Influence of modified atmospheric storage, lactic acid, and NaCl on survival of sublethally heat-injured Listeria monocytogenes

The effect of package atmosphere on survival of uninjured and sublethally heat-injured Listeria monocytogenes, inoculated onto tryptose phosphate agar containing 0.85% lactic acid and 2% NaCl (TPALAS) was investigated. Inoculated TPALAS plates were packaged in air, 100% N-2 (N-2), 30% CO2-70% N-2 (CO2-N-2), and vacuum and stored at 4 and 20 degreesC for up to 31 days. Recovery of L. monocytogenes from TPALAS was influenced by the injury status (i.e., injured and uninjured) of the inoculum, storage atmosphere (air, N-2, CO2-N-2, and vacuum), storage temperature (4 and 20 degreesC), and recovery media [tryptose phosphate agar (TPA) and modified Oxford agar (MOX)] (P < 0.05). Overall, storage at 4C supported greater survival than storage at 20 degreesC (P < 0.05). Uninjured L. monocytogenes stored at 4C was recovered on TPA better than sublethally heat-injured L. monocytogenes stored at 4 degreesC (P < 0.05). Recovery of sublethally heat-injured L. monocytogenes stored at 4C followed the order N-2 > CO2-N-2 > air > vacuum (P < 0.05), whereas recovery of uninjured L. monocytogenes stored at 4C followed the order N-2 > CO2-N-2 > vacuum > air (P < 0.05). Air and vacuum atmospheres supported greater survival of uninjured and heat-injured L. monocytogenes than N-2 and CO2-N-2 atmospheres at 20C (P < 0.05), Recovery of sublethally heat-injured L. monocytogenes stored at 20C followed the order vacuum > air > CO2-N-2 = N-2 (P < 0.05), whereas recovery of uninjured L. monocytogenes stored at 20C followed the order vacuum > air > CO2-N-2 > N-2 (P < 0.05). Uninjured L. monocytogenes stored under N-2 at 4C was recovered best, whereas sublethally heat-injured L. monocytogenes stored under N-2 at 20 degreesC was recovered poorest (P < 0.05). Factors such as package atmosphere and storage temperature, involved in the production, storage, and distribution of fermented foods must be thoroughly evaluated when determining strategies for control and detection of L. monocytogenes in such products. <(c)> 2001 Elsevier Science BSI. All rights reserved.