Powerpoint 4: Factors that influence microbial growth

Question 1

Which parameters can be used to limit bacterial growth?

Answer 1

• temperature
• pH
• redox potential
• water activity

Question 2

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

Answer 2

Temperature

Question 3

What does redox potential measure?

Answer 3

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

Question 4

Who is the reducing agent?

Answer 4

The electron donor. It reduces the oxidizing agent.

Question 5

What are the primary means of generating energy in microbes?

Answer 5

Oxidation and reduction of substances

Question 6

In what state are fresh fruits and vegetables found?

Answer 6

Reduced state

Question 7

Microorganisms who can use free oxygen and bound oxygen are called?

Answer 7

Facultative anaerobes

Question 8

What are microorganisms who can grow better in the presence of less oxygen called?

Answer 8

Microaerophiles

Question 9

What is a common way to decrease microbial growth?

Answer 9

Modified atmosphere packing

Question 10

What is the most important anaerobe in food called?

Answer 10

Clostridium

Question 11

What pH can’t Clostridium grow in anymore?

Answer 11

Below pH 4

Question 12

What can cause meat putrification

Answer 12

Clostridium laramie

Question 13

What can cause fatal foodborne illnesses?

Answer 13

Clostridium botulinum

Question 14

What is controlled atmosphere packaging (CAP)?

Answer 14

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

Question 15

What is modified atmosphere packaging (MAP)?

Answer 15

• 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

Question 16

Vacuum Packaging (VP)?

Answer 16

• removal of air from the package

- sealing the package hermetically

Question 17

What is used in the preparation of ready to eat meat?

Answer 17

vaccum packaging VP

Question 18

Up to how many weeks can VP extend shelf life?

Answer 18

8 weeks

Question 19

What is used to extend the life of fresh pasta, bakery product, cooked egg products, and fresh seafood?

Answer 19

Gas flushing MAP

Question 20

What is the pH range of neutrophile bacteria?

Answer 20

6-8

Question 21

What is the pH range of alkaliphile bacteria?

Answer 21

8-11

Question 22

What is the pH range of acidophiles?

Answer 22

1-4

Question 23

In general, what microorganisms grow better at low pH?

Answer 23

-yeast and molds > gram + > gram-

Question 24

Why are acids with a lower dissociation rate (weak acids) more problematic for bacteria?

Answer 24

• 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.

Question 25

What is particularly important in canned food for preservation?

Answer 25

acid

Question 26

T/F: acids are used in several foods to prevent the growth of pathogens and spoilage bacteria.

Answer 26

true

Question 27

What is the acid that is used as vinegar, or sodium or calcium salts in >25% in pickles or salad dressings?

Answer 27

Acetic acid

Question 28

What is acetic acid very effective against?

Answer 28

Bacteria

Question 29

How does acetic acid's inhibitory mechanism work?

Answer 29

-neutralizing the electrochemical gradient of the cell membrane as well as denaturing proteins inside the cell walls.

Question 30

What has been recommended as carcass wash to reduce bacterial loads?

Answer 30

Acetic Acid

Question 31

What is propionic acid used in?

Answer 31

Used as salts of calcium or sodium in bread, cheese, jam, jellies, and tomato puree.

Question 32

What are the two microorganisms propionic acid is effective against?

Answer 32

Molds and Bacteria

Question 33

What is the antimicrobial action of propionic acid?

Answer 33

Acidification of the cytoplasm as well as destabilization of the membrane proton gradients.

Question 34

Where is lactic acid used?

Answer 34

As acid or as sodium or potassium salts up to 2%.

Question 35

Where can lactic acid be found?

Answer 35

Carbonated drinks, salad dressing, picked vegetables.

Question 36

What is lactic acid effective against?

Answer 36

Bacteria

Question 37

What is citric acid used in?

Answer 37

Used as an acid in >1% drinks, jams, jellies, baking products, cheeses, canned vegetables, and sauces.

Question 38

T/F: The antibacterial activity of citric acid is unclear.

Answer 38

true

Question 39

What is sorbic acid used as?

Answer 39

- acid - salt of sodium, potassium, calcium - alcoholic and non-alcoholic drinks - processed fruits and vegetables - dairy desserts - confectioneries - mayonnaise - salad dressings - spreads - mustards

Question 40

What is sorbic acid most effective against?

Answer 40

Yeast and molds

Question 41

What is the antibacterial function of sorbic acid?

Answer 41

Inhibits the function of enzymes, the synthesis of the cell wall, protein, RNA, and DNA

Question 42

What is Benzoic acid used in?

Answer 42

-acid or sodium salt such as alcoholic and non-alcoholic drinks, processed fruits and vegetables, dairy desserts, confectioneries, mayonnaise, salad dressings, spreads, mustard.

Question 43

How does benzoic acid act?

Answer 43

Inhibits the action of enzymes needed for oxidative phosphorylation

Question 44

What is the order of the effectivity of natural acids?

Answer 44

From most effective to least effective: - acetic acid - propionic acid - sorbic acid - benzoic acid - lactic acid - citric acid

Question 45

What does an Aw of 0 indicate?

Answer 45

completely dry

Question 46

Where can osmophiles grow?

Answer 46

Environments high in sugar

Question 47

What type of environment can xerophiles grow in?

Answer 47

Very dry

Question 48

What are the three methods for removing water from food?

Answer 48

1- Dehydration 2-Crystallization 3-Adding solutes (salt, sugar, honey, starch)

Question 49

When is the hurdle concept most effective?

Answer 49

When it combines two stressors that act by different mechanisms

Question 50

What technique de-optimizes a variety of factors so that lower concentrations of each needed to inhibit bacterial growth?

Answer 50

Hurdle Concept

Question 51

What two bacteria can jump over the hurdle of a Pw of 0.97?

Answer 51

Listeria and Salmonella

Question 52

What bacteria can jump over the hurdle of pH of 5 and Aw of 0.97?

Answer 52

Listeria | salmonella cannot

Question 53

Why is an isobologram useful?

Answer 53

Can support the quantitative analysis of synergistic effects

Question 54

What are the effects if the point are on the line?

Answer 54

Additive effects

Question 55

What are the effects if the points fall below the line?

Answer 55

Synergistic effects

Question 56

What are the effects if the points are above the line?

Answer 56

Antagonistic effects