Effect of Packaging under Carbon Dioxide, Nitrogen or Air on the Microbial Flora of Pork Stored at 4°C

Changes in the microbial flora of pork packed in laminated plastic bags and stored at 4 °C were studied in an initial atmosphere of carbon dioxide, nitrogen or air. The time needed for the total aerobic count at 28 °C to reach 5 × 10 6 organisms/cm 2 was about 7 times longer in carbon dioxide than in air, whilst in nitrogen it was about twice as long. The predominant organisms on fresh pork taken directly from the processing line were: Acinetobacter calcoaceticus , non‐fluorescent Pseudomonas spp. and Flavobacterium spp. After storage in air for 7 d, more than 90% of the flora consisted of non‐fluorescent Pseudomonas spp. After storage in nitrogen for 10 d, 70% of the flora consisted of non‐fluorescent Pseudomonas spp. with lower levels of fluorescent Pseudomonas spp., Kurthia zopfii, Aeromonas hydrophila and Lactobacillus plantarum. The non‐fluorescent Pseudomonas spp. could be divided into three different groups, on proteolytic and lipolytic ability; the distribution of the groups was markedly different between pork loins stored in air and nitrogen. On pork stored in carbon dioxide for 21 d the flora consisted of L. plantarum together with lower levels of heterofermentative lactic acid bacteria. When the storage time in carbon doxide was prolonged to 35 d, the proportion of heterofermentative lactic acid bacteria increased to about 50% of the flora.