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Characterizing the role of oxygen in beef discoloration

Denzer, Morgan
The objective of this research was to characterize the role of oxygen in beef discoloration. Limited studies have evaluated the discoloration of the interior of steaks during retail display in association with the development of metmyoglobin. A recent approach in our laboratory has characterized interior color changes by means of needle-probe based single-fiber reflectance (SfR) spectroscopy. The a* values of steaks decreased (P < 0.05) with display time. Metmyoglobin at all depths from 1 mm to 5 mm estimated by the needle-probe SfR increased during display while showing greater metmyoglobin at a depth of 1-mm compared to the depths of 2 – 5 mm. Metmyoglobin estimated at 1 mm depth by the needle-probe SfR and the retail surface by HunterLab spectrophotometer were strongly negatively (P < 0.05) correlated with a* values during retail display. Therefore, internal metmyoglobin formation negatively influences surface color. Furthermore, the display surface was considered as oxygen exposed (OE), while the interior of the steak was denoted as not exposed to oxygen (NOE). NOE steak surface had greater (P < 0.05) metmyoglobin reducing ability compared with OE surfaces on d 6 of display. Oxygen exposure affected the oxygen consumption of the steaks, with the OE surfaces having lower (P < 0.05) oxygen consumption compared to NOE surfaces on d 6 of display. The loss of succinate from d 0 to d 6 of retail display reinforced the decline in color during display. Greater alpha-tocopherol in the NOE surface supported less oxidative changes compared to the OE surface during retail display. These results indicate the presence of oxygen can influence metabolite profile and negatively influence metmyoglobin reducing ability and color. In conclusion, the presence of oxygen can negatively impact the shelf life of steaks; however, the non-exposed interior of muscle remains more biochemically active.