Boneless pork roasts were vacuum-packaged; one group remained in vacuum-packages (controls), other vacuum-packages were injected with one of six gas mixtures: (a) 100% O2, (b) 20% CO2 + 80% N2, (c) 50% CO2 + 50% O2. (d) 20% CO2 + 80% O2, (e) 25% CO2 + 25% O2 + 50% N2, or (f) 51% CO2 + 30% O2 + 18% N2 + 1% CO. Roasts were stored from 0–35 days at 1–3 C and chops from each treatment were observed under retail conditions for 5 days. Differences, both in psychrotrophic and lactobacillus counts, between roasts stored in modified gas atmospheres and those stored in vacuum-packages were rarely statistically significant. Psychrotrophic counts of pork chops from roasts stored for 21–35 days in modified gas atmospheres were somewhat higher than those prepared from comparable vacuum-packaged roasts. However, few of these differences were statistically significant. The initial microbial flora of the roasts consisted of Pseudomonas and Lactobacillus spp. Pseudomonas spp. remained a significant part of the microflora of roasts stored in 100% O2, whereas lactic acid bacteria (Lactobacillus and Leuconostoc spp.) predominated on roasts after 1 week in all other atmospheres.

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