Research issues in inactivation of Listeria monocytogenes associated with New Zealand Greenshell mussel meat (Perna canaliculus) using high-pressure processing

New Zealand Greenshell mussels are currently shucked by heat processing, and this can be used as a listericidal step. Shucking by high pressure processing (HPP) has potential benefits in product quality and increased yield, but processors need to understand the effects of this technology on the safety of their product with respect to Listeria monocytogenes. L. monocytogenes was mixed with minced mussel meat, and 2 g samples (in foil pouches) were subjected to HPP at various pressures, times, and temperatures. Of 10 tested strains of L. monocytogenes, the most resistant to HPP at 400 MPa (Food Science Australia strain 2655 isolated from Australian processed meat) was selected for subsequent work. This strain showed two-phase inactivation kinetics in response to time at 400 MPa. Approximately 5 log(10) cells/g were rapidly inactivated in a log-linear fashion with time while the remaining cells were inactivated at a slower rate. There was also some evidence of a shoulder in the inactivation curves. In the temperature range tested (10 degrees C-40 degrees C), the log-linear inactivation rates showed linear increases with increasing processing temperature at 400 MPa with a z value of 29.1 min.