The oxygen (O2) absorption kinetics of six commercial O2 scavengers were studied. The scavengers were placed in bags which were filled with 240 mL of air, 4.5 L N2 + 15 mL of air, or 3.5 L CO2 + 9 mL of air. The O2 concentration in each bag was measured at hourly intervals for 8 h. The effects of variability among individual scavengers, initial O2 concentrations of 20% or 500 ppm (0.05%), temperatures of 25, 12, 2 or −1.5 °C, and scavenger capacity on the O2 absorption rate were determined. In addition, the effect of placing scavengers within over‐wrapped trays within bags, was examined. Rates of O2 absorption varied by factors of up to 2 between individual O2 scavengers of the same type, but rates of absorption by groups of four scavengers of the same type were similar. Low temperatures gave longer O2 half‐life when compared with those at higher temperatures, e.g. O2 half‐lives of 7.1 and 1.0 h at −1.5 and 25 °C, respectively, were obtained for one scavenger type. Shorter O2 half‐lives were obtained in air than in N2 atmospheres at the same temperature, e.g. O2 half‐lives of 1.0 and 3.3 h in air and N2 at 25 °C, respectively, were obtained for one scavenger type. The O2 absorption reactions were of first order for both high and low initial O2 concentrations. However, O2 concentration was the primary limiting factor for O2 absorption in atmospheres having O2 concentration of 500 ppm because of the dominance of diffusion. Scavengers, when placed within over‐wrapped trays within bags had up to 12 times longer O2 half‐lives, indicating that the O2 permeable film acts as an O2 barrier when pack atmosphere has low O2 concentrations. To obtain consistent and reproducible results, it is recommended that multiple scavengers be used in a packaging system. The appropriate number should be based on scavenger type, desired O2 absorption rate, storage temperature, and pack atmosphere (air/N2/CO2).

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Centralized packaging of retail meat cuts is growing more popular because of its economies and potential to maintain quality, enhance safety, and extend the shelf life of fresh meat. Requirements for optimizing shelf life of centrally prepared retail cuts for periods up to 15 weeks are slightly different from those needed to extend the shelf life of fresh, chilled meat. Chilled meat primarily deteriorate at the cut or uncut muscle surface. In long-term storage, primal cuts are placed in an atmosphere saturated with carbon dioxide and containing very low residual oxygen. These cuts are held at -1.5+/-0.5 degrees C. When the meat is removed, it is fabricated into retail or food service cuts. New fresh surfaces are created in the process, revitalizing the meat's appearance. After being prepared for retail display, the meat normally has four more days of shelf life. Depending on the meat species, shelf life is usually limited by development of undesirable organoleptic changes, usually defects in color, which are independent of microbial presence. The microbes consist of a lactic acid bacterial population that maximizes under storage conditions at about 10(8) CFU/cm2 well before shelf life ends. Circumstances are different with centralized distribution of retail-ready fresh meat. The wholesale storage period following initial packaging of the retail cuts is about 20 to 30 days. Prepared products must withstand retail display for up to 2 days without further manipulation of package contents. Retail packages are simply moved from their storage container (usually a unit or overwrap containing a modified atmosphere) to retail display, where desirable meat color develops upon exposure to air. Three gas atmospheres have some potential to satisfy storage needs for centralized distribution of retail-ready packages: 100% CO2, 100% N2, or 70% N2 + 30% CO2. Shelf life is limited by undesirable changes in surfaces exposed at initial packaging, caused by growth of psychrotrophic bacteria. If 100% CO2 is used, these are all lactic acid bacteria (LAB). Therefore, initial bacterial numbers on the meat and storage temperature become critical to success. The most attractive storage option is 100% CO2 used at - 1.5 +/-0.5 degrees C. This review presents the reason for that recommendation, along with basic concepts of meat chemistry, a discussion of modified atmosphere packaging, meat microbiology, and current results with simulated centralized packaging of retail-ready meats.

Oxygen absorbent technology in conjunction with controlled atmosphere packaging(CAP) was used to prevent transient discoloration in master-packaged beef steaks. Two types of commercial O 2 scavengers were used in the study. The master packs were stored at 1Ϯ 0.5 ЊC. The steaks from master packs were presented in a display-case for visual evaluation. Reflectance spectra from each steak-surface were obtained to estimate metmyoglobin content. Steaks packaged without O 2 scavengers showed more discoloration, and had significantly higher proportions of metmyoglobin when compared to steaks with O 2 scavengers, after most storage intervals (p Ͻ 0.05). Prevention of metmyoglobin formation was influenced by the number but not the type of O 2 scavenger employed (p Ͼ 0.05).