Lecture 4: Microbial Destruction Kinetics Flashcards
in the thermal destruction of microbes, enzymes and nutrients follow what reaction rate?
what equation represents this?
first order rxn rate
-[dC/dt] = kC
in the plot of log C vs t, what represents the intercept?
intercept = logCo
in the plot of log C vs t, what represents the slope?
slope = -k/2.303
what is FS?
flat sour
a type of microorganism that causes spoilage
what is the difference between FS and other spoilage microorganisms?
when FS is active, it doesn’t produce gas (it only produces acidity). Thus, the presence of FS does not cause bulging of a can
however, when other microorganisms are active, this causes gas production, which results in bulging of the can
what is D?
- decimal reduction time
- a heating time at any given temperature that results in:
1. 90% destruction of the microbial population
or
2. one decimal reduction in the surviving population
what is Co?
microbial concentration at time t0
what is k?
reaction rate
what is TDT?
thermal death time
the time in minutes required to destroy a microbial population at any given temperature
used exclusively in in process calculations
what is the destruction time set between?
initial time and no-survivor time
death time depends on _____
initial population (higher population means longer TDT)
how are TDT and D related?
- TDT represents a multiple of D value (shown by: TDT = nD and their parallel slopes)
- TDT and D also vary semi-logarithmically with temperature (they
complete destruction is ____
theoretically impossible
what indicates the temperature sensitivity of TDT (or D) vs T graph?
the negative slope
therefore, when temperature increases, D or TDT value decreases.
A steeper slope means higher temperature sensitivity
A less steep slope means less temperature sensitive
what is the z value?
- the temperature range between which TDT or D value curve passes through one log cycle
- the slope indicator of TDT curve or D value curve
- negative reciprocal slope of the regression line
how can you calculate the z value from the slope of logTDT vs temp?
slope = -1/z
what is the reference D value?
Do
what is the reference k value
ko
what is the sterilization reference temp?
250degF or 121degC
what is the pasteurization reference temp?
150degF or 180degC
what is N and No?
N = final count of microorganisms N0 = initial count
what is MPN
most probable number per given unit
MPN = (2.303/a) log (n/q)
a = amount of sample n = total # of replicates q = number of negative samples
what is the MPN equation used in?
stumbo’s thermoresistor approach for D
to determine initial and final counts
