Growth of Listeria monocytogenes and Pseudomonas fragi on Cooked Pork in a Modified Atmosphere Packaging/Nisin...

The influence of carbon dioxide (CO₂) atmospheres combined with various nisin concentrations on the growth of Listeria monocytogenes Scott A and Pseudomonas fragi CCRC 10939 on cooked tenderloin pork stored at 4 and 20°C was investigated. Atmospheres employed were 100 and 80% CO₂; and an air control. Pork tenderloins were steamed, cooled, and coinoculated with L. monocytogenes and P. fragi . Headspace composition of sample bags determined throughout storage at 4°C indicated that greater growth occurred on air-stored tenderloins than on modified atmosphere-stored (MA-stored) samples. Colony counts of P. fragi were appreciably reduced by the MA storage; however, the same pattern was not found in L. monocytogenes . Although P. fragi on cooked tenderloin was unaffected by nisin, the growth of L. monocytogenes was prevented when samples were treated with 1 × 10⁴ nisin IU/ml. In addition, the modified atmosphere packaging (MAP) (100% CO₂, 80% CO₂ + 20% air)/nisin (10³, 10⁴ IU/ml) combination system used in this study decreased growth of both organisms, and this inhibitory effect for MAP/nisin combination system was more pronounced at 4°C than at 20°C. The concept of a Safety Index, which compares numbers of spoilage and pathogenic organisms, was also used as a measure of the relative safety of this MAP/nisin combination system.