宰前急性热应激诱导类PSE鸡肉形成的分子机制

The PSE-like (pale, soft and exudative) chicken meat has a poor quality, and is not suitable for further processing. The high occurrence has been a growing problem needed to be urgently addressed for broiler industry. Acute heat stress before slaughter is one of the most important factors that cause the PSE-like chicken meat in summer. However, the underlying molecular mechanism is poorly defined. The objective of this study is to ascertain the molecular mechanisms by the research on the changes of protein expression and carbohydrate metabolism in chicken breast muscle in PSE-like meat induced by acute heat stress, through biological technologies such as isobaric tag for relative and absolute quantification (iTRAQ), LC-MS/MS and Western blotting. Carbohydrate metabolism changes will be revealed by the research on glycolytic potential, activity of key enzymes and AMPK, combined with the information of differential expression proteins related to carbohydrate metabolism. The relationship between AMPK and glycolysis, and the effect of glycolysis on meat quality will be determined. The changes of protein expression will be revealed through the proteomics analysis. The key differential expression proteins related to PSE-like chicken meat will be determined through correlation analysis. The relationships between the key differential expression proteins with quality of PSE-like chicken meat, and with the glycolysis changes will be analyzed. The findings will provide new information for PSE-like chicken meat forming mechanism and provide a new theoretical basis for the pre-slaughter managements for poultry.

类PSE鸡肉品质差，加工性能低，不适于现代肉鸡加工业，其高发生率已成为鸡肉加工业迫切需要解决的问题。宰前急性热应激是导致该类肉产生的主要宰前因素，但其影响的相关分子机制还未阐明。本项目拟借助同位素相对标记和绝对定量技术（iTRAQ）、液相串联质谱分析技术（LC-MS/MS）和Western blotting等技术，从宰后蛋白表达变化和糖代谢变化两方面探讨宰前急性热应激诱导类PSE鸡肉形成的分子机制。通过对糖酵解潜能、糖酵解关键酶活性和AMPK等的研究，结合与糖代谢有关的关键差异蛋白信息，阐明宰后糖酵解变化与类PSE鸡肉形成的关系。通过对类PSE肉蛋白组的研究，分析急性热应激诱导的类PSE鸡肉蛋白表达变化，筛选出与类PSE肉相关的关键差异表达蛋白，分析其与糖代谢变化和类PSE鸡肉肉质的关系。该研究可为发展和完善类PSE鸡肉的形成机制提供新的理论依据，为肉鸡宰前热应激的控制提供科学依据。

本研究针对该问题开展了夏季类PSE鸡肉判定标准的建立和其品质特征研究、宰前急性热应激和屠宰工艺对鸡肉品质及宰后糖代谢影响的研究、不同热应激程度对鸡肉品质、AMPK活性、糖代谢规律和肌肉微观结构影响的研究和宰前急性热应激对鸡胸肉蛋白组学影响的研究。研究发现，宰前36℃热应激更容易形成类PSE鸡肉，而高温热应激（>38℃）发生的概率可能会降低，但容易引起更高的死亡率；肉鸡宰后的热烫冷却工艺不能消除热应激造成的负面影响；热应激效应可能在短时间内就会形成（<1h）。通过糖酵解进程分析、AMPK活性分析、肌肉超微结构变化分析和差异蛋白组学分析明确了宰前热应激诱导类PSE形成的分子机制。宰前36℃ ~ 38℃热应激可能使肌肉在宰后能量代谢迅速降低，激活了AMPK活性，并进一步提高了糖酵解进程中关键酶丙酮酸激酶PK、6-磷酸果糖激酶PFK和糖原磷酸化酶的活性，促进了宰后早期糖酵解进程，使pH值在胴体温度较高的时候过快下降，导致蛋白变性，最终形成了类PSE鸡肉。但是40℃热应激条件下，AMPK活性和糖酵解进程中的关键酶活性未得到提高，因而，糖酵解进程并未加快，因而类PSE鸡肉发生率较36℃降低。其次，不同热应激程度下肌肉微观结构的变化也是鸡肉品质发生变化的一个内部原因。36℃热应激加快了肌原纤维的降解，肌原纤维小片化现象明显；而40℃热应激条件下，肌原纤维间距增大现象突出，肌原纤维小片化现象不明显。这可能降低了光的反射，增加了水分存在的内部空间，表观为亮度降低，保水性升高。.本研究发现了宰前急性热应激影响鸡肉品质的规律，阐明了其诱导类PSE鸡肉形成的分子机制，对肉鸡的宰前管理提供了数据和理论指导。基于此结果，严格控制肉鸡宰前运输温度是控制类PSE鸡肉发生率的最佳手段，建议最好在36℃以下。