In my message from oct 4th (Re:Re:high pressure sterilization), I promised that,
upon request, I would dig up a reference where it is shown that the killing effect of
pressurization stems from the high pressure that is maintained during some time,
rather than from the sudden decompression at the end of the pressurization. I got
an E-mail request already, so here is the answer for those interested. I can see two
types of evidence:
1. Bacterial counts decrease with the time they are held at a constant (high) pressure.
Some authors found that the inactivation follows a first order kinetics, meaning that a
constant fraction of the population is inactivated every minute. This is also the case
for heat inactivation. You can find this in many articles about high pressure inactivation,
a good review is: Heden (1964), Bacteriological Reviews 28:14-29; a more recent study:
Styles et al. (1991), J. Food Sci. 56:1404-1407.
2. The reduction in counts for a single pressure treatment during 1h was approximately
the same as for 12 consecutive 5-minute cycles at the same pressure. In the first case,
there is only one decompression, in the second case 12. See: Sale et al. (1970),
J. Gen. Microbiol. 60:323-334.
I must admit that in none of these studies the actual decompression rate is measured. I am
not aware of studies that have tackled this issue, but would be interested to hear if anybody is.
So I do NOT say that microorganisms are insensitive to sudden decompression, but to kill
them, it will probably have to be real fast.
Chris Michiels
K.U.Leuven, Belgium
