Influence of packaging conditions on microbial and lipid oxidation in lamb meat

The effect of vacuum and three different modified atmospheres (MA) (A: 40% CO2/60% N2; B: 80% CO2/20% O2 and C: 80% CO2/20% N2) on rancidity, colour as CIE L* (lightness), a* (redness) and b* (yellowness) values, sensorial colour, sensorial odour and microbial content was studied in lamb meat. Longissimus dorsi samples were examined at 7-day intervals during storage at 2 °C. Rancidity increased with storage time in all four groups, but was more pronounced in B (with O2), and less in vacuum. Vacuum packaging conditions maintained a relatively optimum colour stability, while group B showed the highest L* and b*, and the lowest a* values. Sensory evaluation showed colour deterioration during storage in all groups, but was more marked in C. In MA treatments, lipid oxidation was significantly negative and positively correlated with a* and b* values, respectively. Unacceptable off-odours were first detected by panellists in B packs. Microbial growth was faster in vacuum packs, but after 28 days was similar in all treatments. Brochothrix thermosphacta was the predominant microbial group in MA, and lactic acid bacteria in vacuum.