High pressure inactivation of citrobacter freundii, pseudomonas fluorescens and listeria innocua in inoculated minced beef muscle

Abstract

Fresh minced beef muscle inoculated with Citrobacter freundii, Pseudomonas fluorescens or Listeria innocua was subjected to high hydrostatic pressures from 50 to 400 MPa for 20 min at 4, 20, 35 and 50°C. At 20°C, complete inactivation (more than 5 log cycles) was observed at pressures above 200 MPa for P. fluorescens, above 280 MPa for C. freundii and above 400 MPa for L. innoccua. Higher (50 or 35°C) or lower (4°C) temperatures enhanced the effects of pressure. The greatest reduction was obtained at 50°C. At a given pressure, surviving microorganisms decreased exponentially with time, and a decimal reduction time could be calculated for each microorganism (23.8 min at 150 MPa for P. fluorescens, 14.7 min at 230 MPa for C. freundii and 6.5 min at 330 MPa for L. innocua). Partial discoloration of meat was observed after 10 min pressurization above 150 MPa. Minced beef muscle lost its red colour and became grey after 10 min pressurization above 350 MPa. © 1993 Academic Press Limited.