J. Raffalli et al., HIGH-PRESSURE STRESS AND INACTIVATION OF LISTERIA-INNOCUA IN INOCULATED DAIRY CREAM, Sciences des aliments, 14(3), 1994, pp. 349-358
Listeria innocua, ''model'' microorganism for Listeria monocytogenes w
as added to a liquid UHT dairy cream (35% fat) at a level of about 10(
7) CFU/ml. The cream was pressurized at 450 MPa and 25-26-degrees-C fo
r 10 to 30 min. The vegetative cells underwent alterations, some being
lethal, some others being reversible after a resuscitation step on a
nutritive broth at 37-degrees-C. For a pressurization time of 10 min,
microbial reduction reached 0.987 and 1.10(-5) of the initial cells gr
ew on a selective medium without a resuscitation step. With pressuriza
tion times of 20 and 30 min, microbial reduction reached 0.9995 and 0.
9999, respectively, all survivors being stressed (unable to grow on a
selective medium without a resuscitation step). Microbial inactivation
followed an apparent first order kinetics, with a decimal reduction t
ime of 7.4 min at 450 MPa (and 25-26-degrees-C). After 20 min under 45
0 MPa, a resuscitation step of 16 h at 37-degrees-C was necessary for
the growth of a maximum number of stressed bacteria.