Effect of CO₂-N₂ Atmospheres on the Microbial Flora of Pork

Pork loins were vacuum-packaged; one group remained vacuum-packaged, other vacuum packages were injected with gas atmospheres of either 20% CO₂ + 80% N₂ or 40% CO₂ + 60% N₂. Loins were stored for 7, 14, 21 and 28 days at 1-3 C. After each storage interval, chops were prepared from loins and subjected to 5 days of retail display. Psychrotrophic bacterial counts of lean and fat surfaces of loins stored in 40% CO₂ + 60% N₂ were frequently significantly lower than counts of comparable sites of vacuum-packaged loins. Lactobacillus counts of the subcutaneous fat cover of loins stored in CO₂ + N₂ were in most instances (7 of 8 comparisons) significantly higher than those of vacuum-packaged loins; this was true in only 2 of 8 comparisons for the lean surface. Psychrotrophic bacterial counts of chops prepared from loins subjected to the various storage treatments were seldom significantly different. During storage of pork loins, lactobacilli became a predominant part of the microflora and comprised more than 90% of the microflora after 21 days for loins stored in CO₂ + N₂ and after 28 days for vacuum-packaged loins. Pseudomonas spp. continued to persist to a greater degree in the vacuum-packaged loins than in the loins stored in CO₂ + N₂.