Definitions/Calculations Flashcards
What is the D-value?
Time required to kill 90% of organisms
- Time for 1 log reduction (10 fold)
- Can be used for both heat and radiation
The higher the D-value…
The more resistant the bacterium
What is the Z-value?
The temperature increase needed to reduce the D-value by 90%
- 1 log reduction (10 fold)
- The temp increase that will result in the bacteria being kill 10x faster
- Plot LogD and then read 10 then 1 (then calc difference)
Sterilisation processes are often based on what kind of scenario?
Worse-case scenario
IF =
IF = N0/Nt
IF = 10^t/D
What are the 3 stages in a temperature profile of a sterilisation process?
Heating stage
Holding stage
Cooling stage
Which two stages in a temperature profile contribute to sterilisation?
Heating and Cooling stages
What is the F-value?
Expresses lethality of heat treatment at any temperature equivalet to treatment at a reference temperature
Expressed in minutes
Only used if temp is the only influencing factor
How do you calculate Q10?
(Time to kill at Temp (C))/(Time to kill at Temp+10 (C))
In n sampes, what is the probability of all being non-infected (passing sterility test)?
q^n
What is k?
Inactivation rate constant (k=2.303/D)
What is Q10?
Change in k from a 10 degree change in temperature
What is IF?
Measure of total microbial inactivation
What is F0?
Equivalent time of moist sterilisation at 121C, which a z value of 10C
What is PNSU?
Probability of a non-sterile unit
