HEAT RESISTANCE OF Pseudomonas aeruginosa IN PREPARATIONS AT THE BASE OF CUCUMBER, TOMATO AND LETTUCE AS AFFECTED BY PH AND SODIUM CHLORIDE

_____________________________________________________________________________ The effect of the acid and the osmotic stress on the heat resistance of Pseudomonas aeruginosa MC1 was studied at 63 oC in preparations at the base of cucumber, tomato and lettuce adjusted to various pHs (2, 3 and 4) or various NaCl concentrations (2, 4 and 6%). In the second study, the combined effect of pH and NaCl on the thermal inactivation of P. aeruginosa cells was determined. The heat resistance of P. aeruginosa cells was more rapid at pH 2 after 10 min of thermal shock for the three preparations. On the contrary, the heat resistance increased with increasing the pH values. At pH 3 or 4, viable cells were detected after 30 min of treatment when the cells inoculated in preparation of tomato. Addition of NaCl, was involved in the protection of cells against heat inactivation. Indeed, the best heat resistance of P. aeruginosa MC1 strain was obtained in tomato preparation supplemented with 4 or 6% of NaCl. This study indicates that heat resistance of Pseudomonas aeruginosa MC1 strain was lower at pH 2 and 2, 4 or 6% of sodium chloride. In addition, no viable cells were recovered after 1 min of treatment in lettuce preparation.