Changes in Microbial Parameters and Gas Composition During Modified Atmosphere Storage of Fresh Pork Loin Cuts

The storage life of modified atmosphere packaged pork loin cuts in 40% CO₂ and 60% N₂ was determined at -1, 4.4, and 10°C in three packaging films with oxygen transmission rates (OTR) of 0.0, 12.6, and 26.5 ml/m²/24 h at 23°C, 0% relative humidity and 1 atm pressure. The pork loin cuts were "commercially" or "aseptically" prepared. Gas atmosphere of the packages, microbial load, and pH were monitored throughout storage. The principal factor influencing change in the headspace gases under the conditions of these studies was gas transmission through the packaging film. A 100-fold difference in initial microbial load between commercially and aseptically prepared meat cuts resulted in a 2-week difference in storage life at both -1 and 4.4°C. Spoilage at each of the three storage temperatures could be attributed to the growth of different groups of bacteria and was influenced by package type. At -1°C, Brochothrix thermosphacta was the predominating microflora of samples stored in plastic film with an OTR of 26.5; lactic acid bacteria predominated on samples stored in foil packs with 0.0 and 12.6 OTR. At 4.4°C, lactic acid bacteria predominated, and at 10°C, Enterobacteriaceae predominated, regardless of packaging film. Under commercial packaging conditions in foil laminate packages with 0.0 or 12.6 OTR, storage life of pork cuts was 5 or 8 weeks at 4.4 or -1°C, respectively. This result was not definitive because of a difference among replicates. Samples in replicate 2 had a reduced storage life at each of the three storage temperatures.