High pressure inactivation kinetics of bacillus subtilis cells by a three‐state‐model considering distributed resistance mechanisms

Abstract

Inactivation of vegetative Bacillus subtilis ATCC 9372 by high hydrostatic pressure treatment (200 ‐ 450 MPa) was tested at 20, 30 and 40°C. Time ‐ inactivation curves of the bacteria suspended in Ringer's solution showed sigmoid asymmetric shapes when plotted in logarithmic scale. Kinetic analysis of the survivor data was performed by fitting a two‐step‐model. It was assumed that during pressure treatment, the bacterial cells pass through a metastable intermediate state which is reached after endogenous homeostatic mechanisms balancing the pressure induced displacements of equilibria can no longer be maintained. Combined pressure‐temperature‐pH effects may target this state and cause lethal cell damage. Modelling this concept, a distributive function describing the initial transition was used in combination with a first‐order reaction which was assumed to govern the irreversible second step. Regressively derived characteristic parameters showed logarithmic‐linear behaviour. Applicability of the model on dynamic treatments with constant rate of pressure increase could be proven.