GROWTH OF LISTERIA-MONOCYTOGENES AND PSEUDOMONAS-FRAGI ON COOKED PORK IN A MODIFIED ATMOSPHERE PACKAGING NISIN COMBINATION SYSTEM

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-degrees-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-degrees-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 x 10(4) nisin IU/ml. In addition, the modified atmosphere packaging (MAP) (100% CO2, 80% CO2 + 20% air)/nisin (10(3), 10(4) 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-degrees-C than at 20-degrees-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.