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)
