Lecture 4: Microbial Destruction Kinetics Flashcards Preview

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Flashcards in Lecture 4: Microbial Destruction Kinetics Deck (23)
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1
Q

in the thermal destruction of microbes, enzymes and nutrients follow what reaction rate?

what equation represents this?

A

first order rxn rate

-[dC/dt] = kC

2
Q

in the plot of log C vs t, what represents the intercept?

A

intercept = logCo

3
Q

in the plot of log C vs t, what represents the slope?

A

slope = -k/2.303

4
Q

what is FS?

A

flat sour

a type of microorganism that causes spoilage

5
Q

what is the difference between FS and other spoilage microorganisms?

A

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

6
Q

what is D?

A
  • 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
7
Q

what is Co?

A

microbial concentration at time t0

8
Q

what is k?

A

reaction rate

9
Q

what is TDT?

A

thermal death time

the time in minutes required to destroy a microbial population at any given temperature

used exclusively in in process calculations

10
Q

what is the destruction time set between?

A

initial time and no-survivor time

11
Q

death time depends on _____

A

initial population (higher population means longer TDT)

12
Q

how are TDT and D related?

A
  • 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
13
Q

complete destruction is ____

A

theoretically impossible

14
Q

what indicates the temperature sensitivity of TDT (or D) vs T graph?

A

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

15
Q

what is the z value?

A
  • 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
16
Q

how can you calculate the z value from the slope of logTDT vs temp?

A

slope = -1/z

17
Q

what is the reference D value?

A

Do

18
Q

what is the reference k value

A

ko

19
Q

what is the sterilization reference temp?

A

250degF or 121degC

20
Q

what is the pasteurization reference temp?

A

150degF or 180degC

21
Q

what is N and No?

A
N = final count of microorganisms
N0 = initial count
22
Q

what is MPN

A

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
23
Q

what is the MPN equation used in?

A

stumbo’s thermoresistor approach for D

to determine initial and final counts