A Case-Ready Modified-Atmosphere Packaging System for Beef.

Beef tenderness and color stability were evaluated in conventional and modified atmosphere packaging (MAP) systems. Equal portions of inside rounds removed immediately (PM0) or at 48 h postmortem (PM48) were vacuum packaged (VP) whole or cut into steaks and packaged in 80%N$\sb2$:20%CO$\sb2$ MAP. On day 12, MAP environments were exchanged for 80%O$\sb2$:20%CO$\sb2$. Calpastatin activity was lower at 2 d postmortem for PM48 steaks than PM0 steaks. Electrophoresis indicated more degradation of 50 and $\u3e$250 kDA compounds at 2 d postmortem for PM48 than PM0 steaks. Steaks from PM48 required less shear force than PM0 steaks. HunterLab \u27L\u27, \u27a\u27 and \u27b\u27 values were higher for PM48 steaks versus PM0 steaks. The lethality of ozone to Escherichia coli (E. coli) and Pseudomonas aeruginosa was investigated using four ozone concentrations (0, 100, 1000, 5000 ppm) and three exposure times (1, 10, 50 min). No differences were detected between 0, 100, or 1000 ppm ozone in log CFU on plates, 5000 ppm resulted lower log CFU. Exposure time had no effect. The experiment was repeated with ozone concentration levels of 0, 1000, 2500, and 5000 ppm. No difference was detected between 0 and 1000 ppm ozone for log CFU per petri dish. Concentrations of either 2500 or 5000 ppm significantly reduced E. coli and Pseudomonas counts. Ground beef (85% lean) was coarsely ground and VP or finely ground (3.2 mm), formed into 113 g patties and packaged in various modified atmospheres (MAP) of 80%O$\sb2$:20%CO$\sb2$ (O$\sb2$); 80%N$\sb2$:20%CO$\sb2$ (N$\sb2$); or 20%CO$\sb2$:2.5%O$\sb2$:77.5%N$\sb2$ ozonated with 2500 ppm ozone (O$\sb3$). After storage at 2$\sp\circ$C for 10 d, ground beef in VP was finely ground and over-wrapped with PVC film on foamed polystyrene trays and O$\sb3$ and N$\sb2$ were exchanged for 80%O$\sb2$:20%N$\sb2.$ No differences were found among N$\sb2$, O$\sb2$, and O$\sb3$ treatments for total plate (TPC), E. coli, and coliform counts. All MAP treatments had lower TPC than VP patties on days 5, 10, 12, and 14. HunterLab \u27a\u27 values and subjective redness scores on day 10 were highest for patties in N$\sb2$ and lowest for O$\sb2$ and O$\sb3.$ Patties in O$\sb2$ exhibited the greatest oxidative instability