EFFECTS OF THE KINETICS OF WATER POTENTIAL VARIATION ON BACTERIA VIABILITY

The effect of the kinetics of water potential variation (Psi) on the v iability of bacteria subjected to hyperosmotic stresses in water-glyce rol solution was studied. The three bacteria used were Lactobacillus p lantarum L-73, Leuconostoc mesenteroides LM057 and Escherichia coli TG 1. These strains were submitted to a final water potential of -107 . 2 MPa, -170 . 9 MPa and/or -244 . 7 MPa. In any case the kinetics of wa ter potential variation was found to have a great effect on the cell v iability. The application of slow water potential decreases could main tain an important cell viability (about 80-100%) with regard to the co rresponding viability observed after a sudden step change for the same final water potential (15-57%). For each strain tested, an optimal de hydration kinetics was determined which depended on the final water po tential. The existence of this optimum could be explained thanks to th e opposition of two actions affecting cell viability: a positive actio n relative to the slowness of the water potential variation and a nega tive action relative to the residence time of cells in a critical rang e of water potential.