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

The influence of carbon dioxide (Co2) atmospheres combined with variou s 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, a nd coinoculated with L monocytogenes and P. fragi. Headspace compositi on of sample bags determined throughout storage at 4-degrees-C indicat ed that greater growth occurred on air-stored tenderloins than on modi fied 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 tenderlo in was unaffected by nisin, the growth of L monocytogenes was prevente d when samples were treated with 1 x 10(4) nisin IU/ml. In addition, t he modified atmosphere packaging (MAP) (100% CO2, 80% CO2 + 20% air)/n isin (10(3), 10(4) IU/ml) combination system used in this study decrea sed growth of both organisms, and this inhibitory effect for MAP/nisin combination system was more pronounced at 4-degrees-C than at 20-degr ees-C. The concept of a Safety Index, which compares numbers of spoila ge and pathogenic organisms, was also used as a measure of the relativ e safety of this MAP/nisin combination system.