4 - Factors that Influence Microbial Growth Flashcards
What factors can be used alone or in combination to limit bacterial growth in a product?
- Temperature
- Redox potential
- pH
- Water activity
What is the most important environmental factor affecting growth and survival of microorganisms?
Temperature
Microbial growth is accomplished by ______________
enzymatic reactions
Thermodynamics tells us that, in a certain range - for every ____C rise in temperature ______________ of an enzyme doubles
10
catalytic rate
Describe a temperature growth curve:
y-axis: growth rate
x-axis: temperature
-minimum: membrane gelling; transport processes so slow that growth cannot occur
-middle: enzymatic reactions occurring at increasingly rapid rates
-optimum temperature: enzymatic reactions occurring at maximal possible rate
-maximum: protein denaturation; collapse of the cytoplasmic membrane; thermal lysis
Psychrotrophs are responsible for growth and food spoilage at ___________________, but grow much faster at room temperatures
refrigeration temperatures
When foods are exposed to temperatures beyond the max or min temperatures of growth cells _____
cells die
Redox potential – measures the ___________________________________________
potential energy difference in a system generated by a coupled reaction in which one substance is oxidized and a second substance is reduced
The electron donor because it reduces the oxidized substance is called the reducing agent (LEO THE LION GOES GER).
reducing agent
_____________ and ___________ of substance are the primary means of generating energy in microbes
Oxidation and reduction
If there is free oxygen it acts as a _______________________, which is a high-energy reaction
terminal electron acceptor
Redox potential in food is influenced by:
- its chemical composition
- processing treatments
- storage condition
Fresh food and plants are in a _______ state because of the reducing potential of biomolecules (____________________-), when cellular respiration stops oxygen diffuses in and changes the redox potential
- reduced
- ascorbic acid, sugars, and –SH protein groups
Aerobes:
need free oxygen O2
Anaerobes:
can only transfer electrons through fermentation, may die in even small amounts of oxygen (they lack superoxide dismutase necessary to scavenge toxic oxygen free radicals)
Facultative anaerobes:
can use free oxygen, bound oxygen (CO2, NO3 or SO4)
Microaerophiles:
grow better in the presence of less oxygen
The most important anaerobe in food is _______________
Clostridium
When oxygen is present, other organisms outcompete ________ or they make organic acids that limit its growth (it can’t grow below pH 4.0)
Clostridium
Clostridium ________ can cause meat putrification
laramie
Clostridium __________ can cause fatal foodborne illness
botulinum
Most bacteria have a pH range of _____ units
2-3
T OR F: Only a few bacteria can grow at pH of less than 2 or greater than 10
true
name the 3 types of bacteria based on their pH range:
- acidophile
- neutrophile
- alkaliphile
In general _____ and _____ can grow at lower pH than bacteria
yests and molds
Gram _ bacteria can grow at lower pH than Gram _
positive
negative
What do we have to look for when choosing an acid to prevent bacterial growth in food?
We have to look at what pH the acid gets dissociated (look at its pKa value)
Name 5 acids commonly used in foods:
- acetic
- propionic
- lactic
- citric
- sorbic
Acids that have a lower ________ rate (weak acids) are more problematic for bacteria
dissociation
Undissociated molecules are __________, they enter into the cell and dissociate to generate ___ in the _________
This causes an increase in cellular internal pH which destroys the proton gradient, and thus the ability of the cells to generate energy
lipophilic
H+
cytoplasm
______ is the solvent of life
water
Water is required to ________, ________, ___________
- solubilize important molecules
- carry away waste
- carry in nutrients
Osmosis definition:
water moves from an area of high water concentration to an area of low water concentration
Cells generally have _______ solutes than the outside environments so water moves into the cells
higher
Nonhalophile bacteria example:
E.coli
Halotolerant bacteria example:
Staph aureus
Halophile bacteria example:
vibrio fischeri
Extreme halophile:
halobacterium salinarum
Osmophiles, organisms are able to live in environments which are high in _______
sugar
Xerophiles, organisms are to live in very ____ environments
dry
What are the 3 methods for removing water from food:
1) Dehydration
2) Crystallization (crystal candies)
3) Adding solutes (salt, sugar, honey, starch) - jellies, honey, salami, jams
Applying 2 or more methods of controlling microbial growth at lower levels can reduce growth, prevent growth or kill microorganisms (what is the concept behind this)?
the hurdle concept
Hurdle technology is more effective when it combines_____________
2 stressors that act by different mechanisms
Hurdle effects can be ______ or _________
additive or synergistic
Claims of synergistic effects must be supported by a ___________ analysis, such as the use of an __________
quantitative
isobologram
Experiments are conducted to determine the _______ of A and B in various _________
MIC
concentrations.
If the points fall on the line the effects are _________
additive
If the points fall below the line the effects are __________
synergistic
If the points fall above the line the effects are _________________
antagonistic
