The importance of including metmyoglobin levels in reflectance-based oxygen consumption measurements.

Reflectance-based oxygen consumption measurement utilizes changes in oxymyoglobin levels between bloomed and vacuum-packaged meat, assuming that oxymyoglobin is converted to deoxymyoglobin. However, the interconversion of oxymyoglobin to deoxymyoglobin depends on the age of the meat and the length of display; hence, oxygen consumption calculations might yield inaccurate interpretations if deoxymyoglobin is not the final form. The objective was to evaluate the effectiveness of determining metmyoglobin levels during oxygen consumption analysis and its relationship to beef color stability. Seven psoas major (color labile) and longissimus (color stable) were displayed in retail for 6 d and evaluated for oxygen consumption on the retail (oxygen exposed) and interior (non­oxygen exposed) surfaces. The retail surface had greater (P < 0.05) metmyoglobin formed during oxygen consumption than the interior surface on d 6 of the display. Furthermore, the psoas major muscle exhibited greater (P < 0.05) metmyoglobin content during oxygen consumption than the longissimus on the retail surface paralleling with the decline in color stability. Therefore, the study indicates that sampling location and including metmyoglobin content in oxygen consumption calculations, along with changes in oxymyoglobin, will better explain meat color stability.

Novel needle-probe single-fiber reflectance spectroscopy to quantify sub-surface myoglobin forms in beef psoas major steaks during retail display.

Meat discoloration starts at the interface between the bright red oxymyoglobin layer and the interior deoxymyoglobin layer. Currently, limited tools are available to characterize myoglobin forms formed within the sub-surface of meat. The objective was to demonstrate a needle-probe based single-fiber reflectance (SfR) spectroscopy approach for characterizing sub-surface myoglobin forms of beef psoas major muscles during retail storage. A 400-µm fiber was placed in a 17-gauge needle, and the assembly was inserted into the muscle at five depths of 1 mm increment and 1 cm lateral shift. Metmyoglobin content increased at all depths during display and content at 1 mm was greater compared to that of 2 to 5 mm depth. The a* values decreased (P < 0.05) during retail display aligning with the sub-surface formation of metmyoglobin. In summary, the results suggest that needle-probe SfR spectroscopy can determine interior myoglobin forms and characterize meat discoloration.

Metabolomics and bioinformatic analyses to determine the effects of oxygen exposure within longissimus lumborum steak on beef discoloration.

Meat discoloration starts from the interior and spreads to oxymyoglobin layer on the surface. The effects of oxygen exposure within a steak on the metabolome have not been evaluated. Therefore, the objective of this study was to evaluate the impact of oxygen exposure on the metabolome of the longissimus lumborum muscle. Six United States Department of Agriculture (USDA) Low Choice beef strip loins were sliced into steaks (1.91-cm) and packaged in polyvinyl chloride overwrap trays for 3 or 6 d of retail display. The oxygen exposed (OE) surface was the display surface during retail, and the non-oxygen exposed (NOE) surface was the intact interior muscle. The instrumental color was evaluated using a HunterLab MiniScan spectrophotometer. To analyze the NOE surface on days 3 and 6, steaks were sliced parallel to the OE surface to expose the NOE surface. Metmyoglobin reducing ability (MRA) was determined by nitrite-induced metmyoglobin reduction. A gas chromatography-mass spectrometry was used to identify metabolites. The a* values of steaks decreased (P < 0.05) with display time. MRA was greater (P < 0.05) in the NOE surface compared with the OE surface on days 3 and 6. The KEGG pathway analysis indicated the tricarboxylic acid (TCA) cycle, pentose and glucuronate interconversions, phenylalanine, tyrosine, and tryptophan metabolism were influenced by the oxygen exposure. The decrease in abundance of succinate from days 0 to 6 during retail display aligned with a decline in redness during display. Furthermore, citric acid and gluconic acid were indicated as important metabolites affected by oxygen exposure and retail display based on the variable importance in the projection in the PLS-DA plot. Citric acid was lower in the NOE surface than the OE surface on day 6 of retail display, which could relate to the formation of succinate for extended oxidative stability. Greater alpha-tocopherol (P < 0.05) 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 promote migration of the metmyoglobin layer from interior to surface.

In a retail setting, aerobic packaging allows beef steaks to form a bright-cherry red appearance. However, prolonged oxygen exposure can also lead to surface discoloration, which is negatively perceived by consumers. Surface discoloration results in either discounts or products being discarded in the grocery store resulting in approximately $3.7 billion loss annually in the United States. Hence, understanding the process of oxygen exposed discoloration would help to limit the economic loss and meat waste. The current study evaluated the impact of oxygen exposure on metabolites, oxygen consumption, and metmyoglobin reducing activity of beef strip loin steaks. The results indicated that oxygen exposure decreased metmyoglobin reducing activity. Furthermore, metabolites that could limit surface discoloration showed lower abundance in oxygen-exposed surface during retail display. Oxygen negatively impacts the color of beef loin steaks and the stability of the color during retail. Expanding our knowledge of processes involved in metmyoglobin formation could help to develop strategies to help limit economic loss associated with surface discoloration.

Sarcoplasmic model to study the effects of high-pressure processing on beef color.

High-pressure processing (HPP) negatively impacts fresh meat color. The objective of the study was to use a sarcoplasmic (meat extract) model to better understand the effects of HPP on meat color. Sarcoplasm was extracted at pHs of 5.6, 6.0, or 6.4 and fractioned based on centrifugation speed at 0, 3500 g, and 15,000 g for 5 min. The extracts were processed using a commercial HPP unit at 300 MPa, 450 MPa, and 600 MPa, along with a non-pressurized control. Myoglobin concentration decreased (P < 0.05) with increased HPP levels. Sarcoplasm treated with 300 MPa had the greatest oxymyoglobin content (P < 0.05) compared with the non-pressurized control and other HPP levels. Deoxymyoglobin and metmyoglobin content were greater at 600 MPa compared with non-pressurized control and other HPP levels. In summary, higher pH and lower pressure can improve redness of sarcoplasm.