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Abstract
This research was conducted to elucidate the mechanism and factors (diet, aging time, antioxidant level, and retail display time) affecting beef toughening in retail display under high oxygen atmosphere packages (HiOx-MAP; 80% O 2 and 20% CO2). In the first study, effects of HiOx-MAP on color and lipid stability of beef m. longissimus lumborum steaks from yearlings fed corn or 30% wet distillers grains plus soluble (WDGS) diets supplemented with (150 mg/kg) or without (0 mg/kg) AGRADO-PLUS (AG) antioxidants were studied. Steak color-shelf life was extended (P < 0.0001) by HiOx-MAP compared to oxygen permeable film packages (PVC-OW). Steaks from corn+AG-supplemented cattle had (P ≤ 0.05) less discoloration and lower lipid oxidation levels at the end of retail display than steaks from all other diets. However, effects of AG on reducing steak discoloration and lipid oxidation when feeding WDGS could not be seen (P > 0.05). In the second study, mechanism and factors affecting beef toughening due to HiOx-MAP during retail display were investigated. High oxygen atmosphere packages oxidized proteins (P < 0.10) and formed protein aggregates (P = 0.01) thereby making steaks tougher (P <.0001). Also, HiOx-MAP reduced (P = 0.001) troponin-T degradation in beef. Protein aggregates were formed mainly by polymerization of myosin proteins mostly due to disulfide bonds. Retail display of steaks aged long-term increased protein oxidation (P <.0001) and polymerization (P < .0007), thereby making beef tougher (P < 0.06). Feeding WDGS also increased protein oxidation (P = 0.002) and polymerization (P < 0.07); however, tenderness was improved ( P = 0.06). Dietary supplementation of AG toughened beef due to protein oxidation (P < 0.04) and decreased (P = 0.001) proteolysis by decreasing (P = 0.007) sarcoplasmic free-calcium levels. In the third study, tenderness and protein oxidation gradient in the beef m. triceps brachii roasts were studied. Protein oxidation, aggregation, and toughening occurred at a descending gradient from the outside to the inside of beef roast packaged in HiOx-MAP systems (P < .0001).
