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G. TEWARI¹, D. S. Jayas¹, L. E. Jeremiah², and R. A. Holley³. (1) Biosystems Engineering, University of Manitoba, Winnipeg, MB R3T 5V6, Canada, (2) Meat Research, Agriculture and Agri-Food Canada, Lacombe, AB T4L 1B2, Canada, (3) Food Science, University of Manitoba, Winnipeg, MB R3T 2N2, Canada

Centrally prepared retail beef cuts stored in controlled atmospheres containing nearly 100% CO₂ or N₂ may contain small amounts of O₂, making them susceptible to the formation of metmyoglobin as a result of the presence of the residual O₂. Such discoloration is highly undesirable when commercial conditions require periodic rapid distribution and display of centrally packaged meat.

The present work was conducted to assess the capability of commercial O₂ scavengers to prevent transient discoloration of centrally prepared retail-ready beef steaks.

Beef steaks placed on retail trays with or without O₂ scavengers, over-wrapped with high-O₂-permeable film, were placed into master packs. Each master pack contained four such retail trays in a controlled atmosphere of 100% N₂. The master packs were stored at 1 ± 0.5°C. Three master packs, one containing control and the other two containing two types of commercial scavengers, were opened daily for eight days. The steaks were evaluated for visual characteristics using a trained panel and for metmyoglobin content by reflectance spectrophotometer.

After most storage intervals, steaks packaged without O₂ scavengers received higher discoloration scores (3: 11-25% discoloration, or 4: 26- 50% discoloration), lower retail appearance scores (3: slightly undesirable), and higher metmyoglobin content (>20%) compared to steaks with O₂ scavengers (p<0.05). Steaks packaged with O₂ scavengers had low discoloration scores (1: 0% discoloration), high retail appearance scores (6: desirable, or 7: extremely desirable), and low metmyoglobin content (<5%), for all retail display periods. Although O₂ scavengers were effective in reducing metmyoglobin formation, the prevention of metmyoglobin formation was not significantly influenced by the type of O₂ scavenger employed (p>0.05).

The O₂ scavengers have the potential to prevent transient discoloration of centrally prepared beef cuts, but factors such as selection of packaging systems, O₂ scavenger formulation, and package atmospheres (N₂/CO₂) may affect results.