The effect of ageing treatment on the microbiology and storage characteristics of beef in modified atmosphere packs containing 25% CO(2) plus 75% O(2).

The influence of different ageing treatments (1 week hung in air; 1 and 3 weeks in vacuum packs) on the microbiological, colour, odour and rancidity characteristics of beef loin steaks during storage at 1° and 6°C in modified atmosphere packs (MA) containing 25% CO(2) + 75% O(2) was determined. Steaks from the 3-week ageing treatment discoloured more rapidly and developed off-odours sooner than those from the 1-week ageing treatments at both storage temperatures. Evidence of rancidity, using the thiobarbituric acid assay, was only observed in the 3-week aged steaks stored at 6°C. The poorer storage stability of the 3-week aged steaks was explained by higher initial levels of bacteria resulting from growth during ageing. Leuconostocs were the dominant bacteria on most MA samples following storage and appeared the main cause of spoilage, although B. thermosphacta and Pseudomonas spp may have contributed to off-odours on samples aged hung and stored at 6°C.