Effect of modified atmosphere packaging on shelf life of beef loin steaks

The effect of modified atmosphere packaging and gas volume on shelf life of beef steaks was studied. Boneless loin steaks (2.54 cm thick) were packaged with PVC film (control), vacuum packaged or vacuum packaged followed by injection of a gas mixture of either 1) 80%O₂ : 20%CO₂, 2) 40%O₂ : 15%CO₂ : 45%N₂, 3) 5%O₂ : 20%CO₂ : 75%N₂ and/or 4) 0%O₂ : 25%CO₂ : 75%N₂. The gases were injected at three different volumes: 500, 1000 or 1500 ml. Steaks were then displayed at 3°C for 1, 4, 9, 12, 16, 19 or 22 days. At the end of each display period gas composition inside the packages, objective and subjective surface color, pH and microbial counts were determined.

Gas volume had no effect on shelf life characteristics. In general, consumer panelists preferred steaks that were packaged in the atmospheres containing 80% and 40% oxygen. After day 4, panelists reported steaks for all treatments (except vacuum packaged steaks) were unacceptable due to discoloration. As display days increased acceptability of vacuum packaged increased. Oxymyoglobin and myoglobin percentages decreased and metmyoglobin percent increased as display days increased. Steaks displayed through day 4 had a greater (P<.05) oxymyoglobin and myoglobin percentage than steaks displayed past day 4. Through day 4, the Hunter colorimeter measured a brighter, redder color than after day 4, also, the steaks packaged in 80%O₂ : 20%CO₂ had a greater Hunter "b" value than steaks packaged in 0%O₂ : 25%CO₂ : 75%N₂ and vacuum packaged steaks. The volume of gas had no effect on coliforms, lactic acid producing bacteria, aerobic plate count and psychrotrophic bacteria. There was an increase (P<.05) in aerobic, psychrotrophic and lactic acid bacterial plate counts as display time increased for the steaks packaged in 0%O₂ : 25%CO₂ : 75%N₂. There were no significant differences in bacteria growth over display days for the other treatments.