Beef shelf life in low O(2) and high CO(2) atmospheres containing different low CO concentrations

The use of atmospheres with low concentrations of CO (0.1 to 1%), in combination with O₂ (24%), high CO₂ (50%) and N₂ (25 to 25.9%), for preserving chilled beef steaks was investigated. The atmosphere used as reference contained 70% O₂+20% CO₂+10% N₂. Bacterial counts showed that all atmospheres containing CO greatly reduced total aerobic population numbers, including Brochothrix thermosphacta. Lactic acid bacteria, however, were not affected. CO concentrations of 0.5–0.75% were able to extend shelf life by 5–10 days at 1±1°C, as demonstrated by delayed metmyoglobin formation (less than 40% of total myoglobin after 29 days of storage), stabilisation of red colour (no change of CIE a* and hue angle after 23 days), maintenance of fresh meat odour (no variation of sensory score after 24 days) and significant (P<0.01) slowing of oxidative reactions (TBARS).