophiles grow?
Environments high in sugar
What type of environment can xerophiles grow in?
Very dry
What are the three methods for removing water from food?
1- Dehydration
2-Crystallization
3-Adding solutes (salt, sugar, honey, starch)
When is the hurdle concept most effective?
When it combines two stressors that act by different mechanisms
What technique de-optimizes a variety of factors so that lower concentrations of each needed to inhibit bacterial growth?
Hurdle Concept
What two bacteria can jump over the hurdle of a Pw of 0.97?
Listeria and Salmonella
What bacteria can jump over the hurdle of pH of 5 and Aw of 0.97?
Listeria
salmonella cannot
Why is an isobologram useful?
Can support the quantitative analysis of synergistic effects
What are the effects if the point are on the line?
Additive effects
What are the effects if the points fall below the line?
Synergistic effects
What are the effects if the points are above the line?
Antagonistic effects
