The shelf life of a fresh meat product can be measured by a total bacterial enumeration method, which is time-consuming, expensive, and destructive to conduct. Due to these issues, there is interest in developing a shelf life model from an instrument measurement, which has the capability to be less time-consuming, less expensive, and non-destructive. One instrument measurement that could be used to estimate shelf life is dissolved carbon dioxide (CO2). There are few studies published that investigate dissolved CO2 concentrations in the context of shelf life or its relationship to the microbial population. Therefore, the objectives of this study were to determine the dissolved CO2 and O2 concentrations in the purge of vacuum-packaged pork chops during storage, and to determine the relationship between dissolved CO2 and O2 concentrations to the microbial populations and shelf life. Scanning electron microscope (SEM) images were also taken of the packaging film in contact with the meat product to investigate how the biofilm develops on the packaging film throughout the shelf life.

These objectives were completed by taking sixty pork loin chops and placing them into twenty vacuum-packages. In each vacuum-package, a set of purge collection tubes were placed into each bag to collect the purge for the dissolved gas measurements. These packages were stored at 4°C for 60 days, and the packages were sampled randomly on days 0, 5, 15, 30, 45, and 60. On the sample days, the dissolved gases were measured and microbiological analysis conducted.

The results of the experiment demonstrated that the spoilage bacteria increased the dissolved CO2 and decreased the dissolved O2 concentrations during the 60 day storage period by cellular respiration. The lactic acid bacteria (LAB) dominated the spoilage microflora, followed by Enterobacteriaceae and Brochothrix thermosphacta. Since the dissolved CO2 concentrations increased due to the increase in microbial populations, this information was used to develop mathematical models. These mathematical models estimate microbial populations and shelf life based upon dissolved CO2 concentrations in the purge of vacuum-packaged pork chops. The SEM images revealed a two-layer biofilm on the packaging film that was the result of a tri-phase growth environment.