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food processing > Microbial Destruction Kinetics > Flashcards

Microbial Destruction Kinetics Flashcards

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1
Q

What are the three main components destroyed/inactivated by heating?

A
  • microbes
  • enzymes
  • nutrients
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2
Q

All spoilage/bacteria cultures are maintained by the ____ association

A

National Canner’s Association

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3
Q

How would a higher processing temperature affect D?

A

Shorter time needed for 1 D reduction (steeper slope)

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4
Q

Thermal destruction of microbes/enzyme/nutrients follow the ____ order reaction rate, with m = ___

A

first; m = 1

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5
Q

What does D represent?

A

Decimal reduction time; reduce bacterial population by 90%

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6
Q

The negative reciprocal of D is the slope on what graph?

A

time vs log concentration (at given temp)

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7
Q

Can the microbe population ever be reduced to zero, based on calculated kinetics?

A

Technically no; logarithmic reduction means it will never reach zero, but can be reduced to a tiny fraction (chance of spoilage)

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8
Q

True/False: heating a product over time will cause a linear decrease in the bacterial population

A

False; logarithmic curve

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9
Q

What does F represent? What is it used for?

A

Thermal Death Time; used for process calculations

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10
Q

Besides temperature, what else affects D value?

A

Bacteria type

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11
Q

The TDT and D curves, plotted vs temperature, have identical ____.

A

slopes

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12
Q

What does TDT refer to?

A

Thermal death time, minutes required to DESTROY a microbe at given temp.

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13
Q

True/False: TDT would not make sense in first order kinetics

A

True: TDT is time to completely destroy the microbes, which is theoretically impossible according to first order kinetics (log reductions)

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14
Q

Why might a bacteria have high D value?

A

Resistant to heat

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15
Q

True/False: D and TDT values depend on the initial bacteria concentration.

A

False;
D values are the same regardless of initial C (decrease at constant log rate)
TDT values will be larger for larger initial concentrations (need longer time to bring to 0)

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16
Q

What is destruction time?

A

between INITIAL TIME and NO SURVIVOR TIME (theoretically impossible)

17
Q

the slope of the TDT and D curves (vs temp) signifies their ____ _____.

A

Temperature sensitivity

18
Q

What is the z value?

A

indicator of TDT or D curve slope (temp sensitivity)

19
Q

The shared slope of the TDT and D curves is expressed as:

A

-1/z

20
Q

What are the pasteurization temperatures (in Fahrenheit?)

A

150, 180

21
Q

What is the reference temperature for calculations (in Fahrenheit)?

A

250

22
Q

What is MPN used in?

A

Stumbo’s thermoresistor approach for D

23
Q

What are the calculation evaluation concepts used in TDT? (3)

A
  • Plate count
  • MPN (most probable number)
  • End point technique
24
Q

MPN is expressed as:

A

fraction (between zero and 1)

for given unit (can, mL, etc)

25
Q

Describe the endpoint technique for TDT evaluation.

A

Prepare samples for different time intervals, determine if viable growth afterwards
Use data for longest survival time and shortest destruction time
Interpolate to determine TDT

26
Q

Name 3 experimental procedures for TDT evaluations

A
  1. Tube
  2. Can
  3. Thermoresister
27
Q

How is the plate count method performed?

A

Prepare sample, compare initial count and final count (after heating)
*or can compare at T1 and T2
Calculate decimal reduction in time

28
Q

The can technique is widely used in ____ ____ studies.

A

inoculated pack

29
Q

What is used to provide heat for the tube and can experiments?

A

mini steam retorts

30
Q

What are the dimensions of cans used for the TDT evaluation experiments?

A

208x006

31
Q

Why are small tubes better for the tube technique?

A

Less heating lag

32
Q

What are advantages of the tube technique?

A
  • easy to subculture
  • can observe growth
  • inexpensive
  • can do +/- or concentration count
33
Q

What are advantages of the can technique?

A
  • easy observation of swelling (+)
  • mimics commercial conditions
  • fast easy sealing
34
Q

Which of the techniques has the least lag?

A

thermoresistor (no lag)

35
Q

What are disadvantages of the thermoresistor?

A

high cost

cannot directly innoculate

36
Q

The heating time for cans vs tubes will need adjustment due to:

A

heating and cooling lag

37
Q

List the methods in order of increasing sample size

A

thermoresistor, tube, can

38
Q

The thermoresistor can provide very precise ____ and ____.

A

time; temperature

39
Q

MPN is determined using the ____ method.

A

thermoresistor

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