ABSTRACT
Aims: To investigate the effect of pressure, pressurization time, pressurization temperature and their interaction on inactivation and recovery of Listeria innocua inoculated in minced chicken meat. Study Design: Effect of the parameters of high pressure processing (HPP) on the inactivation of L. innocua were studied by response surface methodology using Box- Behnken design. Place and Duration of Study: Study conducted during an 11 months postdoctoral study at Agriculture, Agronomy and Food Sciences Department at LUNAM Université, Oniris, Nantes, France. Methodology: Minced chicken meat inoculated with Listeria innocua strain ATCC 33090 to give a total aerobic count (TAC) of 108 cfu/g and samples were subjected to high pressures of 200, 300, 400 MPa, temperatures of 0ºC, 20ºC, 40ºC and holding times of 5, 10 and 15 minutes. Survival of L. innocua was determined by TAC immediately after pressure treatment and during 35 days of storage at 3ºC. Results: Survival of L. innocua decreased with increasing pressure and pressurization time. Effect of pressurization temperature on survival of bacteria was not linear, giving higher reduction at 0ºC and 40ºC compared to treatments at 20ºC. Analysis of variance (ANOVA) showed that pressure (P<.001), time (P<.001), temperature (P=.05) and interaction of pressure and temperature (P=.05) were significant parameters. After a 10 min treatment at 400 MPa and 0ºC, no survival of microorganisms was detected immediately after pressure treatment. However, TAC increased during storage and reached to about the initial level of microbial load (108cfu/g) in all samples after 35 days of storage at 3ºC. Conclusion: Undetected survival of microorganisms in a nutrient rich food immediately after a pressure treatment does not necessarily mean total inactivation of the microorganisms. Injured microbial cells could recover during the refrigerated storage and compromise the safety of pressure treated foods. Therefore, care must be taken to ensure the safety of high pressure processed foods.