4 - Factors that Influence Microbial Growth

Question 1

What factors can be used alone or in combination to limit bacterial growth in a product?

Answer 1

• Temperature
• Redox potential
• pH
• Water activity

Question 2

What is the most important environmental factor affecting growth and survival of microorganisms?

Answer 2

Temperature

Question 3

Microbial growth is accomplished by ______________

Answer 3

enzymatic reactions

Question 4

Thermodynamics tells us that, in a certain range - for every ____C rise in temperature ______________ of an enzyme doubles

Answer 4

10

catalytic rate

Question 5

Describe a temperature growth curve:

Answer 5

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

Question 6

Psychrotrophs are responsible for growth and food spoilage at ___________________, but grow much faster at room temperatures

Answer 6

refrigeration temperatures

Question 7

When foods are exposed to temperatures beyond the max or min temperatures of growth cells _____

Answer 7

cells die

Question 8

Redox potential – measures the ___________________________________________

Answer 8

potential energy difference in a system generated by a coupled reaction in which one substance is oxidized and a second substance is reduced

Question 9

The electron donor because it reduces the oxidized substance is called the reducing agent (LEO THE LION GOES GER).

Answer 9

reducing agent

Question 10

_____________ and ___________ of substance are the primary means of generating energy in microbes

Answer 10

Oxidation and reduction

Question 11

If there is free oxygen it acts as a _______________________, which is a high-energy reaction

Answer 11

terminal electron acceptor

Question 12

Redox potential in food is influenced by:

Answer 12

• its chemical composition
• processing treatments
• storage condition

Question 13

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

Answer 13

• reduced

- ascorbic acid, sugars, and –SH protein groups

Question 14

Aerobes:

Answer 14

need free oxygen O2

Question 15

Anaerobes:

Answer 15

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)

Question 16

Facultative anaerobes:

Answer 16

can use free oxygen, bound oxygen (CO2, NO3 or SO4)

Question 17

Microaerophiles:

Answer 17

grow better in the presence of less oxygen

Question 18

The most important anaerobe in food is _______________

Answer 18

Clostridium

Question 19

When oxygen is present, other organisms outcompete ________ or they make organic acids that limit its growth (it can’t grow below pH 4.0)

Answer 19

Clostridium

Question 20

Clostridium ________ can cause meat putrification

Answer 20

laramie

Question 21

Clostridium __________ can cause fatal foodborne illness

Answer 21

botulinum

Question 22

Most bacteria have a pH range of _____ units

Answer 22

2-3

Question 23

T OR F: Only a few bacteria can grow at pH of less than 2 or greater than 10

Answer 23

true

Question 24

name the 3 types of bacteria based on their pH range:

Answer 24

• acidophile
• neutrophile
• alkaliphile

Question 25

In general _____ and _____ can grow at lower pH than bacteria

Answer 25

yests and molds

Question 26

Gram _ bacteria can grow at lower pH than Gram _

Answer 26

positive | negative

Question 27

What do we have to look for when choosing an acid to prevent bacterial growth in food?

Answer 27

We have to look at what pH the acid gets dissociated (look at its pKa value)

Question 28

Name 5 acids commonly used in foods:

Answer 28

- acetic - propionic - lactic - citric - sorbic

Question 29

Acids that have a lower ________ rate (weak acids) are more problematic for bacteria

Answer 29

dissociation

Question 30

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

Answer 30

lipophilic H+ cytoplasm

Question 31

______ is the solvent of life

Answer 31

water

Question 32

Water is required to ________, ________, ___________

Answer 32

- solubilize important molecules - carry away waste - carry in nutrients

Question 33

Osmosis definition:

Answer 33

water moves from an area of high water concentration to an area of low water concentration

Question 34

Cells generally have _______ solutes than the outside environments so water moves into the cells

Answer 34

higher

Question 35

Nonhalophile bacteria example:

Answer 35

E.coli

Question 36

Halotolerant bacteria example:

Answer 36

Staph aureus

Question 37

Halophile bacteria example:

Answer 37

vibrio fischeri

Question 38

Extreme halophile:

Answer 38

halobacterium salinarum

Question 39

Osmophiles, organisms are able to live in environments which are high in _______

Answer 39

sugar

Question 40

Xerophiles, organisms are to live in very ____ environments

Answer 40

dry

Question 41

What are the 3 methods for removing water from food:

Answer 41

1) Dehydration 2) Crystallization (crystal candies) 3) Adding solutes (salt, sugar, honey, starch) - jellies, honey, salami, jams

Question 42

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)?

Answer 42

the hurdle concept

Question 43

Hurdle technology is more effective when it combines_____________

Answer 43

2 stressors that act by different mechanisms

Question 44

Hurdle effects can be ______ or _________

Answer 44

additive or synergistic

Question 45

Claims of synergistic effects must be supported by a ___________ analysis, such as the use of an __________

Answer 45

quantitative | isobologram

Question 46

Experiments are conducted to determine the _______ of A and B in various _________

Answer 46

MIC | concentrations.

Question 47

If the points fall on the line the effects are _________

Answer 47

additive

Question 48

If the points fall below the line the effects are __________

Answer 48

synergistic

Question 49

If the points fall above the line the effects are _________________

Answer 49

antagonistic