Microbiology of Pork Packaged in Various Gas Atmospheres

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.