CONTINUED INHIBITORY EFFECT OF CARBON-DIOXIDE PACKAGING ON LISTERIA-MONOCYTOGENES AND OTHER MICROORGANISMS ON NORMAL PH BEEF DURING ABUSIVERETAIL DISPLAY

Beef steaks of normal pH (5.3-5.5) were inoculated with Listeria monoc ytogenes, individually packaged in saturated carbon dioxide atmosphere packaging (SCAP) for <3 h or 5 or 8 weeks or in vacuum packaging (VP) for <3 h, and stored at -1.5 degrees C. After each storage period, 27 individually packaged steaks were removed from their storage packs, o verwrapped and placed on retail display under conditions simulating gr oss temperature abuse (12.25 degrees C). Other steaks were removed fro m their storage packs and rinsed to remove L. monocytogenes cells, whi ch were re-inoculated onto freshly cut beef steaks to simulate cross-c ontamination These cross-contaminated steaks were overwrapped and also subjected to abusive display. Meat pH did not change significantly du ring storage or retail display. During the retail display of steaks pr eviously stored in SCAP, the lag phase of aerobic bacteria and lactic acid bacteria was longer after prolonged storage compared to short (<3 h) exposure to carbon dioxide. For the same samples, L. monocytogenes failed to grow during retail display or grew only slightly after a pr olonged lag phase (>75 h), even after only brief exposure time (<3 h) to carbon dioxide. In contrast, with cross-contaminated steaks, when t he inocula had been exposed to SCAP or VP for a short time (<3 h) the L. monocytogenes lag phase was shorter (<20 h). Inocula from steaks st ored in SCAP for 5 or 8 weeks did not grow on the cross-contaminated s teaks. It is concluded that exposure of both the beef substrate and th e L. monocytogenes inoculum to carbon dioxide during prolonged chilled storage does not increase the risk of growth of L. monocytogenes when that meat is subsequently placed on retail display, nor is there a la rge risk of growth of L. monocytogenes where cross-contamination from SCAP stored raw beef to fresh raw beef occurs prior to retail display.