Résumé
Smoked salmon mince inoculated simultaneously with Listeria innocua, Micrococcus luteus and Pseudomonas fluorescens was subjected to different pressure–temperature conditions. Control freeze–thaw at 0.1MPa with storage at −15°C or −40°C for 0–5 days did not induce microbial inactivation. Control pressurisation at 207MPa for 23min at 20°C (initial sample temperature) with fast (3s) pressure release had no significant effect on Gram+bacteria while P. fluorescens underwent a 2.8 log cycle reduction. Pressurisation at 207MPa for 23min at −3°C (without ice crystal formation) enhanced microbial reduction to 3.8 log cycles for P. fluorescens and to about 0.5 log cycle for Gram+bacteria. “Pressure-shift nucleation” (PSN) from 207MPa and −21°C (i.e. cooling at 207MPa for 23min followed by pressure release in 3s) caused 1.2, 1.4 and 4.3 log cycle reductions of L. innocua, M. luteus and P. fluorescens, respectively. A reduction of 1.7 log cycle was observed for L. innocua and M. luteus (4.6 log cycle for P. fluorescens) when salmon mince was subjected to pressure-shift freezing (PSF) (i.e. PSN from 207MPa and −21°C as above followed by further freezing to −25°C at 0.1MPa). PSF with pressure release in 18min enhanced reduction to 2 and 2.5 log cycles for L. innocua and M. luteus, respectively.