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NUT2003 > Microbes in Food > Flashcards

Microbes in Food Flashcards

1
Q

Requirement of Microbes

A

Appropriate environment

Appropriate Nutrition

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2
Q

How do bacteria reproduce

A 
Binary Fission
1 cell gives 2 
gives 4
gives 8
Exponential
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3
Q

Generation time

A

Time it takes between each division

Clostridium perfringens is 7.4 minutes

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4
Q

How to plot bacteria growth

A 
Log paper to give straight line
LogNt = 0.201n + LogN0
Nt - number of cells over a period of time
No - starting number
n- number of generations
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5
Q

Phases of bacteria growth in batch

A

lag
log
Stationary
Death

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6
Q

Lag phase

A

Cells grow and adapt to new environement

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7
Q

Log phase

A

Cells multiply rapidly and exponentially

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8
Q

Stationary phase

A

No net increase in cell
Death = growth
Because resources at capacity

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9
Q

death phase

A

Death of cells more frequent and larger than cell growth

Lack of nutrients

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10
Q

Bacteria

A

Prokaryote

Binary fission

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11
Q

Yeast

A

Eukaryote
Unicellular
Multiply by buddying

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12
Q

Moulds

A

Eukaryote
Multicellular
Asexually reproduce

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13
Q

Food production use of microbes

A 
Dairy
Fermented beverages
Sauerkraut
Sausages
Sourdough
Soy sauce
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14
Q

Non-microbial food spoilage

A

Physical (dehydration)
Chemical (oxidation of FA)
Infestation (insects and rodents)

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15
Q

Microbial food spoilage

A

Direct effect on growth
Effect microbial enzymes on food
Has to gain access to food with correct conditions
Detect presents at 10^6-10^8

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16
Q

Growth rate of microbes

A

Bacteria > Yeast > Moulds

17
Q

Temperature and microbe growth

A

Same starting temperature but a lower log number of cells per gram then take longer to spoil

If lower the temperature to fridge temp (4 degrees) takes longer to spoil even if at same starting log number.

18
Q

Conditions to consider microbial growth

A

pH
Aw (water activity)
Nutrient
Atmosphere

19
Q

Mesophiles

A

Minimum temp - 5-15 degrees
Optimal - 30-40 degrees
Max temp - 40-47

20
Q

Psychrophiles

A

Minimum temperature - -5-5 degrees
Optimal - 12-15
Max - 15-20

21
Q

Psychrotrophs

A

Min - -5-5
Optimal - 25-30
Max - 30-35

22
Q

Thermophiles

A

Optimal above 45

23
Q

What effect microbial population

A

Hygiene
Contamination
Processing
Preservation

24
Q

Why microbial testing

A

Safety to consumers
Stability of shelf life
Level of sanitation used during handling
Whether they meet acceptable standards

25
Q

Quantitative microbial testing

A

Provide and estimate of microbial load

Aerobic plate count or standard plate count

26
Q

Qualitative microbial test

A

Detect presence of specific foodborne pathogens using selective agar

27
Q

Antigen-antigen microbial tests

A

ELISA testing

28
Q

Nucleic acid base pair recognition

A

Probe featuring NA from target organism applied to NA extract from food samples
PCR

29
Q

Food preservation principles

A

Minimise food spoilage or food poisoning organisms

Reduce micro-organisms to start with, inhibit growth or kill microorganisms

30
Q

High temperature

A

Kills microbes
Thermal Pasteurisation
Thermal Sterilisation

31
Q

Low Temperature

A

Inhibition of growth
Chilled storage
Freezing

32
Q

D value

A

Time for number of microorganisms to decrease by one decimal place

High D value means greater heat resistance

33
Q

Z value

A

Number of degrees to increase D value 10 folds

34
Q

Sterilisation

A

Inactive micro-organisms and enzymes
Deliver sensory and nutritional properties
Time influenced by - heat resistance and pH

Low acid food - anaerobic spores forming pathogens - need to remove clostridium botulinum spores
12D
121 degrees for 2.52 minute

In high acid food generally less severe

35
Q

Pasteurisation

A

Mild treatment below 100 degrees
Kills pathogens, enzyme activity and spoilage enzymes

Low acid food - eliminate pathogenic bacteria
Liquid egg - salmonella 64.4 degree for 2.5mins
Milk - mycobacterium tuberculosis

High acidic food - inactivate enzymes as pathogens cant grow

NUT2003 (20 decks)

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