Anaerobic microbiology of fresh beef packaged under modified atmosphere or vacuum

Beef was packaged under CO2 containing 500 PPM O2 (MAP), vacuum, or air and stored at 0, 2, or 4 degrees C. Samples were analyzed weekly for bacterial numbers using anaerobic plate count (pre-reduced medium and anaerobic chamber), aerobic plate count, and anaerobic jar plate count (MAP samples only) methods. For both MAP and vacuum packaged samples, the anaerobic plate count was consistently greater than the aerobic plate count and for MAP samples the anaerobic plate count was consistently higher than the anaerobic jar plate count. Differences between plating methods were most frequent during the latter third of 0 and 2 degrees C storage. Anaerobic isolates from MAP samples were most often lactic acid cocci and staphylococci. No clostridia were isolated from any of the treatments