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NU FS 363 - food microbiology > Intrinsic and Extrinsic microbial growth factors > Flashcards

Intrinsic and Extrinsic microbial growth factors Flashcards

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1
Q

what are the 3 extrinsic factors?

A

Temperature, [gases] and relative humidity
- controlled by storage environment ; where you put the food

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2
Q

what are the 5 intrinsic factors?

A

1) pH
2) Moisture content
3) Oxidation
4) Content of nutrients / antimicrobial constituents
5) physical structure / barrier
- what you put in the food (controlled by raw material or product formulation)

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3
Q

what is the difference between an intrinsic factor and extrinsic?

A

Intrinsic factors are controlled by what you put in the food and extrinsic factors are controlled by where you put the food

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4
Q

what is the danger zone?

A

4-60 degrees celcius

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5
Q

what are the three parameters of temperature in controlling bacterial growth?

A

T min -minimum T of growth
T opt - optimum T of growth
T max - max T of growth

-specific for the conditions and bacterial species

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6
Q

what is the optimum T for psychrophiles?

A

< 20 degrees C
-Love cold; adapted to cold environments but not common in foods

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7
Q

what is the optimum T for psychrotrophs? what are examples?

A

optimum @ 20 degrees C but grow starting at 5
- tolerate cold; adapted to ambient temperature in environment

Listeria monocytogenes, pseudomonas spp.

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8
Q

what is the optimum T for Mesophiles? what are examples?

A

30-40 degrees C
-love ambient; adapted to vertebrate animals (E.coli and Staphylococcus)

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9
Q

what is the min growth T for mesophiles?

A

7 degrees C
-no growth at refrigerator T

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10
Q

what is the max growth T for mesophiles?

A

40-60 degrees

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11
Q

what is the optimum T for thermophiles? what are examples? where is this a concern?

A

> 45 degrees C
-Love warm; Geobacillus stearothermophilus
-spoilage in tropical climates

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12
Q

what is the optimum T for hyperthermophiles?

A

> 80 degrees C
-they love very warm

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13
Q

at what T does destruction of most bacterial endospores occur?

A

> 100 - 121 degrees C

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14
Q

what T are vegetative cells killed?

A

60 - 80 degrees C

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15
Q

what is the max number of bacteria cells possible on a surface?

A

10 ^12
- 12D concept

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16
Q

what occurs when there is 10^6 / g bacteria on a food?

A

there is no noticeable change in food quality

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17
Q

what occurs when there is 10 ^ 9 cells / g in a food?

A

bacteria begin to grow and the food properties are determined by microbial metabolites

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18
Q

True or False: bacterial endospores are heat resistant?

A

true
-they are kill > 121 degrees

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19
Q

Explain the survival rate of fungal spores based on T?

A

most are as heat sensitive as vegetative cells
-killed at 60 - 80 degrees C

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20
Q

does anaerobic storage cause off odours in meat?

A

no, it causes souring

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21
Q

does aerobic storage cause souring of meat?

A

no it causes off odours and putrefaction

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22
Q

what is broken down in aerobic spoilage of meat? what bacteria cell count is needed to reach this?

A

oxidative breakdown of proteins and lipids
-odour and slime after cell count of 10^7

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23
Q

what is broken down in anaerobic spoilage of meat?

A

fermentation of carbs to lactic acid occurs
-organic acids lead to souring
- souring and slime formation

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24
Q

how does relative humidity affect bacterial growth?

A

water is needed for microbial growth
-increased humidity will allow for growth (high Rh)

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25
Q

what occurs with a high Rh and refridgeration?

A

condensation

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26
Q

what makes blue steak safe to eat?

A

the physical barrier of the inside the meat to contaminants allows for the muscle of the meat to be sterile

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27
Q

what determines a microorganisms ability to utilize different energy sources?

A

the type of enzymes it produces

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28
Q

what kind of enzymes are needed for starch utilization?

A

amylolytic enzymes

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29
Q

what kind of enzymes are needed for protein utilization?

A

protease

30
Q

what kind of enzymes are needed for lactose utilization?

A

beta- galactosidase

31
Q

what does it mean for an organism to be fastidious?

A

they require sugars, amino acids and vitamins to utilize energy (lactic acid bacteria)

32
Q
A
33
Q

what defence system do egg whites and saliva have in common?

A

they contain lysosomes to hydrolyse cell walls

33
Q

what systematic defense system is common in garlic, onions and mustard?

A

they have glucosinolates that generate isothiocyanates to oxidise thiol groups in proteins

33
Q

what system defense in common in milk?

A

lactoperoxidase system that react with thiol groups to reduce oxidative stress

34
Q

what pH resists most pathogen growth?

A

< 4.5

34
Q

what are the exceptions to the pathogens that grow <4.5 pH

A

Salmonella and E.coli = 4.0
S. aureus = 4.2

35
Q

at what pH do bacterial endospores not germinate at?

A

< 4.5

36
Q

what are the exceptions to the bacterial endospores that grow at a pH < 4.5?

A

Alicyclobacillus acidoterrestris
- contributes to spoilage of fruit juices

37
Q

what microorganisms commonly grow at a pH < 4.5?

A

lactic acid bacteria, yeasts and mould

38
Q

what is considered a high acid food? and lolw acid?

A

< 4.5 = high acid
> 4.5 = low acid

39
Q

how do we treat high acid vs low acid spores?

A

high acid - pasteurize

low acid - pasteurize and refrigerate or sterilize to kill spores

40
Q

are the effects of organic acids (lactate and acetate) or pH stronger?

A

the inhibitory effects of organic acids are stronger

41
Q

at what pH do mold/yeast grow?

A

pH 1.5 - 3.5

42
Q

at what pH does Acetobacter spp. grow?

A

pH 2.4

43
Q

at what pH do many Lactobacillus spp. grow?

A

pH 3.5

44
Q

at what pH does E. coli, Salmonella and S. aureus grow?

A

pH 4.0 - 4.2

45
Q

at what pH does C. botulinum grow?

A

pH 4.5 - 5.0

46
Q

at what pH does Vibrio parahaemolyticus grow?

A

pH 4.8

47
Q

how does ripening affect pH?

A

it can increase pH by 0.5 units upon ripening

48
Q

what effect does microbial metabolism have on acidic and fermented foods?

A

causes alkalinization

49
Q

what is the range of Aw that most foods fall into?

A

0.7 - 1.0

50
Q

what 2 things can you add to reduce water activity? why?

A

10% sucralose
10% NaCl

-sugar and salt are both hygroscopic so the addition of them allows water to bind to these molecules and reduce the free water available for microbial growth

51
Q

at what Aw is crispness lost?

A

> 0.5

52
Q

at what Aw is there rapid lipid oxidation?

A

0 - 0.2

53
Q

at what Aw do browning rxns occur?

A

0.2 - 0.6

54
Q

at what Aw does mold growth begin?

A

0.6

55
Q

at what Aw does yeast growth begin?

A

0.8

56
Q

at what Aw does spoilage bacteria growth begin?

A

0.9
- however, most are inhibited below 0.93

57
Q

at aW of 0.92 or less what occurs?

A

inhibition of growth pathogens and toxin produced by S. aureus

58
Q

what are halophiles or halotolerant bacteria? at what aW do they grow?

A

salt loving or salt tolerating bacteria
- they grow at an aW > 0.75
-found in soy sauce

59
Q

what are osmotolerant yeasts? at what aW do they grow?

A

yeast that tolerates a high [inorganic compounds]
-grow at aW > 0.61

60
Q

what are Xerophilic molds?
at what aW do they grow?

A

molds that tolerate dry conditions
-grow with aW > 0.61

61
Q

what 3 methods can decrease aW?

A

1) drying
2) dry salting
3) brine solution

62
Q

how long should food being sold be able to go without going bad?

A

3 weeks
1 week- distribution
1 week -shelf life
1 week -in consumer house

63
Q

what foods are common in an oxidizing environment? why?

A

fruit, veg, fat, wine, beer, meat and any processed foods w added fat
- oxidizing environments are created when O2 is available to oxidize the food and cause a loss of electrons

64
Q

what foods are common in a reducing environment? why?

A

fermented foods, canned/ vacuum sealed, foods high in antioxidants and foods stored in modified atmospheres
- reducing atmospheres do not have O2 available which causes a gain in electrons and aids in preservation

65
Q

what microorganism is able to grow in environments with high redox potential?

A

Clostridia

66
Q

what are the guidelines for cooling cooked meat?

A

to avoid the danger zone (4 - 60 degrees C) meat should be cooled down to 4 degrees C within four hours of cooking period
- should be cooled to 21 degrees C within 2 hours to prevent multiplication of bacteria

67
Q

what is the hurdle concept for bacterial growth?

A

Instead of relying on one preservation method a combination of methods is applied. Each hurdle weakens or stresses bacteria, yeast, or molds, and the combined effect creates an environment where microbial growth is significantly limited

NU FS 363 - food microbiology (6 decks)

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