Department of Animal and Food Sciences, Oklahoma State University, Stillwater, Ok 74078, USA.
Department of Animal Science, Tarleton State University, Stephenville, TX 76402, USA.
J Anim Sci. 2023 Jan 3;101. doi: 10.1093/jas/skac376.
Previous studies investigated the biochemical basis of dark-cutting conditions at elevated muscle pH (above 6), but the molecular basis at slightly above normal pH (between 5.6 and 5.8) is still unclear. The objective was to determine protein and metabolite profiles to elucidate postmortem muscle darkening at slightly elevated pH. Loins were selected based on the criteria established in our laboratory before sample collections, such as pH less than 5.8, L* values (muscle lightness) less than 38, and not discounted by the grader (high-pH beef with dark color are discounted and not sold in retail stores). Six bright red loins (longissimus lumborum) at normal-pH (average pH = 5.57) and six dark-colored strip loins at slightly elevated pH (average pH = 5.70) from A maturity carcasses were obtained within 72-h postmortem from a commercial beef purveyor. Surface color, oxygen consumption, metmyoglobin reducing activity, protein, and metabolite profiles were determined on normal-pH and dark-colored steaks at slightly elevated pH. Enzymes related to glycogen metabolism and glycolytic pathways were more differently abundant than metabolites associated with these pathways. The results indicated that oxygen consumption and metmyoglobin reducing activity were greater (P < 0.05) in darker steaks than normal-pH steaks. Enzymes involved with glycogen catabolic pathways and glycogen storage disease showed lower abundance in dark beef. The tricarboxylic acid metabolite, aconitic acid, was overabundant in darker-colored beef than normal-pH beef, but glucose derivative metabolites were less abundant. The majority of glycogenolytic proteins and metabolites reported as overabundant in the previous dark-cutting studies at high pH (>6.4) also did not show significant differences in the current study. Therefore, our data suggest enzymes involved in glycogen metabolism, in part, create a threshold for muscle darkening than metabolites.
先前的研究调查了肌肉 pH 值升高（高于 6）时暗切条件的生化基础，但 pH 值略高于正常（5.6 至 5.8 之间）时的分子基础仍不清楚。本研究旨在确定蛋白质和代谢物谱，以阐明 pH 值略升高时肌肉死后变黑的原因。根据我们实验室之前在样本收集前建立的标准选择腰部肉，例如 pH 值小于 5.8、L*值（肌肉亮度）小于 38 且不受分级员折扣（高 pH 值的深色牛肉会被折扣，不会在零售店出售）。从商业牛肉供应商处获得的 A 成熟胴体死后 72 小时内，获得 6 块正常 pH 值（平均 pH 值= 5.57）的鲜红腰部肉和 6 块 pH 值略升高的深色带肉。在略升高的 pH 值下，测定正常 pH 值和深色牛排的表面颜色、耗氧量、高铁肌红蛋白还原活性、蛋白质和代谢物谱。与糖酵解途径相关的代谢物的酶与这些途径相关的代谢物相比，具有更高的丰度。结果表明，与正常 pH 值的牛排相比，深色牛排的耗氧量和高铁肌红蛋白还原活性更高（P < 0.05）。参与糖元分解代谢途径和糖原贮积病的酶在深色牛肉中丰度较低。与正常 pH 值牛肉相比，三羧酸代谢物顺乌头酸在深色牛肉中过度丰富，但葡萄糖衍生代谢物含量较低。在先前的高 pH 值（>6.4）暗切研究中报告为过度丰富的大多数糖酵解蛋白和代谢物在本研究中也没有表现出显著差异。因此，我们的数据表明，参与糖元代谢的酶在一定程度上为肌肉变暗创造了一个阈值，而不是代谢物。
