Psychrotrophy and foodborne Salmonella

Recent reports on the behaviour of Salmonella at chill temperatures (less than 10 degrees C) raise concerns on the purported safety of refrigerated foods. The propensity for growth of salmonellae within 10-28 days in complex broth (5.9 degrees C) and agar (4.0 degrees C) media is overshadowed by more recent evidence on their capability to proliferate in fresh meats (2.0 degrees C) and shell eggs (4.0 degrees C) within 6 and 10 days, respectively. Such findings, together with the inability of many domestic refrigerators to maintain uniformly cold temperatures, are disquieting. Gaseous mixtures of CO2, N2 and O2 are widely used to extend the shelf life of chilled foods, notably fresh meats. The high levels of CO2 used in modified atmosphere packaging or generated by endogenous microflora in vacuum-packaged foods effectively inhibit the growth of psychrotrophic spoilage bacteria. Current evidence suggests that this industrial practice also arrests the growth of Salmonella but exerts little or no effect on their survival. Enhancement of the bacteriostatic potentials of pH and NaCl as temperature deviates from the optimum for growth to lower values could further contribute to the safety of chilled foods.