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Food Microbiology > Food Micro - Exam 2 > Flashcards

Food Micro - Exam 2 Flashcards

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1
Q

Bacteria reproduce through what when conditions are favorable?

A

Binary fission

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2
Q

What is a positive outcome of bacteria reproduction?

A

Food fermentations

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3
Q

What is a negative outcome of bacteria reproduction?

A

Spoilage or safety (dec. in food safety)

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4
Q

Microbial growth is the equivalent of what?

A

Population size

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5
Q

Describe the 5 steps of binary fission.

A
  1. Cell replicates its DNA
  2. The cytoplasmic membrane elongates, separating DNA molecules
  3. Cross-wall forms, membrane invaginates
  4. Cross-wall forms completely
  5. Daughter cells form
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6
Q

Microbial growth is measured as growth in what?

A

Numbers (not necessarily size)

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7
Q

Generation time equals what?

A

Doubling time (for microbial generations this is about 7 - 10 minutes)

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8
Q

Generation time (doubling time) depends on what?

A

Conditions (environmental)

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9
Q

Is generation time (double time) the same for each microorganism?

A

No, it is different for each.

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10
Q

Why do we manipulate generation time (doubling time)?

A

To prevent spoilage or safety issues.

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11
Q

What are some optimal conditions for growth of microorganisms?

A

Temperature, salinity, nutrients, etc.

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12
Q

At what temperature do many foodborne pathogens prefer growth around?

A

37ºC

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13
Q

Vibrio parahaemolyticus (usually found in salt water) has a typical generation time of what?

A

10 - 12 minutes

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14
Q

Escherichia coli has a typical generation time of what?

A

15 - 20 minutes

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15
Q

Bacillus cereus has a typical generation time of what?

A

28 minutes

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16
Q

Staphylococcus aureus has a typical generation time of what?

A

27 - 30 minutes

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17
Q

Mycobacterium bovis has a typical generation time of what?

A

960 - 1200 minutes

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18
Q

Bacillus cereus and Staphylococcus aureus usually depend on what for their generation time?

A

Depend on environment

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19
Q

Why do aerobic conditions speed up generation time for Bacillus cereus and Staphylococcus aureus?

A

Because they utilize oxidative phosphorylation.

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20
Q

What three things paved the way for microbiology?

A

Fire, salt, and fermentation.

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21
Q

Early cultures discovered that fire, salt, and fermentation could do what for foods and beverages?

A

Cook, cure, and reduce the pH of foods and beverages

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22
Q

Define intrinsic factors.

A

Characteristics inherent to the food.

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23
Q

What are the major intrinsic factors?

A

Nutrients
pH
Water activity
Antimicrobial
Biological structures
Redox potential

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24
Q

Define extrinsic factors.

A

Characteristics that are external to the foods.

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25
Q

What are the major extrinsic factors?

A

Temperature
Relative humidity
Atmosphere
Byproducts of microbial activity

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26
Q

Growth of microorganisms occurs through what? (2 things)
What does this say about growth rate?

A
  • Proliferation and metabolism
  • Rates differ for microorganisms
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27
Q

Survival of microorganisms means what? (3 things)

A
  • Injured – viable but nonculturable
  • Membrane integrity compromised (leaky cells)
  • Slowed metabolism – focus on repair
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28
Q

What is occurring during the lag phase of a microbial growth curve?

A

Adjusting to surroundings

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29
Q

What is occurring during the logarithmic/exponential phase of a microbial growth curve?

A

High metabolism rates

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30
Q

What is occurring during the stationary phase of a microbial growth curve?

A

Survival and death rates are roughly even within the population.

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31
Q

What is occurring during the death phase of a microbial growth curve?

A

Depletion of nutrients; unsuitable conditions

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32
Q

Which factors are not inherent to food?

A

Extrinsic

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33
Q

Which factors are characteristic of food?

A

Intrinsic

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34
Q

What are the 3 extrinsic factors we need to know for the exam?d

A

Temperature
Atmosphere
Relative humidity

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35
Q

What are the 6 intrinsic factors we need to know for the exam?

A

Nutrients
pH
Water activity
Oxidation/reduction potential
Antimicrobials
Biological structures

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36
Q

Hurdle technologies are what?

A

Additive and synergistic
Hurdle technologies are what we actively do to intervene.

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37
Q

In what foods do we need control of pH and atmosphere? (Hurdle technologies)

A

Fermented foods

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38
Q

In what foods do we need control of aw and pH? (Hurdle technologies)

A

Jams and jellies
- In regard to pH, fruits are naturally acidic.

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39
Q

If we add sugar to fruits to make jams/jellies what will occur?

A

Sugar will bind to H2O and reduce water activity.

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40
Q

In what foods do we need control of pH and temperature? (Hurdle technologies)

A

Range of perishable and shelf-stable foods

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41
Q

In what foods do we need control of temperature and use of bacteriocins/organic acids? (Hurdle technologies)

A

Yogurt and other fermented dairy products

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42
Q

What are psychrophiles?

A

Microorganisms that grow in 0 - 20ºC conditions (they love the cold)

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43
Q

What are psychrotrophs?

A

Microorganisms that grow in 20 - 30ºC conditions (fridge temp).
Capable of less than or equal to 7ºC

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44
Q

What is an example of a psychrotroph?

A

Listeria monocytogenes

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45
Q

What are mesophiles?

A

Microorganisms that grow in 30 - 40ºC conditions.
Capable of 20 - 45ºC.

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46
Q

What is an example of a mesophile?

A

E. Coli and Salmonella

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47
Q

What are thermophiles?

A

Microorganisms that grow in 55 - 65ºC conditions.
Capable of greater than or equal to 45ºC.

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48
Q

Most microorganisms grow in what temperature zones?

A

Psychrotrophic and mesophilic temperature zones.

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49
Q

What is the temperature danger zone?

A

40 - 140ºF (5 - 60ºC)

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50
Q

Cooling rates impact what?

A

Microorganism growth rate

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51
Q

Cooling rates vary by what?

A

Food types and amount

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52
Q

Cooling rates impact microorganism growth rate by impacting what?

A

Membrane fluidity

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53
Q

Can cooling rates alter virulence?

A

Yes, there is reduced expression of virulence genes at reduced temperatures and enhanced expression of virulence at optimal growth temperatures.

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54
Q

What microorganisms serves as an example of cooling rates altering virulence?

A

Listeria monocytogenes

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55
Q

Microorganisms require what specific conditions for growth?

A

Atmospheric conditions

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56
Q

What are some obligate aerobes?

A

Pseudomonas
Molds
Bacillus Cereus

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57
Q

What are some facultative anaerobes?

A

Listeria monocytogenes
Salmonella
E. Coli

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58
Q

What are some obligate anaerobes?

A

Clostridium spp.

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59
Q

What are some aerotolerant anaerobes?

A

Lactobacilli

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60
Q

What are some microaerophiles?

A

Campylobacter jejuni

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61
Q

We can manipulate O2, N2, and CO2 content to what?

A

Restrict growth
Inactivate microorganisms

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62
Q

What are 3 examples of controlling the extrinsic factor atmosphere?

A

Vacuum-packaging
Modified atmosphere packaging
Controlled atmosphere storage

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63
Q

What does vacuum packaging help with?

A

It slows spoilage and controls oxidation

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64
Q

What does modified atmosphere packaging help with?

A

It increases CO2 levels (by 7 - 10%) and decreases O2 levels (to less than 1%).

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65
Q

What is an example of a food that we use modified atmosphere packaging in order to control its atmosphere?

A

Lettuce

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66
Q

What does controlled atmosphere storage help with?

A

It allows for control O2 levels (3%) and controlled CO2 levels (3%).

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67
Q

What is an example of a food that we use controlled atmosphere storage in order to control its environment?

A

Apples

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68
Q

What are some nutrients that affect microorganism growth?

A

Water and energy sources (such as carbon, sugar, nitrogen, and phosphorus)
- energy sources affect enzymatic activity
- these include macro and micronutrients

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69
Q

Are nutrients in some foods more accessible than others?

A

Yes

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70
Q

What is one way nutrient availability is impacted?

A

By processing (slicing, macerating, inclusions)

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71
Q

What is another way nutrient availability is impacted?

A

By competition (starter cultures will out-compete pathogens in fermented foods)

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72
Q

pH is a measurement of what and is measured on a scale of what?

A

A measurement of acidity
0 - 14
pH = -log [H+]

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73
Q

Moth pathogens require what pH range for growth?

A

pH greater than or equal to 4.4 - 4.6
(however, some spoilage microorganisms can grow in acidic foods)

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74
Q

What is an example of a spoilage microorganism that can grow in acid foods?

A

Lactic acid bacteria (LAB)

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75
Q

Foodborne microorganisms prefer what pH range?

A

6 - 7 pH

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76
Q

What microorganism can grow as low as 4.4 pH?

A

Clostridium botulinum

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77
Q

What are the 5 major effects of pH on microorganisms?

A
  1. undissociated acid crosses membrane
  2. acid dissociates within cytoplasm
  3. anion can disrupt cellular function
  4. more cellular energy spent to maintain intracellular balance (F-ATPase system and passive diffusion of H+)
  5. Dissociated acid cannot cross membrane when charged
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78
Q

Low-acid foods are commonly associated with what?

A

Outbreaks

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79
Q

Low-acid foods means what?

A

pH on the higher end (around neutral)

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80
Q

Adding acid to lower pH will result in what?

A

Acidified foods
- ex: cucumbers pickled with acetic acid

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81
Q

Acid foods have a naturally low pH of what?

A

Less than 4.6 pH

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82
Q

Define antimicrobials.

A

Substances natural to the foods with inhibitory or inactivating properties.

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83
Q

What are some examples of antimicrobials?

A

Bacteriocins
Organic acids and iso-a-acids (hops)
Essential oils –> thyme oil, eugenol, allicin
Enzymes –> lysozyme

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84
Q

How does a lysozyme exert antimicrobial activity?

A

It is found in the peptidoglycan in the cell wall and disrupts the cell (hydrolyzes beta linkages).
It is effective against gram-positive bacteria.

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85
Q

The Lactoperoxidase system exerts what intrinsic activity?

A

Antimicrobial activity

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86
Q

What is the lactoperoxidase system?

A

A naturally occurring inhibitory system in milk

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87
Q

What does the lactoperoxidase system consist of?

A

Lactoperoxidase
Thiocyanate
Hydrogen peroxide (in natural amounts)
- However, there is typically additional thiocyanate and hydrogen peroxide added

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88
Q

What is the lactoperoxidase system inhibitory to?

A

Effective against gram-positive and negative microorganisms

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89
Q

What can the lactoperoxidase system do to the shelf life of milk?

A

Can extend shelf life from 2 - 5 days

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90
Q

The lactoperoxidase system works synergistically (cooperatively – both benefit) with what two enzymes?

A

Lactoferrin and lysozyme

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91
Q

Oxidation / Reduction potential (Eh) is the measure of what?

A

The measure of tendency to gain or lose electrons

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92
Q

What does it mean for something to be reduced?

A

To have negative electric potential.
To favor anaerobic growth.

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93
Q

What does it mean for something to be oxidized?

A

To have positive electric potential.
To favor aerobic growth.

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94
Q

Eh changes within a food based on what 3 things?

A

Microorganism growth (resulting in respiration)
Processes that impact the atmosphere (M
Cooking / heating (forces oxygen out)

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95
Q

Anaerobes need what type of environment?

A

Reduced environment

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96
Q

Aerobes need what type of environment?

A

Oxidized environment

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97
Q

Define water activity.

A

The ratio of free, available water within a food.

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98
Q

What does available water mean?

A

Available for use by microorganisms

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99
Q

An aw (water activity) of 0.0 means what?

A

Bone dry

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100
Q

An aw (water activity) of 1.0 means what?

A

Pure water

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101
Q

Water activity greatly impacts what 3 things?

A

Physical characteristics of food
Chemical reactions
Microbial growth

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102
Q

Most bacteria have what type of water activity?

A

Fairly high water activity (0.91 - 0.88 at 25ºC)

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103
Q

What can grow at lower water activites?

A

Mold (but needs a little higher water activity in order to produce toxin)

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104
Q

How does lower water activity affect shelf life?

A

It allows for longer shelf life

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105
Q

How does higher water activity affect shelf life?

A

It causes shorter shelf life

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106
Q

What is the mechanism behind water activity?

A

Movement of water molecules from high to low aw.
This is known as osmotic stress.

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107
Q

What is the measurement of water activity and how do you measure it?

A

Ratio of free, available water within a food
Equilibrate liquid-phase water in sample to vapor-phase water in headspace
(Relative humidity is measured to indirectly determine water activity)

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108
Q

What are some consequences of osmotic stress that can challenge the food industry?

A

Dormancy
Filaments (elongation without separation until more favorable conditions)
Cross-protection (same protein used to respond to multiple stresses)

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109
Q

What is the typical aw (water activity) of fresh, raw fruits, vegetables, meat, and fish?

A

Greater than 0.98 (this is a high water activity)
- Usually high water activity constitutes greater than 0.95

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110
Q

What is the typical aw (water activity) of cooked meat and bread?

A

0.95 - 0.98

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111
Q

What is the typical aw (water activity) of cured meat products and cheeses?

A

0.91 - 0.95

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112
Q

What is the typical aw (water activity) of sausages and syrups?

A

0.87 - 0.91

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113
Q

What is spoilage?

A

Physical, chemical, enzymatic or biologcial changes

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114
Q

Spoilage can be the result of biological changes caused by what?

A

Bacteria, yeasts, or molds

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115
Q

What can prevent spoilage?

A

Extrinsic / intrinsic factors can be manipulated to extend the shelf life
Addition of preservatives
Prevention of exposure to spoilage microorganisms

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116
Q

Antimicrobials do what?

A

Inhibit microbial growth with bacteriostatic action

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117
Q

Bacteriostatic action does what?

A

Prevents multiplication

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118
Q

Antimicrobials also act as?

A

Biological preservation

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119
Q

What are some examples of antimicrobials?

A

NaCl
Acids
Nitrites
Phosphates
Sulfites
Lysozyme/lactoferrin/lactoperoxidase system

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120
Q

What is an example of antimicrobial inhibition?

A

Organic acids to treat produce

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121
Q

How do acids exert antimicrobial activity?

A

Manipulation of pH

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122
Q

Do weak acids have more effective antimicrobial activity and why or why not?

A

Yes, because they are able to dissociate within the cytoplasmic membrane.

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123
Q

What are preservatives?

A

A food additive that may:
- reduce or prevent browning
- reduce or prevent oxidation (antioxidant)
- stabilize the food formulation
- serve as an antimicrobial agent

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124
Q

Are preservatives bacteriostatic (prevents multiplicaiton)?

A

Yes

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125
Q

Traditional preservatives and antimicrobials can be?

A

Naturally derived or synthetically made

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126
Q

Do all preservatives have to be approved for use?

A

Yes

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127
Q

Natural antimicrobials or preservatives are:

A

From natural sources
Organic
Generally fit the clean label

128
Q

What is clean labeling?

A

Based on the idea that consumers are intimidated by technical language

129
Q

Give an example of clean labeling.

A

Saying “celery powder” instead of “nitrites”

130
Q

How can you determine if there is spoilage?

A

Changes in sensory attributes that make the food unacceptable to the consumer

131
Q

What are the 5 changes in sensory indicating spoilage?

A

Taste: sour, bitter, putrid
Texture: mushy, slimy
Smell: FAs, esters, aldehydes
Appearance: discoloration, structural
Sound: think “chips or popcorn”

132
Q

Determine spoilage: <10^6 bacteria

A

Microbial spoilage generally not recognized

133
Q

Determine spoilage: 10^6 - 10^7 bacteria

A

Some foods show early stages of changes

134
Q

Determine spoilage: 10^7 - 10^8 bacteria

A

Spoilage associated with most foods
Off colors associated with meats and vegetables

135
Q

Determine spoilage: 10^9 bacteria

A

Almost all foods display obvious indications of spoilage

136
Q

Determine spoilage: >10^9 bacteria

A

Obvious structural changes

137
Q

Lower water activity and lower pH usually mean what?

A

Longer shelf life –> less spoilage

138
Q

What is the origin of spoilage microorganisms in red meat?

A

Hide / hair
Hooves
Mouth
Intestines

139
Q

What are the typical spoilage microorganisms in red meat?

A

Staphylococcus
Micrococcus
Pseudomonas
Lactic acid bacteria (LAB)
Yeasts
(all of these microorganisms can tolerate or require oxygen)

140
Q

What does it mean for meat to be comminuted?

A

Ground / combined

141
Q

How does spoilage occur in comminuted meat?

A

Contamination during processing
Distribution of contaminants
Increased surface area = increased nutrient availability
Mixture of environment (aerobic and anaerobic)

142
Q

A higher microbial load means what in regard to shelf life?

A

A shorter shelf life

143
Q

What is the origin of spoilage microorganisms in poultry?

A

Skin
Feathers
Feet
Intestines
Litter
Transportation

144
Q

What are the typical spoilage microorganisms in poultry?

A

Clostridium estertheticum (formerly Laramie) –> causes sulfide odor –> terrible for spoilage because forms spores
Pseudomonas
Lactic acid bacteria (LAB)

145
Q

What is the origin of spoilage microorganisms in seafood?

A

Environment
Storage facility
Workers

146
Q

What is the typical spoilage microorganism in seafood?

A

Pseudomonas (a psychrotroph) –> able to process the high protein / low carb content –> important for fish

147
Q

Do spoilage microorganisms in seafood vary by water?

A

Yes

148
Q

What are the typical cool water spoilage microorganisms?

A

Psychrotrophs (specifically pseudomonas)

149
Q

What are the typical warm water spoilage microorganisms?

A

Mesophiles (specifically bacillus and micrococcus)

150
Q

Active spoilage in produce is due to what?

A

Plant pathogens

151
Q

Passive spoilage in produce is due to what?

A

Opportunistic pathogens (wound - induced)

152
Q

What are some primary components of spoilage microorganisms in produce?

A

Cellulose
Pectin
Cutin
(degradative enzymes produced to break down components)

153
Q

What are some examples of degradative enzymes produced to break down components in produce?

A

Pectinases produced by Botrytis cinerea
Penicillium spp
Erwinia carotovora

154
Q

Is post-harvest mold due to wounds in produce?

A

No, it can occur with or without wounds

155
Q

Erwinia carotovora is a spoilage microorganism in produce that causes what?

A

Soft rot
Damaged tissues allow invasion by Erwinia
- to prevent this you need to scrub potatoes
- passive spoilage because through damaged tissue (through wound)

156
Q

What organization prevents spoilage in produce?

A

Good Agricultural Practices (GAPs)

157
Q

What does GAPs do to prevent spoilage in produce?

A

Control of land, water, and air
Post-harvest processes –> washing (acts as control, not necessarily an intervention)
Temperature
Atomosphere

158
Q

What does GAPs do to prevent spoilage in produce?

A

Control of land, water, and air
Post-harvest processes –> washing (acts as control, not necessarily an intervention)
Temperature
Atmosphere

159
Q

Is the spoilage rate different for organic produce?

A

No, same for organic and non-organic produce
Fresh produce = no GMOs (people think it lasts longer but this is not true)

160
Q

Grain is a dry, desiccated product, which means what about its water activity?

A

It has a low water activity (aw < 0.65)

161
Q

What happens when condensation is present in grain?

A

Molds gain foothold –> mycotoxin production
- specifically Aspergillus mold

162
Q

How can we prevent spoilage in grains?

A

Milling and grinding reduces microbial load
Control of storage conditions
Extrusion

163
Q

What are signs of spoilage in breads and pastries?

A

Presence of yeast and mold

164
Q

How can we prevent spoilage in bread and pastries?

A

Preservatives
Storage conditions (controlled humidity)

165
Q

What is the typical shelf life of milk?

A

10 - 15 days if heated properly to eliminate most vegetative bacteria (pathogens)
Higher protein milk and soy milk = longer shelf life because lactose free

166
Q

Spoilage after shelf life in milk occurs because of what?

A

Psychrotrophs

167
Q

Specifically what spoilage microorganisms/mechanisms typically spoil milk after shelf life?

A

Lactic acid bacteria (heterofermentative) –> acetic acid
Proteolytic metabolism –> roping and clotting

168
Q

How must raw milk be preserved?

A

Must be chilled to 7ºC within 2 hours after milking, never to exceed 10ºC

169
Q

Why is raw milk very susceptible to spoilage?

A

Because it contains several microorganisms, and when it comes out, it is already in the temperature danger zone
Raw milk = never safe –> should be pasteurized

170
Q

What is the oldest known antimicrobial preservative?

A

Sodium chloride (NaCl)

171
Q

Sodium chloride is known to cause what?

A

Plasmolysis –> cell shrinkage due to presence in a hypertonic solution (more solutes in external solution than inside cell)

172
Q

Sodium chloride can combine with other hurdles such as:

A

desiccation, heat, etc.

173
Q

Sodium chloride inhibits foodborne pathogens at what percentage and water activity?

A

13% and aw = 0.90

174
Q

How does sodium chloride prevent food spoilage?

A

Generally bacteriostatic (prevents multiplication of bacteria) by prompting plasmolysis
L. monocytogenes can survive in salt solution (NaCl causes plasmolysis)
Staphylococcus aureus can grow at aw 0.83 if other conditions are right (NaCl has aw = 0.90)

175
Q

List the antimicrobial organic acids from most preventative to least.

A

Acetic > propionic > lactic > citric
- efficacy impacted by lipophilic nature

176
Q

How do organic acids prevent spoilage?

A

Cross cell membrane into cytoplasm (molecule must be protonated and uncharged)

177
Q

What happens when the pH of food is higher than pKa of organic acid?

A

The molecules dissociate and organic acid cannot cross membrane

178
Q

Benzoates are antimicrobials that are commonly used as what and function best at what pH?

A

Commonly used as sodium or potassium benzoate
Functions best at lower pH (< 4.0)

179
Q

How do benzoates prevent spoilage?

A

Forms benzoic acid, which enters cell like other acids

180
Q

Benzoic acid is present in what foods?

A

Apples
Blackberries
Cranberries
Tomatoes
Cultured dairy products
Cinnamon

181
Q

What is the first chemical preservative approved by FDA?

A

Benzoic acid

182
Q

What are 3 common parabens?

A

Methyl
Propyl
Heptyl
Parabens = alkyl esters of para-hydroxybenzoic acid

183
Q

How do parabens (antimicrobials) prevent spoilage?

A

Act on membrane, reduces fluidity
Leads to DNA damage and prevention of replication

184
Q

What is the effective range pH for parabens?

A

pH 3 - 8
Remains in the undissociated form up to pH 8.5

185
Q

Parabens are most effective against what?

A

Molds and yeasts (antifungal)
Attacks membrane and causes leakage

186
Q

What are parabens used for?

A

Baked goods
Beverages
Fruit products
Syrups
Salad dressings
Fermented foods

187
Q

Nitrites (antimicrobials) are present in what?

A

Leafy greens and root vegetables

188
Q

Nitrites are used as a what for meats?

A

Curing ingredient for meat (bacon, hot dogs, and ham)
Adds pink color and flavor profile

189
Q

Nitrites are effective at what pH and oxygen requirement?

A

Effective at low pH and anaerobic environment

190
Q

Nitrites are paired with ascorbate to inhibit what microorganisms? How do they inhibit?

A

C. botulinum and L. monocytogenes
Interfering with cell wall synthesis, breaking apart nucleotides, derivatives (enzymes and proteins) can disrupt metabolism

191
Q

Sorbates (an antimicrobial) are commonly used as what?

A

Potassium sorbate

192
Q

Sorbates are effective at what pH?

A

pH < 6.5

193
Q

Sorbates are antifungal and antibacterial but not against what? And how?

A

Fermenters
Disrupts membrane, induces oxidative stress (DNA damage)

194
Q

Sorbates are used in what products to prevent spoilage?

A

Fermented products
Fruit products
Carbonated and fruit beverages

195
Q

How do sulfites (antimicrobials) prevent spoilage?

A

Targets cytoplasmic membrane, DNA replication, protein synthesis and enzymes

196
Q

Why are sulfites used in wines?

A

To allow for malolactic fermentation without inhibiting fermentation of yeasts
Also used in vegetable and fruit products
Antioxidant to prevent browning

197
Q

The effectiveness of sulfites is dependent on what? When are they active?

A

pH and form
Active when undissociated

198
Q

Lysozymes (antimicrobials) are present where?

A

Milk
Eggs
Tears

199
Q

How do lysozymes prevent spoilage?

A

They are heat stable
They target cell wall by breaking down peptidoglycan
Effective against gram (-) and (+), but more effective against gram (+)

200
Q

Lactoferrin (an antimicrobial) is present where?

A

Milk

201
Q

How does lactoferrin prevent spoilage?

A

Binds iron and limits growth of pathogens that require high iron levels
(i.e. Clostridium, E. Coli, listeria, Pseudomonas, salmonella)

202
Q

Lactoperoxidase system (antimicrobial) is naturally present where?

A

Milk
Can be enhance with increasing concentrations of components

203
Q

How does the lactoperoxidase system prevent spoilage?

A

Works synergistically with lysozyme, lactoferrin, and hydrogen peroxide

204
Q

What is the main concept regarding oxidative phosphorylation?

A

Oxygen serves as terminal electron acceptor and yields energy.

205
Q

What is the main concept regarding fermentation and what byproducts does it yield?

A

No oxygen in fermentation, so sugar will receive electron and is partially oxidized.
- yields some energy and incompletely oxidized byproducts (lactic acid, acetic acid, ethanol, etc.)

206
Q

Fermentation is an anaerobic process that produces a number of what byproducts?

A

Acetic acid
Lactic acid
Alcohol
Gas (CO2)

207
Q

Fermented foods provide advantages for what 3 things?

A

Preservation: longer shelf life by preventing spoilage
Safety: byproducts influence intrinsic factors
Nutrition: nutrient availability, beneficial byproducts

208
Q

What are the key players in fermentation?

A

Lactic acid bacteria
Yeasts
(They will need to be tolerant of oxygen until fermentation where they will then be deoxygenated)

209
Q

When did fermentation of cheese begin?

A

> 7,000 years ago in Mediterranean

210
Q

When did fermentation of beverages begin?

A

7,000 years ago in Babylon

211
Q

When did fermentation of breads begin?

A

> 5,000 years ago in Egypt

212
Q

When did fermentation of vegetables begin?

A

3,500 years ago in China

213
Q

What is the primary byproduct for alcoholic fermentation with yeasts? Give an example of this process.

A

Alcohol can be main or secondary byproduct
- ex: bread leavening by yeasts
- ex: ethanol evaporates during baking

214
Q

Fermentation of lactic acid occurs in what products?

A

Dairy products
Bread
Fermented vegetables

215
Q

Lactic acid fermentation does what to acidity?

A

Lactic acid increases acidity (increased acid, decreased pH)

216
Q

What flavor profile does lactic acid fermentation create?

A

Sour flavor profile

217
Q

Different pathways in lactic acid fermentation produce what?

A

Lactate (each lead to a variety of end products)

218
Q

What is a major fermenter in fermentation process of lactic acid?

A

Lactic acid bacteria

219
Q

There is a large group of fermenters in fermentation of lactic acid, what are they?

A

Lactobacillus
Leuconostoc
Pediococcus
Lactococcus

220
Q

What is/are the byproducts of homofermentative (homolactic) fermentation?

A

Primary byproduct is lactic acid

221
Q

What is/are the byproducts of heterofermentative (heterolactic) fermentation?

A

Multiple byproducts

222
Q

Homolactic fermentation mostly produces lactic acid with the help of what fermenters?

A

Lactococcus
Pediococcus
Streptococcus
Some lactobacillus

223
Q

Give an example of homolactic fermentation.

A

Fermented meats and vegetables

224
Q

Heterolactic fermentation produces multiple byproducts with the help of what fermenters?

A

Lactobacillus
leuconostoc

225
Q

What are some of the multiple byproducts of heterolactic fermentation?

A

Acetic acid
Propionic acid
Carbon dioxide
Acetaldehyde

226
Q

Heterolactic fermentation allows for what?

A

Flexible use of sugars
More flavor profiles
(is able to multitask)

227
Q

Give an example of heterolactic fermentation.

A

Vegetables
Yogurt
Sourdough bread

228
Q

Natural/native starter cultures are derived from where?

A

The environment
Considered “wild”

229
Q

Fermentation of starter cultures causes what to occur between batches? Give an example.

A

Variablility
- ex: sourdough bred at farmers market

230
Q

What is back-slopping in starter culture fermentation?

A

Using a part of a finished product to start the new
Some consistency
- ex: sourdough

231
Q

Designed or lab-grown starter cultures are present where?

A

In proprietary blends

232
Q

Designed or lab-grown starter cultures are genetically enhanced for what?

A

Flavor compounds or performance

233
Q

Designed or lab-grown starter cultures have what consistency?

A

Highest consistency

234
Q

What does the clarification step in the dairy fermentation process do?

A

Removes sediment (leukocytes that may contain Listeria monocytogenes)

235
Q

The formulation step in dairy fermentation depends on what?

A

The end-product

236
Q

Pasteurization removes what from diary?

A

Unwanted bacteria

237
Q

What does the homogenization step of dairy fermentation do?

A

Prevents ingredient separation during fermentation

238
Q

What are some key fermenters in milk fermentation in yogurt?

A

Streptococcus thermophilus
Lactobacillus bulgaricus
Acidophilus
Bifidobacterium spp.

239
Q

What does milk fermentation in yogurt do to lactose (milk sugar)?

A

Decreases lactose content and forms lactic acid

240
Q

What does the lactic acid do to the milk (in yogurt)?

A
  • Lowers pH (drops to about 4.8 when done; safe to consume, but less than or equal to 4.6 is no longer safe)
  • Causes protein denaturation
241
Q

What happens to casein during milk fermentation in yogurt?

A

It is broken down and reassembles (coagulation)

242
Q

What are the key byproducts in milk fermentation in yogurt?

A

Acetaldehyde
Aromas
Bacteriocins
Acid

243
Q

What are the 7 factors affecting microbial growth during cheese fermentation?

A
  • starter cultures and byproducts
  • pH and organic acids
  • Redox potential
  • Nutrients (sugars, proteins)
  • Water activity (water and salt concentration)
  • Temperature
  • Bacteriocins
244
Q

What decreases throughout the cheese fermentation process?

A

Microbial diversity

245
Q

Starter cultures in cheese are capable of what?

A

Metabolizing lactose and casein

246
Q

What are common in cheese fermentation?

A

Homolactics

247
Q

What provide flavor in cheese fermentation?

A

Heterolactics (specifically diacetyl, CO2)

248
Q

What are the 4 major steps in cheese fermentation?

A
  1. Milk
  2. Cultures
  3. Rennet (protease enzyme)
  4. Salt
249
Q

How does coagulation during cheese fermentation?

A

Microbes and enzymes hydrolyze casein

250
Q

Cutting curd during cheese fermentation does what?

A

Increases microbial activity by increasing surface area

251
Q

Cooking during the cheese fermentation process does what?

A

Selects for specific enzymatic and microbial activity

252
Q

Salting during the cheese fermentation process does what?

A

Reduces moisture and brines

253
Q

Aging of cheese is what type of process?

A

Controlled process (controlled through temperature and humidity)

254
Q

What are some examples of inedible cheese rinds?

A

Wax
Paper
Bark

255
Q

What are some examples of edible cheese rinds?

A

Bloomy (snowy white, ripened by mold –> ex: Brie, Camembert)
Washed (reddish-orange, from bacteria Brevibacterium linens)
Natural (hard layer –> ex: cheddary, parmesan)

256
Q

Molds can also be used for what in cheese fermentation?

A

Veining (poke holes where oxygen can promote growth of mold)
- ex: Penicillium roqueforti

257
Q

Where does the microbiome of raw milk come from?

A

Teats
Handlers
Environment
Equipment

258
Q

Raw milk is exposed to what specific pathogens?

A

Brucella abortus
Campylobacter spp.
E. Coli
Salmonella
Listeria monocytogenes
Staphylococcus aureus

259
Q

Raw milk is responsible for many outbreaks such as what?

A

Typhoid fever
Salmonellosis
Campylobacteriosis
Brucellosis

260
Q

Cheeses made from raw milk are regulated through what process?

A

Aging process

261
Q

What is the standard aging requirement according to 21 Code of Federal Regulations (CFR) section 133?

A

Requires 60 days aging at > 35ºF (this is based on earlier data from > 60 years ago)

262
Q

What two microorganims can survive for longer periods of time when it comes to cheese aging?

A

Salmonella
E. coli

263
Q

Native microorganisms on surface of produce (vegetables) offer what?

A

Diversity

264
Q

Lactic acid bacteria in vegetable fermentation is tolerant to what?

A

Salt and anaerobic environment
(Metabolism and byproducts make them good competitors)

265
Q

What is the final pH after vegetable fermentation?

A

Usually below 4.6

266
Q

Give an example of vegetable fermentation.

A

Cabbage
Cucumbers
Olives

267
Q

What are the 5 steps of vegetable fermentation?

A
  1. Start with healthy vegetables
  2. Pretreat if necessary (washing, blanching, cooking)
    a. additional processing such as slicing, cutting, or
    maceration
  3. Place into fermentation vessel
    a. additional optional ingredients (salt, starter cultures)
  4. Submerge and cover vegetables with brine
  5. Allow fermentation to take place, checking at points to determine product readiness
268
Q

What are the main fermenters in fermentation of Sauerkraut (cabbage)?

A

Microbial succession of:
Leuconostoc mesenteroides
Lactobacillus plantarum
Lactobacillus brevis

269
Q

What is the final pH after cabbage fermentation?

A

3.8 - 4.1

270
Q

What are the main fermenters in pickle (cucumber) fermentation?

A

Lactobacillus plantarum (homofermentative)
Heterofermentative LAB (may cause floaters)

271
Q

Pickle (cucumber fermentation) occurs via?

A

Natural fermentation

272
Q

What is the final pH of pickle (cucumber) fermentation?

A

3.7

273
Q

What does the color of olives indicate?

A

Green = unripe
Black = ripe

274
Q

What are the main fermenters in olive fermentation?

A

Pediococcus spp.
Leuconostoc mesenteroides
Lactobacillus plantarum
Brevis

275
Q

How must unripened olives be treated? And how long is fermentation?

A

Must be treated in 2% NaOH to remove oleuropein (antibacterial compound)
Long fermentation ( > 1 month)

276
Q

How must ripened olives be treated? And how long is fermentation?

A

May not require NaOH solution (depends on targeted flavors)
shorter fermentation ( > 2 weeks)

277
Q

Olives are washed and placed where for fermentation?

A

In brine (5 - 10 % NaCl)

278
Q

What are the steps for fermentation of meats?

A
  1. Grinding raw meat
  2. Blended with ingredients (salt, nitrites, spices)
  3. Package
  4. Incubate for fermentation
  5. Final heating step
  6. Dry Package
279
Q

What are the starter cultures present during meat fermentation and what conditions can they grow in?

A

Pediococcus acidilactici
Can grow at higher temperatures (43 - 50 ºC)
Can grow at high salt concentration (about 6%)
Added sugars can promote growth

280
Q

If fermented sausages are shelf-stable they must include what ingredients that inhibit growth of microorganisms?

A

Nitrites / curing agents
Acid (pH < 5.0)
Specific moisture to protein ratio (3.1 : 1.0)

281
Q

Cocoa beans contain what type of coating?

A

Mucilaginous coating with sugars

282
Q

What does this mucilaginous coating on cocoa beans mean for fermentation?

A

Beans with mucilage are fermented in piles by native microbes (2 - 8 days)

283
Q

Where are cocoa bean pods located?

A

theobroma cacao in tropic regions (South America and Western Africa)

284
Q

A careful drying process is required to end cocoa bean fermentation with what?

A

The right flavor profile and moisture content

285
Q

What are the 6 steps of chocolate processing in cocoa bean fermentation?

A
  1. Roasting (preservation and flavor)
    a. Rapid (high heat, strong flavors)
    b. Slow (low heat, subtle flavors, floral notes)
  2. Milling (grinding into chocolate liquor (no alcohol)
  3. Pressing (separate cocoa powder from butter)
  4. Conching (kneading / smoothing of liquor, releases flavors)
  5. Tempering (controlled heating process to develop cocoa butter crystals that result in smooth, shiny surface)
  6. Molding (pouring liquid chocolate into molds for shaping)
286
Q

What are the main fermenters in coffee bean fermentation?

A

Coffea arabica
C. canephora
C. robusta

287
Q

Coffee bean fermentation with native LAB will remove what?

A

The mucilaginous layer
(Last thin layer of cellulose and remaining microbes are washed away with water)

288
Q

Extended fermentation of coffee beans may allow for what?

A

Yeast and molds to compete with LAB and spoil product

289
Q

What are the coffee processing steps?

A
  1. Drying (following fermentation to drop moisture to 11%)
  2. Roasting (develop flavor profile)
  3. Grinding and brewing
290
Q

What is Kopi Luwak?

A

Fermentation of beans within digestive tract of Asian palm civet

291
Q

What is the basis of yeast fermentation?

A

Processes carbohydrates / starchy grains to leaven and produce flavor

292
Q

What is the most common grain?

A

Wheat flour
Gluten formed from glutenin and gliadin; developed during kneading, provides structure and elasticity

293
Q

What is the most common yeast for bread fermentation?

A

Saccharomyces cerevisiae

294
Q

What is the main byproduct of Saccharomyces cerevisiae during bread fermentation?

A

Carbon dioxide (about 40% expansion)

295
Q

Yeast fermentation produces what two byproducts?

A

Ethanol (vaporized during baking)
CO2 (yields bubbles and gives structure)

296
Q

What does proofing during bread fermentation consist of?

A

Temperature (27ºC)
Humidity
Time

297
Q

Sourdough bread uses a mixture of what?

A

Yeast and LAB

298
Q

The acidic and tangy flavor profile in sourdough is due to what?

A

The byproducts

299
Q

San Francisco sourdough consists of what specific yeast and bacteria mixture?

A

Yeast: Candida milleri
Bacteria: Lactobacillus Sanfrancisco
(blend used continuously for > 140 eyars)

300
Q

What byproducts will pyruvate yield in beverage fermentation?

A

CO2
Ethanol
Some acids

301
Q

Wine and beer have a variety of what fermenters?

A

Varieties of yeasts

302
Q

Kombucha is fermented with what?

A

SCOBY (symbiotic culture of bacteria and yeasts)

303
Q

What are the benefits of beverage fermentation?

A

Preservation
Nutrients
Safety
Recreation

304
Q

Fermentation is mainly affecting what intrinsic factor?

A

Nutrients

305
Q

What are the 5 steps in beer production?

A
  1. Malting (part affecting nutrients)
  2. Mashing
  3. Wort boiling
  4. Fermentation
  5. Postfermentation processing
306
Q

Beer uses the same yeast as bread but is looking for what byproduct instead?

A

Alcohol

307
Q

What are hops and what do they do during beer fermentation?

A

Hops = flower cones of hop plant
Provide aroma, bitterness, antimicrobial effects for alpha - acids

308
Q

Yeast used in beer fermentaion depend on what?

A

Style of fermentation and temperature

309
Q

What type of yeast is used for top yeast fermentation (warmer brew)?

A

Saccharomyces Cerevisia

310
Q

What type of yeast is used for bottom yeast fermentation (colder brew)?

A

Saccharomyces uvarum
(S. eubayana and S. pastorianus are also good for colder temperatures)

311
Q

Secondary fermentation is additional fermentation that will require more what?

A

Nutrients and microbes

312
Q

What are the two types of beet fermentation?

A

Top fermentation (warmer brewing temps)
Bottom fermentation (colder brewing temps)

313
Q

What are the antimicrobials present in beer?

A

Ethanol
CO2
Hops

314
Q

Spoilage in beer is due to?

A

Wild and aerobic yeasts

315
Q

What are some safety methods used during beer fermentation to prevent from spoilage?

A

Pasteurization
Cold pasteurization
Antimicrobial hurdles

316
Q

If we see Saccharomyces before adding actual yeast during beer fermentation what does this indicate?

A

This indicates that we have a problem
(should not be added until after adding yeast)

Food Microbiology (1 decks)

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