Characterizing the Biochemical Attributes of Oxygen- and Non–Oxygen-Exposed Surfaces to Understand the Features That Influence Color Stability of Beef Longissimus Lumborum Steaks

Limited knowledge is currently available on how different biochemical parameters accurately predict variability in beef color stability. The objectives were to evaluate the contributions of lipid oxidation, metmyoglobin-reducing activity, oxygen penetration, and oxygen consumption of oxygen-exposed and non–oxygen-exposed surfaces to predict color stability of the longissimus lumborum muscle. Steaks were sliced (1.91 cm) from USDA Low Choice beef strip loins (n = 7), packaged in polyvinyl chloride overwrap trays, and randomly assigned to 3 or 6 d of retail display. During display, instrumental color was evaluated daily using a HunterLab MiniScan spectrophotometer. The display surface was considered as oxygen exposed, whereas the interior of the steak was denoted as non–oxygen-exposed. The non–oxygen-exposed surface was obtained by slicing the steak in half parallel to the surface previously exposed to oxygen. The non–oxygen-exposed and oxygen-exposed surfaces were used to determine oxygen consumption, metmyoglobin-reducing activity, and lipid oxidation. Nitrite-induced metmyoglobin reduction was used to measure metmyoglobin-reducing activity, whereas oxygen con- sumption was calculated using 2 different approaches (as changes in oxymyoglobin with incubation and metmyoglobin formation during oxygen consumption). With increased display time, a* values (redness) decreased (P < 0.05) for instru- mental color. The non–oxygen-exposed steak surface had greater (P < 0.05) metmyoglobin-reducing activity compared with oxygen-exposed surfaces. Oxygen exposure affected the oxygen consumption of the steaks, with the oxygen-exposed surfaces having lower (P < 0.05) oxygen consumption compared to non–oxygen-exposed surfaces on day 6 of display. The exposure of oxygen to the muscle resulted in a decrease in activity, paralleling in decline in retail color and color stability. Oxygen-exposed surface metmyoglobin-reducing activity was strongly correlated (r = 0.77; P < 0.05) with a* values. Metmyoglobin levels during oxygen consumption had a strong relationship (R2 = 0.47; P < 0.05) with a* values. The presence of oxygen can result in negative impacts on the shelf life of steaks; however, the non-exposed interior of the muscle remains more biochemically active. Based on the feature selection using lasso regression, oxygen penetration, metmyoglobin levels during oxygen consumption, and initial metmyoglobin levels during metmyoglobin-reducing activity can predict beef longissimus lumborum color stability.