The successof hurdletechnologydepends onensuring metabolicexhaustion. Moststressreactionsof
microorganisms are activeprocesses, and thisoften involves the expenditureofenergy,e.g.totransportprotonsacross
the cell membrane, to maintainhighcytoplasmic concentrationsof ‘osmoregulatory’or ‘compatible’solutes.
Restriction of the availabilityof energyis then a sensible target to pursue. This probably forms the basis ofmanythe
successful, empirically derived, mildcombination preservation procedures exemplified by hurdletechnology.
As anexample, if a food can bepreserved by lowering the pH, then it is sensible also toincludea weak acid preservative which will amplify the effect of the protons or toallow amilder,higher pHto beemployed. Itissensibleif
protonexportis made more difficult by the additional requirement that cells be forcedtoregulate osmoticstrength.
Then, if the foodcan beenclosedin oxygen-free vacuumor modifiedatmosphere packaging, facultative anaerobes will
be further energy-restricted at a timewhen the various stress and homeostatic reactions are demanding more energyif
growthis to proceed.