Microbial Destruction Kinetics Flashcards
What are the three main components destroyed/inactivated by heating?
- microbes
- enzymes
- nutrients
All spoilage/bacteria cultures are maintained by the ____ association
National Canner’s Association
How would a higher processing temperature affect D?
Shorter time needed for 1 D reduction (steeper slope)
Thermal destruction of microbes/enzyme/nutrients follow the ____ order reaction rate, with m = ___
first; m = 1
What does D represent?
Decimal reduction time; reduce bacterial population by 90%
The negative reciprocal of D is the slope on what graph?
time vs log concentration (at given temp)
Can the microbe population ever be reduced to zero, based on calculated kinetics?
Technically no; logarithmic reduction means it will never reach zero, but can be reduced to a tiny fraction (chance of spoilage)
True/False: heating a product over time will cause a linear decrease in the bacterial population
False; logarithmic curve
What does F represent? What is it used for?
Thermal Death Time; used for process calculations
Besides temperature, what else affects D value?
Bacteria type
The TDT and D curves, plotted vs temperature, have identical ____.
slopes
What does TDT refer to?
Thermal death time, minutes required to DESTROY a microbe at given temp.
True/False: TDT would not make sense in first order kinetics
True: TDT is time to completely destroy the microbes, which is theoretically impossible according to first order kinetics (log reductions)
Why might a bacteria have high D value?
Resistant to heat
True/False: D and TDT values depend on the initial bacteria concentration.
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)
What is destruction time?
between INITIAL TIME and NO SURVIVOR TIME (theoretically impossible)
the slope of the TDT and D curves (vs temp) signifies their ____ _____.
Temperature sensitivity
What is the z value?
indicator of TDT or D curve slope (temp sensitivity)
The shared slope of the TDT and D curves is expressed as:
-1/z
What are the pasteurization temperatures (in Fahrenheit?)
150, 180
What is the reference temperature for calculations (in Fahrenheit)?
250
What is MPN used in?
Stumbo’s thermoresistor approach for D
What are the calculation evaluation concepts used in TDT? (3)
- Plate count
- MPN (most probable number)
- End point technique
MPN is expressed as:
fraction (between zero and 1)
for given unit (can, mL, etc)
Describe the endpoint technique for TDT evaluation.
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
Name 3 experimental procedures for TDT evaluations
- Tube
- Can
- Thermoresister
How is the plate count method performed?
Prepare sample, compare initial count and final count (after heating)
*or can compare at T1 and T2
Calculate decimal reduction in time
The can technique is widely used in ____ ____ studies.
inoculated pack
What is used to provide heat for the tube and can experiments?
mini steam retorts
What are the dimensions of cans used for the TDT evaluation experiments?
208x006
Why are small tubes better for the tube technique?
Less heating lag
What are advantages of the tube technique?
- easy to subculture
- can observe growth
- inexpensive
- can do +/- or concentration count
What are advantages of the can technique?
- easy observation of swelling (+)
- mimics commercial conditions
- fast easy sealing
Which of the techniques has the least lag?
thermoresistor (no lag)
What are disadvantages of the thermoresistor?
high cost
cannot directly innoculate
The heating time for cans vs tubes will need adjustment due to:
heating and cooling lag
List the methods in order of increasing sample size
thermoresistor, tube, can
The thermoresistor can provide very precise ____ and ____.
time; temperature
MPN is determined using the ____ method.
thermoresistor
