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Food Microbiology > Thermal Death > Flashcards

Thermal Death Flashcards

1
Q

What is the difference between pasteurization and sterilization?

A

Pasteurization only reduces #

Sterilization KILLS ALL.

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2
Q

What are some ways to extend shelf life?

A
  • Reduce the increase of microorganisms
  • Use pH, preservatives, drying, radiation.
    Use of:
    1. Bacteriostatic stops active growth
    2. Bactericidical kills microbes
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3
Q

What are examples of bacteriostatic?

A

Freezing, osmotic pressure, desiccation and pH

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4
Q

What are some examples of bactericidal?

A

Heating, radiation, chemical. Sterilization

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5
Q

Bactericidal is meant for?

A

Spores and cells. Kill by baking, boil, frying or microwave. Exceeds 100C

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6
Q

What is the purpose of cooking? (at what temp)

A

< or = 100C to enhance flavor

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7
Q

What is the purpose of blanching?

A

<100C removes oxygen, destroys enzymes (not cooking b/c not held long enough at the temp, still kills enzymes)

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8
Q

Drying/ concentration

A

<100C Removes water, extends storage life.

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9
Q

Pasteurization

A

60-80C Kills target pathogens and spoilage microorganisms. Kills all vegatative cells, but spores are still pressent.

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10
Q

Sterilzation

A

> 100C Kills all microorganisms, including spores. (Use pressure to go over 100C).

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11
Q

What are the benefits of heath processing?

A

Cheap, quick, easy, may improve flavor (cooking), may inactivate undesirable enzymes ( blanching), enhances storage life of a product (drying), inactivation of pathogens and spoilage organisms (pasteurization).

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12
Q

Heat treatments: A few things about it.

A

Organisms specific sensitivity ( in a given environment
Rate of killing is log
Function of temp an time
For a time and temp there’s a constant % destroyed.

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13
Q

When performing heath processing caculations it’s good to know a few things like…

A

Concentration of microorganisms,
acceptable concentration of microorganisms that can survive
Thermal resistance of target organisms (most heat tolerant, establish temp requirements)
TIME AND TEMP relationship required for destruction.

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14
Q

1 log cycle is?

A

The time and temperature it takes to decrease the population by 90%. (from log 6 to log 5)

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15
Q

Thermal death is a ………….cycle.

A

log linear cycle
- given a specific time interval and temperature, the same % of population will be destroyed, regardless of population present.

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16
Q

What does a log cycle tell you if you have the time required to destroy one log cycle (90%), and you know the desired thermal reduction (# log cycles) it tells you…

A

The time it will take for you to get to the # of logs required.

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17
Q

If # of microorganisms increase, heating time will also have to increase..why?

A

To bring the time down to an acceptable level.

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18
Q

D value!!!!

DOES NOT MEAN SLOPE OR RATE

A

Expressed as time ( decimal reduction time)

Time to decrease Microbial population by 1 log (90%) at a given temp in a given system.

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19
Q

Explain when D would change?

A

Depends on species,Aw, composition of food (fat stabilized it), and temperature used. It tells u the sensitivity of an organism to heat treatment.

20
Q

D90= time

A

D90 means at 90C and the smaller the D value, the quicker the orgnaisms will die

D90=10min
D90=1min
The second one means that there is a reduction of 1 log in 1 min, and the top one means there is a reduction of 1 log in 10min.

21
Q

How does the composition of food affect D?

A 
Fat and CHO increase the resistance of the microorganism. 
ex. 
Salmonella spp. D70
6-8hr in chocolate milk
10seconds in low fat milk

FAT STABILIZES!

22
Q

D100 of 5 min.

explain after 5 min, 10 min and 15min

A

5min reduced by 90% (1 log)
10min reduced by 99% (2 log)
15min reduced by 3 logs

23
Q

What does Canning use for d value?

A

12D process

12 times.

24
Q 
D value caculations
ex. rate of inactivation= 1.5log/5min 
rate=slope= rise/run= y/x= log CFU/time
Rate=log CFU/time
1.5log/5min=1/x 
x=1/(1.5log/5min)
x=3.3min
D=3.3min
A

Shown on previous slide.

25
Q

Z value..what is it?

A

Expressed as temperature
It’s the change in temperature required for a thermal destruction curve to decrease one lo cycle in the same amount of time.
( relates to resistance of microorganism)

26
Q

z value in simple terms?

A

Change in temperature for 1 order of magnitude larger or smaller killing rate.

27
Q

Z value

  • Rate of killing is temperature dependent.
  • For a given system everything is constant EXCEPT time and temp.
  • Determined by the SLOPE of the thermal deat htime curce d value vs temperature
A

Keeping going, you got this.

28
Q

What is Z value dependent on?

A

Strain, and chemical composition of media

29
Q

Changing z value by 5C means?

A

That it kills factor of 10x faster.

30
Q

ex. At 100C originally needs 20 min.

What about at 105C and 95C

A

At 105 need 2min (for same rate of kill)
at 95 need 200min ( for same rate of kill)
- Worry about temp at which the microorganism will grow such as the danger zone 4.4-60C

31
Q

F value?

A

Time to reudce populaion by given amount in autoclave conditions ( 121C, 3psi)

32
Q

F0= Dr(loga-logb)
Dr= D value at temp 121C
a= initial population ( # of cells)
b=final population

A 
ex. 
Dr=0.45
initial population= 10^6
Final population = 10^1
F0=.45(log10^6-log10^1)
F0=.45(6-1)
F0=2.25min
33
Q

DEATH KINETICS

A

Usually plotted linear… however not in real conditions (done in plants!)
Shouldering and tailing

34
Q

What is shouldering? What causes it?

A

Shouldering is a lump at the start of the graph rather then linear.
It is causes by not even heating, clumping of organism so they are not evenly exposed to the heat.

35
Q

What is tailing and what causes it?

A

It is a tail of the graph and is caused by more resistant mutatnts, heat shock proteins.

36
Q

What is heat shock proteins?

A

Exposure to high temp for a short time could be induced. A stress response that allows cells to develop greter reistance to subsequent heat treatment.

37
Q

Heat shock proteins

A

seen at 60-70C, killed at 140C
|
(____________ kind of graph.

38
Q

cell injury ( sublethal injury)

A

Occurs when heating injures cell but doesn’t kill it.

  • Inability to grow in selective media ( doesn’t have the resources)
  • give time, restore viability and extend the lag phase.
  • STORAGE ALLOWS FOR REPAIR OF CELLS (BAAAAD)
39
Q

Sterilization..what is it?

A

Heating > 100C KILLS ALL CELLS, including endospores.
UHT (ultra-high temperature) 130C for sec (better on nutritional value)
Sterilization 121Cfor 15-20min

40
Q

What is the most resistant to sterilization?

A

Prototype.
bacillus stearothermophilus
Kill endospores at Dr 4 to 5min

41
Q

Pasteurization..what is it?

A

<100C
reduced numbers to safe levels
kill problem organisms

42
Q

What microorganisms are dangerous in milk?

A 
Mycobaterium tuberculosis (pathogen)
- D65.6 for 0.2-0.3min

coxiella burnetii
- Resistant to chemical and physical treatment.
D65.6=0.5-0.6min

43
Q

What are the two types of pasteurization?

A

LTH (Low temp holding) 63C for 30min

HTST (high temp, short time) 72C for 15sec

44
Q

What is an indicator organism in pasteurization?

A

Alkaline phosphatase
_ If not prsent we’ve killed pathogens we wanted to.
Z value similar to heath resistant pathogens.

45
Q

What is the process times of cooked meats?

A

Most pathogens killed if internal temp at >71C

  • Heating removes natural flora (stabilizes food)
  • Nitrites often included if meat stored anaerobically.

Food Microbiology (13 decks)

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