Inactiviation of microorganisms by high pressure

Abstract

Microbial inactivation by high pressure is, in many respects, comparable to heat: the inactivation kinetics are the same and both heat and pressure can induce sublethal damage of the cells, reflected by a prolonged lag time. Bacterial cells are more sensitive to pressure and to heat at low pH and a low water activity gives the same protection for cells against pressure as it does against heat. We have shown that carbohydrates protect cells against pressure in the order trehalose > sucrose > glucose > fructose > glycerol. The membrane protective effect of these sugars is also in this order. There is also sufficient circumstantial evidence that the composition of the membrane correlates with resistance to pressure. The inactivation patterns of proteins and bacteria by pressure are quite similar and therefore it is reasonable to assume that inactivation of enzymes plays a role in pressure inactivation. We have therefore focused our attention on the membrane. After pressure treatment the intracellular pH could not be maintained at the same level as in untreated cells. This might be due to damage to the glycolytic pathway or inactivation of membrane bound enzymes, for example F₀F₁, ATPase. We have not yet investigated the effects of pressure on the glycolytic pathway. F₀F₁ ATPase was inactivated at high pressure. The latter observation suggests that membrane bound proteins would be involved in high pressure inactivation.