Some further data and thoughts about high pressure sterilization:
The pressures used are in the range of 1000 -10000 bar. Vegetative bacteria and yeasts
can be killed quite efficiently, especially in combination with mild heat ( e.g. 50°C).
Bacterial spores are very resistant. One approach to inactivate them is to apply cycles
of pressurization. Spore germination is induced by a first pressure shock, then the
outgrown spores can be killed by a second shock. This induction seems an interesting
phenomenon to me, but I don't know if the mechanism is the same as for heat-induced
germination.
The comparison with a French press is not fully valid, I think. In the latter, the cells
are forced through a narrow opening and must experience enormous shear forces, and
not only sudden decompression. Pressurization is just exposure to high hydrostatic
pressure in a closed container (e.g. vacuumized plastic bag). I think it has been shown
(I can find the reference if anybody is interested) that just the high constant pressure,
and the time that it is maintained, are responsible for most of the killing, not the
decompression rate.
About the mechanism, there are a lot of physiological effects that have been described
on eukaryotic cells, e.g. interference with transmembrane transport processes, changes
in the fluidity of lipid bilayers, dissociation of ribosomes. Less data are available on bacteria.
Protein denaturation by high pressure has also been extensively described and may
play a role.
Chris Michiels
