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Food Microbiology > Spoilage > Flashcards

Spoilage Flashcards

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1
Q
  1. What are the six causes of spoilage?
A

Microbial
Mechanical
Insect damage
Chemical and enzymatic
Physical
Physiology of the product

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2
Q

What is the difference between a spoiled product and actual spoilage?

A

Spoiled product: quality perceived unacceptable
Spoilage: process of decreasing quality

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3
Q

What does the shelf life depend on (microbiologically)?

A

Initial contamination of the food and growth rate of microorganisms

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4
Q

What are some examples of primary contamination? (give two)

A

Animals/plants (raw materials)

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5
Q

What are some examples of secondary contamination? (give three)

A

Water
Equipment
Air
People
Vermin

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6
Q

What are the four phases of microbial growth?

A

Lag phase
Exponential phase
Stationary phase
Death phase

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7
Q

What are the two main shapes of bacteria?

A

Cocci and rods

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8
Q

What is the average size of yeasts & molds?

A

10 micrometers

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9
Q

What mechanism do yeasts use to grow?

A

Budding

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10
Q

Do viruses grow on food?

A

No

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11
Q

Are viruses important in the appearance of foodborne illnesses? Why?

A

Yes because they can produce mycotoxins

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12
Q

Give an example of a parasite

A

Ticks

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13
Q

What are the environmental factors that influence the viability of a microorganism?

A

Suitable ecological niche and competitive advantage

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14
Q

In which phase of the growth curve are bacteria adapted to the environment?

A

Exponential phase

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15
Q

What is growth kinetics?

A

Study of increase of cell numbers in time

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16
Q

What are 2 ways to increase the shelf life of a product in terms of growth kinetics?

A

Reducing the initial contamination or increasing the generation time

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17
Q

What is the difference between intrinsic and extrinsic factors

A

Intrinsic factors are properties of the food itself and extrinsic is properties of the environment the food is in

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18
Q

How are m.o in food classified? (e.g. photo lithotroph)

A

Mostly chemo heterotrophs

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19
Q

What is an example of a physical nutrient barrier?

A

Shell of nuts, peels

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20
Q

What is the aim of antimicrobial barriers?

A

Hinder growth through lack of access to water and nutrients, leave microorganisms without environment protection

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21
Q

What do the following four enzymes degrade?: Pectolytic, amylytic, lipolytic, proteolytic

A

Pectolytic: pectin
Amylytic: Starch
Lipolytic: lipids
Proteolytic: proteins

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22
Q

How does preservation work?

A

By changing product formulation (increasing/decreasing nutrients) or processing (introducing/removing barriers)

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23
Q

What are the pH optimums for foodborne bacteria, yeast and mold?

A

Bacteria: around 7
Yeast: around 4.5
Mold: around 3.5

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24
Q

Which kind of acids (dissociated or undissociated) can easily pass through membranes? How do they do this?

A

Undissociated acids through proton motive force

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25
Q

How is pH applied in preservation?

A

Fermentation: Lactic acid bacteria lowers pH and inhibits growth of pathogens
Acid preservatives

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26
Q

How do yeasts and molds make the environment more suitable for pathogens?

A

They dissimilate the acid and alter the pH

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27
Q

How do aerobic organisms get oxygen?

A

Oxidative phosphorylation with oxygen as electron acceptor

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28
Q

What is a facultative anaerobe?

A

Does not require oxygen but grows better with oxygen

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29
Q

What are ways to change the redox potential of a product?

A

Milling/grinding and lowering to increase Eh microbial growth lowers Eh

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30
Q

What m.o are more sensitive to CO2?

A

Molds, oxidative gram negative bacteria

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31
Q

What m.o are more resistant to CO2?

A

Gram positive bacteria and yeasts

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32
Q

What is water activity?

A

Measure of free water in food

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33
Q

What is the aw min of xerophilic and osmophilic m.o?

A

Xerophilic: 0.6
Osmophilic: 0.62

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34
Q

What are 3 ways to lower the aw of the product?

A

Adding solutes
Removing water
Combined application

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35
Q

What are 3 natural preservatives in milk?

A

Lysozyme
Lactoferrin
Antibodies

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36
Q

What are 3 natural preservatives in eggs?

A

Lysozyme
Avidine
Conalbumine

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37
Q

What m.o are inhibited by the addition of acids?

A

Lactic acid inhibits gram negatives and listeria
Yeasts, molds and lactic acid bacteria by the rest

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38
Q

What do SO2 and nitrate do to help preserve a product?

A

Disrupt microbial metabolism

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39
Q

What is important to keep in mind when using freezing to preserve a product?

A

Physchrophiles and psychrotolerant m.o can still grow, freezing stops growth but allows survival

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40
Q

When does the growth rate stop increasing?

A

When the optimal temperature is reached

41
Q

What are implicit factors?

A

Properties of m.o themselves and interactions between them

42
Q

What is the most important implicit property that influences spoilage?

A

Specific growth rate during optimal conditions

43
Q

Which are killed more easily? Cells in exponential/stationary phase?

A

Exponential phase

44
Q

What environmental stresses can affect the physiological state of a microorganism?

A

Injury due to freezing or dissecation

45
Q

What are the 5 most important interactions between microorganisms?

A

Competition
Obligate symbiosis
Mutualism
Commensalism
Antagonism

46
Q

What is the difference between symbiosis, commensalism and mutualism?

A

Symbiosis is obligate (both microorganisms need it), mutualism both benefit from each other, commensalism is only one benefits from the other one

47
Q

What is amensalism?

A

One microorgannism generates harmful compounds for another one

48
Q

What is the Hurdle effect?

A

Combination of sub optimal factors that preserves the product sufficiently

49
Q

What are the 4 options to evaluate spoilage or health risks?

A

Ask an expert
Challenge test
Storage test
Predictive microbiology

50
Q

What are the pros and cons of asking an expert?

A

Pros: quick, proposal told if good or bad idea
Cons: Not quantitative

51
Q

What are the pros and cons of a challenge test?

A

Pro: representative for the product and organism
Con: Time consuming, expensive, only representative of the conditions set

52
Q

What are primary growth models?

A

Describe contamination levels in time described by the specific growth rate

53
Q

What are secondary growth models?

A

Describe the influence of intrinsic and extrinsic factors of the food on the growth rate

54
Q

What is gamma modeling?

A

Combination of primary and secondary modeling

55
Q

What three factors do food manufacturers have to balance out?

A

Food quality, shelf life and costs

56
Q

What three effects does processing want to have on microorganisms?

A

Keep microorganisms out
Kill microorganisms
Keep microorganisms from growing

57
Q

What main 4 methods are used to kill microorganisms?

A

Radiation
High pressure
Pulsed electric fields
Heat inactivation

58
Q

Which of the radiation rays are more effective in killing microorganisms and why?

A

Gamma rays because they have deep penetration

59
Q

What are the advantages and disadvantages of using high pressures to kill microorganisms?

A

Pros: instant and uniform, low effect on the quality
Cons: some enzymes are difficult to inactivate, difficult to scale up

60
Q

What survives after pasteurization?

A

Some pathogens and sporeformers

61
Q

What survives after appertization?

A

(sterilization): non pathogenic survivors that can’t develop in the product

62
Q

What is blanching used for?

A

Decontamination and enzyme inactivation

63
Q

What does the Sous vide environment consist of?

A

Vacuum product with heat treatment and refrigeration

64
Q

What is the unit of D value?

A

Time

65
Q

True or false: D value goes up as the temperature goes up

A

False d value goes down

66
Q

What is a D value?

A

Time required to reduce cell number by 1 log

67
Q

What factors influence the increase the D value? (name two)

A

pH, aW, temperature, food matrix

68
Q

What is the Z value?

A

Change in temperature that yields a 1 log change in the D value

69
Q

What is the unit of Z value?

A

Temperature

70
Q

What is the Z value of vegetative cells?

A

5 degrees

71
Q

What is the Z value of spores?

A

10 degrees

72
Q

What is bigger? D/Z value of spores or vegetative cells?

A

D and Z value of spores is bigger than in vegetative cells

73
Q

What is the F value?

A

Integrated lethal effect

74
Q

What is the Lethal rate?

A

Relative inactivation rate at a certain temperature

75
Q

What are the 3 main sources of contamination of raw milk?

A

Dirt on exterior of teats
Interior of teats
Milking equipment

76
Q

What are the 4 ways of contamination of teats?

A

Feed, feces, bedding and soil

77
Q

Which microorganisms naturally occur in soil that can contaminate cows?

A

Spores (bacillus) and Listeria monocytogenes

78
Q

Which microorganisms naturally occur in feces that can contaminate cows?

A

Campylobacter, Salmonella, E. coli

79
Q

What is mastitis?

A

Inflammatory disease in mammary tissue

80
Q

What are preventive measures for milk contamination?

A

Don’t feed moldy silage
Clean teats and equipment
Milk quality payment system

81
Q

What are the main curative measures for milk spoilage?

A

Kill microorganisms with heat (Pasteurization and sterilization)
Remove microorganisms (Bactofugation and microfiltration)
Prevent microorganisms from growing with low temperature, Aw and pH

82
Q

Which microorganisms survive pasteurization?

A

Bacillus cereus
Lactobacillus
Microbacterium

83
Q

Which microorganisms survive UHT?

A

Bacillus and other sporeformers

84
Q

Which microorganisms can grow post pasteurization?

A

Pseudomonas, alcaligenes, Acinetobacter, psychrobacter

85
Q

Why do microorganisms still grow in milk even if its chilled?

A

Because milk is still a good medium for growth (good nutrients)

86
Q

What is spoilage association determined by?

A

Raw material flora
Processing
Storage conditions
Preservation

87
Q

What happens to the pH of the meat after the animal dies? Why?

A

It drops from neutral to 5.5 because lactic acid is produced due to gycolysis

88
Q

Where in the animal can you find spoilage associated microflora? Where can you find safety associated microflora?

A

Spoilage: hide, skin, hair and feathers
Safety: gastro intestinal tract

89
Q

Where in the animal is relatively free of microorganisms?

A

Internal organs and muscles

90
Q

About how many microorganisms does a primal cut of meat have?

A

10^2-10^4

91
Q

In what temperature is meat normally stored at? Which flora can grow? Name two examples

A

Low temperatures, psycho-tolerant flora such as Pseudomonas, Enterobacteriaceae and Lactic Acid Bacteria can grown

92
Q

What 4 preservative factors can be used to conserve meat?

A

Exclude oxygen
Increase CO2
Freezing
Heat treatment

93
Q

What are the advantages and disadvantages of MAP?

A

Maintains red color of meat
Spoilage flora depends on temperature of storage

94
Q

What are the advantages and disadvantages of freezing?

A

No microbial growth under -18C
Growth after defrosting, enzymes of killed microorganisms can still act

95
Q

What heat treatments can be used on meat?

A

Pasteurization and sterilization

96
Q

What 2 components help preserve cured meat?

A

Salt and nitrite

97
Q

What issues can arise with cutting of deli meat?

A

Souring and discoloration in package
Contamination with psychrotolerant bacteria

98
Q

Why does fish have such a short shelf life?

A

Because the death struggle consumes all sugars and there is no post mortem acidification

99
Q

Why do cut vegetables have a shorter shelf life than their uncut counterparts? Name 4 factors that influence this.

A

Nutrients available
Aw is higher
More oxygen interacting
Contamination spreads

Food Microbiology (4 decks)

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