INHIBITION OF LISTERIA-MONOCYTOGENES ON NORMAL ULTIMATE PH BEEF (PH 5.3-5.5) AT ABUSIVE STORAGE TEMPERATURES BY SATURATED CARBON-DIOXIDE CONTROLLED-ATMOSPHERE PACKAGING

Beef striploin steaks (each weighing between 60 and 100 g) of normal ultimate pH (average 5.45) were inoculated with a mixture of two food isolates of Listeria monocytogenes, packaged under saturated carbon dioxide controlled atmosphere or vacuum, and stored at either 5 or 10-degrees-C. Saturated carbon dioxide packaging but not vacuum packaging inhibited growth of L. monocytogenes. During storage under vacuum at 5-degrees-C, numbers increased from 6.2-log10 CFU per sample to 9.0-log10 CFU per sample in 23 days, and at 10-degrees-C numbers increased from 6.3-log10 CFU per sample to 9.5-log10 CFU per sample in 11 days. During storage under saturated carbon dioxide at 5-degrees-C, numbers decreased from 5.6-log10 CFU per sample to 5.0-log10 CFU per sample in 18 days, and at 10-degrees-C numbers decreased from 6.7-log10 CFU per sample to 5.2-log10 CFU per sample in 44 days. The use of saturated carbon dioxide controlled atmosphere packaging to extend the storage life of fresh beef results in apparent destruction of L. monocytogenes even at abuse temperatures.