| Summary: | The aim of this study was to investigate the effects of different packaging systems on the shelf life of refrigerated ground beef. The ground beef samples were packaged as follows: AA (100% ambient air), 90O<sub>2</sub>:10CO<sub>2</sub> (90% O<sub>2</sub> and 10% CO<sub>2</sub>), 80O<sub>2</sub>:20CO<sub>2</sub> (80% O<sub>2</sub> and 20% CO<sub>2</sub>), 70O<sub>2</sub>:30CO<sub>2</sub> (70% O<sub>2</sub> and 30% CO<sub>2</sub>), 60O<sub>2</sub>:40CO<sub>2</sub> (60% O<sub>2</sub> and 40% CO<sub>2</sub>), 50O<sub>2</sub>:50CO<sub>2</sub> (50% O<sub>2</sub> and 50% CO<sub>2</sub>), 100O<sub>2</sub> (100% O<sub>2</sub>), and VP (vacuum packaging). All treatments were analyzed daily for O<sub>2</sub> and CO<sub>2</sub> levels, pH, filtration time, total volatile basic nitrogen (TVB-N), aerobic mesophilic heterotrophic bacteria (AMHB), and aerobic psychrotrophic heterotrophic bacteria (APHB) over 20 days at 2 °C. All MAP systems had a decrease of O<sub>2</sub> and an increase of CO<sub>2</sub> levels during storage period (<i>p</i> < 0.05). Overall, the MAP systems were similarly able to decrease the pH and retard the increase of TVB-N and filtration time over the storage period (<i>p</i> > 0.05). Moreover, the MAP systems increased the lag phase and/or the generation time of both AMHB and APHB, extending the shelf life by 3 (90O<sub>2</sub>:10CO<sub>2</sub>), 4 (70O<sub>2</sub>:30CO<sub>2</sub> and 100O<sub>2</sub>), and 5 days (80O<sub>2</sub>:20CO<sub>2</sub>, 60O<sub>2</sub>:40CO<sub>2</sub>, 50O<sub>2</sub>:50CO<sub>2,</sub> and VP). All MAP systems were equally effective in retarding physicochemical degradation; however, 80O<sub>2</sub>:20CO<sub>2</sub>, 60O<sub>2</sub>:40CO<sub>2</sub>, 50O<sub>2</sub>:50CO<sub>2,</sub> and VP were the most effective in impairing bacterial growth and extending the shelf life of ground beef stored under refrigeration.
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