Instituto de Ciencia Animal, Facultad de Ciencias Veterinarias, Universidad Austral de Chile, Valdivia, Chile.
Instituto de Bioquímica y Microbiología, Facultad de Ciencias, Universidad Austral de Chile, Valdivia, Chile.
PLoS One. 2021 Jan 28;16(1):e0229480. doi: 10.1371/journal.pone.0229480. eCollection 2021.
Postmortem muscle temperature affects the rate of pH decline in a linear manner from 37.5°C to 0-2°C. The pH decline is correlated with the enzymatic degradation of glycogen to lactate and this process includes the metabolic coupling between glycogenolysis and glycolysis, and that are strongly upregulated by the AMPK. In this study, we used 12 samples previously characterized by have different muscle glycogen concentration, lactate and AMPK activity, selected from 38 steers that produced high final pH (>5.9) and normal final pH (<5.8) carcasses at 24 h postmortem. Moreover, we evaluated changes in the AMPK activity in samples from both categories incubated at 37, 25, 17 and 5°C and supplemented with exogenous glycogen. Finally, we analysed if there were structural differences between polymers from both categories. Our results showed that "in vitro" enzymatic AMPK activity evaluated at both 0.5 or 24 h was greater in samples from normal then high pH categories (p <0.01), and in all temperature of incubation analysed (17, 25 and 37°C). For other hand, a greater AMPK activity were obtained in samples incubated at 17 that 25 or 37°C, in normal carcasses at both 0.5 or 24 h (p < 0.01), as also in samples from carcasses categorized as high pH, but at 24 h (p < 0.05). Interestingly, AMPK activity was totally abolished at 5°C, independent of final pH category of carcasses, and was confirmed that the incubation temperature at which the maximum activity was obtained (p < 0.01), at least in carcasses with a normal pH is at 17°C. The enzymatic AMPK activity did not change in relation to excess glycogen (p > 0.05) and we did not detect structural differences in the polymers present in samples from both categories (p > 0.05), suggesting that postmortem AMPK activity may be highly sensitive to temperature and not to in vitro changes in glycogen concentration (p > 0.05). Our results allow concluding that normal concentrations of muscle glycogen immediately at the time of slaughter (0.5 h) and an adequate cooling managing of carcasses are relevant to let an efficient glycogenolytic/glycolytic flow required for lactate accumulation and pH decline, through the postmortem AMPK signalling pathway.
死后肌肉温度以线性方式从 37.5°C 降低到 0-2°C，影响 pH 值下降速度。pH 值下降与糖原分解为乳酸的酶促降解相关，该过程包括糖原分解和糖酵解之间的代谢偶联，而 AMPK 强烈上调了这种偶联。在这项研究中，我们使用了 12 个样本，这些样本之前的特征是肌肉糖原浓度、乳酸和 AMPK 活性不同，是从 38 头在死后 24 小时产生高最终 pH 值（>5.9）和正常最终 pH 值（<5.8）胴体的牛中选择的。此外，我们评估了在 37°C、25°C、17°C 和 5°C 下孵育并补充外源性糖原的这两个类别样本中 AMPK 活性的变化。最后，我们分析了这两个类别聚合物之间是否存在结构差异。我们的结果表明，在 0.5 小时或 24 小时评估的“体外”酶 AMPK 活性在正常 pH 值类别中大于高 pH 值类别（p<0.01），并且在所有分析的孵育温度（17°C、25°C 和 37°C）下都是如此。另一方面，在正常胴体中，在 17°C 下孵育的样本在 0.5 小时或 24 小时时获得的 AMPK 活性更大（p<0.01），而在高 pH 值类别中也是如此，但在 24 小时时（p<0.05）。有趣的是，AMPK 活性在 5°C 时完全被抑制，与胴体的最终 pH 值类别无关，并证实了获得最大活性的孵育温度（p<0.01），至少在 pH 值正常的胴体中为 17°C。在过量糖原存在的情况下，酶 AMPK 活性没有变化（p>0.05），我们没有检测到两个类别样本中聚合物的结构差异（p>0.05），这表明死后 AMPK 活性可能对温度非常敏感，而不是对体外糖原浓度的变化敏感（p>0.05）。我们的结果表明，屠宰时肌肉糖原的正常浓度（0.5 小时）和胴体的适当冷却管理对于通过死后 AMPK 信号通路积累乳酸和降低 pH 值所需的有效糖原分解/糖酵解流是至关重要的。
