Effects of the kinetics of water potential variation on bacteria viability

The effect of the kinetics of water potential variation (Psi) on the viability of bacteria subjected to hyperosmotic stresses in water-glycerol solution was studied. The three bacteria used were Lactobacillus plantarum L-73, Leuconostoc mesenteroides LM057 and Escherichia coli TG1. 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 water potential variation was found to have a great effect on the cell viability. The application of slow water potential decreases could maintain an important cell viability (about 80-100%) with regard to the corresponding viability observed after a sudden step change for the same final water potential (15-57%). For each strain tested, an optimal dehydration kinetics was determined which depended on the final water potential. The existence of this optimum could be explained thanks to the opposition of two actions affecting cell viability: a positive action relative to the slowness of the water potential variation and a negative action relative to the residence time of cells in a critical range of water potential.