D value L15 Flashcards
what happens during minimum growth rate
membranes gelling, transport processes so slow that growth cant occur
what happens during the time between minimum growth and optimum growth
enzymes and reaction occurring at increasingly rapid rates
what happens at optimum growth
enzymes and reactions occurring at maximal possible rate
what happens at maximum growth
protein denaturation, collapse of the cytoplasmic membrane, thermal lysis
when are cells thermally inactive
When cells are exposed to temperatures above their µmax value, irreversible cell damage occurs
what is µmax
maximum growth temperature
what is autoclaving used for
sterilising things
what are death rates like
irrespective of temperature, death rates are not linear
Populations of cells are not identical and some are more resistant to heat than others
if a log of death rate is plotted what is the graph like
linear graph
The slope of this line can be used to predict the time required to kill a population of cells at a given temperature
what is the D value represent
time takes to destroy 90% of the starting population
how is the D value determined
by plotting graph of log10 [viable cells remaining] vs time
what is the D value independent of
initial microbial load:
i.e. if starting numbers are high, residual numbers will also be high
what does a log 10 drop in population mean
a loss of 90% of the viable cells
in the first three log 10 drops what is the percentage at each stage that is killed
first =90%
second = 99%
third =99.9%
to kill 10^4 cells how long when they need heat treatment
you expose for at least 4 x D
4 decimal reductions in population required
5D would normally be used to ensure all cells killed
