Microbial Flora of Normal and High pH Beef Stored at 4 C in Different Gas Environments

Beef of high pH (6.6) and of normal pH (5.8) was packed in air, a mixture of 78% N₂ + 20% CO₂ + 2% 0_2, vacuum, and 100% CO₂ and stored at 4 C. The effect of the different gas environments on development of the microbial flora of the two types of beef was examined. The shelf-life increased in the order: pure CO₂ > vacuum > gas mixture (20% CO₂ > air. After storage in air for 14 days, Pseudomonas spp. comprised 76% of the flora on the normal beef and 88% of the flora on the high pH beef. In the gas mixture, after 21 days the microbial flora on the normal beef was dominated by lactic acid bacteria (52%), Enterobacteriaceae (16 %) and coryneforms (16 %) while the high pH beef contained Pseudomonas spp. (44 %), lactic acid bacteria (28%) and Brochothrix thermosphacta (28%). In the vacuum, after 21 days 96% of the flora in normal beef consisted of lactic acid bacteria, whereas 60% lactic acid bacteria and 40% B. thermosphacta were found on the high pH beef. In pure CO_2, stored for 51 days, both the normal and high pH beef were completely dominated by lactic acid bacteria.