The effects of residual oxygen concentration and temperature on the degradation of the colour of beef packaged under oxygen-depleted atmospheres.

Samples of beef longissimus dorsi (LD), approximately 5 × 5 × 1 cm, were packaged in pairs under 10 litre volumes of N(2) or CO(2) containing O(2) at concentrations between 100 and 1000 ppm. The packaged samples were stored at temperatures of 5, 1, 0 or -1·5°C, for times between 4 and 48 h. Samples of beef psoas major (PM) were packaged under N(2) or CO(2) containing O(2) at between 100 and 600 ppm, and stored at -1·5°C for 24 or 48 h. After storage, each sample was assessed for colour deterioration and discoloration, and for the fraction of metmyoglobin in the surface pigment. The results obtained with N(2) and CO(2) atmospheres were similar. The colours of all LD samples had deteriorated after 4 h storage at 5 or 1°C, although the degree of deterioration increased with increasing O(2) concentration. All LD samples stored for 12 h at 5 or 1°C were extensively discoloured, with metmyoglobin fractions generally exceeding 60%, but those stored at -1·5°C for 48 h or less, under O(2) concentrations ≤ 400 ppm had undergraded colours. The colours of some LD samples stored at -1·5°C under about 600 ppm of O(2) were also undergraded, but the colours of samples stored under 800 or 1000 ppm had deteriorated by 24 h. The colours of LD samples stored at 0°C under > 200 ppm had deteriorated after 24 h storage, and the colours of samples stored under 100 ppm O(2) had deteriorated after 48 h storage. All PM samples were wholly discoloured after storage at -1·5°C. Evidently, the colour of beef muscle of high colour stability is resistant to degradation by atmospheres containing < 600 ppm of O(2) when the meat is stored at sub-zero temperatures, but not when the storage temperature is at or above 0°C. Beef muscle of low colour stability, such as the PM, will discolour at all low concentrations of O(2) irrespective of the storage temperature.