宰后肌肉能量代谢对肉品质的影响研究进展

肉色、嫩度、保水性等肉的品质特性一直是影响消费者购买意愿的重要因素,而肌肉能量代谢会影响肌肉的生长、发育、成熟过程,并最终影响肉的食用品质。磷酸肌酸系统、糖酵解途径和氧化磷酸化是肌肉中ATP主要来源,并在宰后不同时期发挥主要作用。动物屠宰放血后,肌肉内环境发生变化,不同的供能方式会影响能量代谢过程,从而影响肌肉转化为“肉”的过程。本文综述宰后肌肉能量代谢过程及其对肉品质的影响,并阐述腺苷酸活化蛋白激酶（AMP-activated protein kinase,AMPK）和沉默信息调节因子（silent information regulators,SIRTs）家族对代谢过程的影响,以期为通过能量代谢过程调控肉品质的形成提供新的思路。     

Mechanisms controlling pork quality development: The biochemistry controlling postmortem energy metabolism

Pale, soft and exudative (PSE) pork represents considerable economic losses for the industry due to its limited functionality and undesirable appearance. During the past several decades, exhaustive research covering various aspects of the food chain has established genotyping procedures, recommended handling practices, and quality indicators in order to reduce the incidence of inferior pork quality. Despite these efforts, there is still a relatively high occurrence of PSE pork. Development of pork quality attributes is largely governed by the rate and extent of postmortem pH decline. The combination of high temperature at low pH or abnormally low ultimate pH causes denaturation of sarcoplasmic and myofibrillar proteins, resulting in paler color and reduced water holding capacity. The pH decline is closely related to muscle energy availability and demand at or around slaughter. The postmortem degradation of glycogen through glycogenolysis and glycolysis provides ATP to help meet energy demand and decreases pH by generating lactate and H+. Therefore, the flux of metabolites through glycolysis, the involvement of energy signaling pathways that modulate glycolytic activity, and the inherent metabolism of different fiber types are critical factors influencing pH decline and pork quality. Further, recent work implicates adenosine monophosphate-activated protein kinase (AMPK) as a major energy sensor for the cell, and thus may be involved in the control of postmortem metabolism. The intent of this paper is to review the biochemistry controlling postmortem energy metabolism in pig muscle and explore new information generated using genetic mutations in order to define the fundamental mechanisms controlling the transformation of muscle to meat.     

Stress Effects on Meat Quality: A Mechanistic Perspective

Stress inevitably occurs from the farm to abattoir in modern livestock husbandry. The effects of stress on the behavioral and physiological status and ultimate meat quality have been well documented. However, reports on the mechanism of stress effects on physiological and biochemical changes and their consequent effects on meat quality attributes have been somewhat disjointed and limited. Furthermore, the causes of variability in meat quality traits among different animal species, muscle fibers within an animal, and even positions within a piece of meat in response to stress are still not entirely clear. This review 1st summarizes the primary stress factors, including heat stress, preslaughter handling stress, oxidative stress, and other stress factors affecting animal welfare; carcass quality; and eating quality. This review further delineates potential stress‐induced pathways or mediators, including AMP‐activated protein kinase‐mediated energy metabolism, crosstalk among calcium signaling pathways and reactive oxygen species, protein modification, apoptosis, calpain and cathepsin proteolytic systems, and heat shock proteins that exert effects that cause biochemical changes during the early postmortem period and affect the subsequent meat quality. To obtain meat of high quality, further studies are needed to unravel the intricate mechanisms involving the aforementioned signaling pathways or mediators and their crosstalk.     

Effects of nitric oxide and oxidation in vivo and postmortem on meat tenderness

Metabolic processes in muscle tissue in vivo result in the production of reactive oxygen species and oxidative compounds including superoxide anions and nitric oxide (NO). Reactive oxygen species can react with both lipids and proteins and often have deleterious effects, contributing to the onset of ageing and senescence as well as cell death. Nitric oxide (NO) is a free radical that is constantly produced or released throughout the body by diverse tissues and is known to influence proteolytic activity in human and rodent skeletal muscle as well as being involved in regulation of calcium homeostasis in the muscle cell. The influence of nitric oxide on development of meat tenderness has been studied through postmortem manipulation and also through in vivo studies. The effect of NO on meat tenderness is postulated to be via its regulatory effects on the proteins calpain, cathepsins, ryanodine receptor channel in the sarcoplasmic reticulum (SR) and the sarcoplasmic-endoplasmic release calcium ATPase in the SR. NO is an oxidant although the effects of NO on effector proteins can be distinguished from a direct oxidation reaction. The onset of oxidation in meat postmortem is well known to produce off-odours, discolouration and unacceptable flavours associated with rancidity. Oxidation during the immediate postmortem period appears to inhibit tenderisation during ageing, probably through an inhibitory effect of oxidation on the calpain enzyme. Oxidation of muscle tissue occurring as a result of availability of oxygen during modified atmosphere packaging may also have deleterious consequences for tenderness development during storage of meat prior to retail display. In conclusion, it is proposed that postmortem meat tenderisation is influenced by skeletal muscle's release of NO pre-slaughter and the oxidation of proteases postmortem. This proposal is compatible with the existing tenderness model and will hopefully assist in increasing the accuracy of prediction of meat tenderness. Future directions for research are discussed.     

蛋白质乙酰化对宰后肉品质调控的研究进展

蛋白质乙酰化是一种动态、可逆的蛋白质翻译后修饰方式,它是连接乙酰辅酶A代谢与机体细胞信号转导重要的蛋白质翻译后修饰类型,可以调节基因表达、代谢、细胞凋亡、钙信号传导、蛋白质水解、肌肉收缩以及疾病预防.宰后肌肉的糖酵解、肌肉收缩以及细胞凋亡对肉品质的形成具有重要影响,因此,蛋白质乙酰化可能通过调节宰后肌肉的糖酵解、肌肉收...     

宰后成熟对生鲜肉品质影响的研究进展

作为一种肉品增值手段,成熟技术多年来在全球肉类工业中已被广泛应用。在宰后初期肌肉转化为可食用肉及后期成熟过程中所发生的一系列生化变化都会对肉的品质产生重要影响。因此,通过优化成熟方案并引入新型成熟技术来有效提升肉品品质（特别是嫩度）尤为重要。近年来,对肉品宰后生理生化机制的探索和新型成熟技术的研究始终是该领域的热点,然而目前鲜见对该方面最新进展的综合性报道。因此,本文系统地总结了对肉品质起决定性作用的宰后早期生理生化变化,概述了现行不同成熟方法（干法成熟和湿法成熟）对肉品质的影响,并对新型成熟技术的发展及其对品质的改善效果进行了综述,以期为满足消费者日益增长的高品质肉品消费需求和促进我国肉品加工行业的发展提供理论技术指导和发展思路。     

氧化应激降低鸡肉品质的作用机制研究进展

氧化应激会引发肉鸡的恐惧和躁动,造成生理代谢失调,这不仅会降低肉鸡肌肉pH值,增加滴水损失,导致鸡肉品质变差,而且还会降低加工特性。鸡肉品质下降的主要原因为：肌肉中的能量代谢平衡被打破,导致有氧呼吸减弱,无氧酵解增强,引起肌肉中乳酸的大量积累,导致肌肉pH值快速下降;钙离子代谢紊乱,引发肌细胞膜破损;线粒体结构和功能受损,导致线粒体外膜透化,促进凋亡因子释放至细胞质,激活内源性细胞凋亡途径。文章从肉鸡的能量代谢、钙离子代谢和细胞凋亡三个方面,本文深入介绍了氧化损伤的发生机制,在生产实践中寻求缓解肉鸡氧化应激的方法以提高鸡肉品质,促进肉鸡产业健康发展提供理论基础。     

Lessons to learn about postmortem metabolism using the AMPKγ3(R200Q) mutation in the pig

The development of pork quality attributes - including color, water holding capacity, and texture - are controlled largely by the rate and extent of postmortem pH decline. In turn, pH decline is thought to follow the anaerobic degradation of glycogen to "lactic acid". The "Hampshire effect" or Rendement Napole (RN(-)) pig, which has elevated muscle glycogen, propagated the widespread use of "glycolytic potential" to describe muscle's capacity for postmortem glycolysis. Since the evolution of glycolytic potential, there have been great strides in molecular and technical capabilities. Hence, it must be appreciated that the RN(-) pig possesses a mutation in the gene encoding the AMP-activated protein kinase (AMPK) γ3 subunit, which results in a non-conservative amino acid substitution (R200Q). AMPK, a major energy sensor in skeletal muscle, influences enzyme activity, gene and protein expression, fiber type, and mitochondrial biogenesis. The utility of glycolytic potential as indicator of ultimate pH should be reevaluated in the context of the metabolic differences between AMPKγ3 mutated and normal muscle. Understanding the metabolism and energetics in AMPKγ3 mutated muscle may provide insight into the mechanisms influencing the rate and extent of postmortem metabolism.     

BIOPHYSICAL BASIS OF PALE, SOFT, EXUDATIVE (PSE) PORK AND POULTRY MUSCLE: A REVIEW

Problems with meat quality are usually caused by aberrations in the biochemistry and morphology of individual muscles, as well as by postmortem events. Poultry, like pigs, have been subjected to intense genetic selection for rapid lean muscle growth. The selection traits are most often associated with economic importance rather than biophysical significance, which often results in stress syndromes (e.g. porcine stress syndrome) and pale, soft, exudative (PSE) muscle conditions. The occurrence of PSE muscle and subsequent alterations in meat quality has been shown to be related to increases in muscle size, stressful preslaughter handling conditions, and rate of onset of rigor mortis. Morphological studies have revealed significant increases in fiber size, in addition to structural irregularities in PSE muscle. These structural irregularities include decreased capillary density, hypercontracted (giant) fibers, and myoplasmic calcium loading. The common theme between poultry and swine in the development of PSE muscle is predominately in anaerobic fast-twitch muscles with low energy lactate metabolism yet accelerated onset of rigor mortis.     

肌纤维类型与肉嫩度的关系

阐述了肉的肌纤维与宰后嫩度形成之间的联系,发现由于肌肉宰后消耗能量、产生代谢产物与活体具有不一样的方式,而这个方式因肌纤维差异而存在不同之处,这就会影响到肌肉宰后能量与代谢水平的平衡,进而对肌肉宰后成熟产生调控作用,最终极有可能影响其嫩度的形成。      

Skeletal muscle fiber type and myofibrillar proteins in relation to meat quality

Although numerous studies have reported the relationships among muscle fiber characteristics, lean meat content and meat quality, controversial perspectives still remain. Conventional histochemical classifications may be involved in a high level of error, subjectivity and it could not clearly explain variety of myofibrillar protein isoforms. Therefore, more information is needed on how different factors, such as species, breeds, gender, nutrient conditions, physiological state of animals, and environment factors, affect ultimate meat quality in order to evaluate these uncertainness. Unfortunately, there is little information that completely covers with relationship among the muscle fiber types, myofibrillar proteins and enzymatic proteolysis. In addition to the perspective of postmortem metabolism, protein quality control in skeletal muscle and proteolytic degradation of muscle proteins during postmortem period could help to clarify this relationship. Therefore, the present review will focus on muscle fiber types, typing methods, muscle proteins and meat quality, and will summarize aspects of enzymatic view of proteasome.     

小分子热应激蛋白与肉嫩度的关系研究进展

肉嫩度的形成与动物宰后肌肉成熟过程中发生的复杂生理生化变化密切相关。动物宰杀放血后,氧气和营养物质供应终止,细胞凋亡程序启动,因此,调控该过程的凋亡因子可能最终影响到肌肉品质。小分子热应激蛋白（small heat shock proteins,sHSPs）作为肌肉嫩度的潜在生物标记,在许多蛋白组学的研究中得到证实。sHSPs由于其抗细胞凋亡和分子伴侣功能特性,在保护肌原纤维蛋白、干扰凋亡通路信号、延缓内源性蛋白酶对其的降解、延长肉的成熟时间等方面起到重要作用,与肉嫩度密切相关。本文综述了sHSPs作为肌肉向食用肉转变过程中的分子伴侣和其抗凋亡作用对肉嫩度的影响及其作用机理。     

Contribution of postmortem muscle biochemistry to the delivery of consistent meat quality with particular focus on the calpain system

Tenderness has been repeatedly reported as the most important quality aspect of meat. However, a number of studies have shown that a significant portion of retail meat can be considered tough. As a consequence, a significant consumer segment is willing to pay a premium for guaranteed tender meat. However, apart from measuring the shear force, there is no reliable method to predict tenderness. Most of the branded meat programs therefore attempt to ensure eating quality by controlling some of the factors that affect tenderness. Meat tenderness is determined by the amount and solubility of connective tissue, sarcomere shortening during rigor development, and postmortem proteolysis of myofibrillar and myofibrillar-associated proteins. Given the effect of postmortem proteolysis on the muscle ultrastructure, titin and desmin are likely key substrates that determine meat tenderness. A large number of studies have shown that the calpain proteolytic system plays a central role in postmortem proteolysis and tenderization. In skeletal muscle, the calpain system consists of at least three proteases, μ-calpain, m-calpain and calpain 3, and an inhibitor of μ- and m-calpain, calpastatin. When activated by calcium, the calpains not only degrade subtrates, but also autolyze, leading to loss of activity. m-Calpain does not autolyze in postmortem muscle and is therefore not involved in postmortem tenderization. Results from a number of studies, including a study on calpain 3 knockout mice, have shown that calpain 3 is also not involved in postmortem proteolysis. However, a large number of studies, including a study on μ-calpain knockout mice, have shown that μ-calpain is largely, if not solely, responsible for postmortem tenderization. Research efforts in this area should, therefore, focus on elucidation of regulation of μ-calpain activity in postmortem muscle. Discovering the mechanisms of μ-calpain activity regulation and methods to promote μ-calpain activity should have a dramatic effect on the ability of researchers to develop reliable methods to predict meat tenderness and on the meat industry to produce a consistently tender product.     

活性氧激活缺氧诱导因子-1α加速宰后成熟初期牛肉能量代谢

为探究活性氧（reactive oxygen species,ROS）在宰后成熟初期调控牛肉缺氧诱导因子-1α(hypoxiainduciblefactor-1α,HIF-1α)对能量代谢的影响。牛肉样品分别用H2O2、N-乙酰半胱氨酸（N-acetyl-L-cysteine,NAC）和生理盐水（对照）处理。在低温成熟0.5、6、12、24、48 h分别测定ROS含量、脯氨酰羟化酶（proline hydroxylase,PHD）活力、磷酸肌醇-3激酶（phosphatidylinositol3-kinase,PI3K）/蛋白激酶B(proteinkinase B,AKT)和HIF-1α蛋白质表达水平、能量代谢水平以及pH值的变化。结果发现：H2O2处理组初始（0.5 h）ROS含量显著高于其他2组（P<0.05）,且在48 h内始终处于显著较高水平（P<0.05）,NAC处理能够在短期内（0.5～12 h）抑制ROS积累;H2O2处理组PHD活力在0.5～48 h内显著低于其他2组（P<0.05）,同时,在0.5～12 h和0.5～6 h内PI3K和磷酸化AKT表达...     

Pre-slaughter transport, AMP-activated protein kinase, glycolysis, and quality of pork loin

Numerous studies have revealed that pre-slaughter stress, like transport, increases the occurrence of pale, soft, and exudative (PSE) pork meat. The molecular mechanism underlying this phenomenon, however, is poorly defined. In this study, we investigated the effects of pre-slaughter transport and subsequent rest on energy metabolism, AMP-activated protein kinase (AMPK) activation, and glycolysis in postmortem pork loin. Results indicated that pre-slaughter transport accelerated ATP depletion, which led to lower energy status in postmortem muscle immediately post-exsanguination when compared with control. The lower energy status led to AMPK activation within 1h postmortem, subsequently increasing glycolysis, leading to rapid glycolysis and high incidence of PSE meat. Allowing pigs to rest after transport restored energy status in muscle ante-mortem. Higher energy status then prevented premature and rapid AMPK activation in postmortem muscle and lessened the negative effects of pre-slaughter transport on meat quality. AMPK regulated glycolysis in postmortem muscle, at least partially, through phosphorylation and activation of phosphofructose kinase-2, since fructose-2,6-diphosphate content, an allosteric activator of phosphofructose kinase-1, was well correlated with AMPK activation and glycolytic rate. This suggests that AMPK is a potential molecular target for the control of PSE incidence in pork.     

Progress in reducing the pale, soft and exudative (PSE) problem in pork and poultry meat

Research in the area of the pale, soft and exudative (PSE) pork and poultry meat is reviewed in this article with an emphasis on genetic, biochemical and metabolic factors contributing to the problem. Over the past five decades, there has been much more work in the pork meat area where a few genetic markers have been identified, and are currently used to remove susceptible animals from the herd. Some of the markers are linked to aberrant calcium regulation in the early postmortem muscle. The poultry industry is still not at the point of using genetic marker(s); however, some recent work has revealed several potential markers. The review also discusses environmental factors such as antemortem stress and early postmortem processing practices (e.g. chilling rate) that can influence the development and severity of the PSE phenomenon. Some of these factors are known to cause protein denaturation at the early stage of postmortem and directly contribute to poor water-holding capacity and inferior texture in fresh meat and later in processed products. A newer hypothesis suggesting that variation in protein oxidation, in response to antemortem stress and early postmortem tissue environment, can contribute to development of PSE pork is also discussed. Finally, a few recommendations for future work are proposed.     

Biochemistry of postmortem muscle — Lessons on mechanisms of meat tenderization

It is certain that meat tenderness is a highly valued consumer trait and thus definition of the multiple processes that influence meat tenderness will provide clues toward improving meat quality and value. The natural process by which meat becomes tender is complex. Tenderness development is dependent on the architecture and the integrity of the skeletal muscle cell and on events that modify those proteins and their interaction. Specifically protein degradation and protein oxidation have been identified as processes that modify proteins as well as the tenderness of meat. The intracellular environment is a major factor that controls these events. Ultimately, the interplay between these events determines the rate and extent of tenderization. Given the intricacy of the structure of the muscle cell, coupled with the complexity of the regulation of protein modification and the ever-changing intracellular environment it is not surprising that this area of research is a very dynamic field. Just as the overall integrity and function of muscle cells does not depend on a single protein, but rather on the coordinated interaction of several proteins, the structural weakening of muscle cells during postmortem aging also must not depend on the degradation of a single myofibrillar or other cytoskeletal protein. The proteins mentioned in this review are located in different regions of the muscle cell, and most have been implicated in some manner as being important in maintaining the structure and function of the muscle cell. Oxidation of myosin heavy chain, a predominant protein in the myofibril, is known to promote aggregation and toughening of meat. Degradation of proteins such as desmin, filamin, dystrophin, and talin (all located at the periphery of the Z-line) may disrupt the lateral register and integrity of the myofibril themselves as well as the attachments of the peripheral layer of myofibril to the sarcolemma. Degradation of the proteins within the myofibril that are associated with the thick and thin filaments may allow lateral movement or breaks to occur within the sarcomeres of postmortem aged samples. Titin, nebulin, and troponin-T, by their ability to directly interact with, or modulate the interaction between, major proteins of the thick and thin filaments and (or) the Z-line, play key roles in muscle cell integrity. Disruption of these proteins, especially titin and nebulin, could initiate further physicochemical and structural changes that result in myofibril fragmentation and loss of muscle cell integrity, and ultimately in tenderization of the muscle. In order to make real progress in this area, the scientific community must have a global appreciation of how both the structural proteins and the key proteases are influenced by the vast changes that occur during the conversion of muscle to meat.     

Postmortem changes in muscle electrical properties of bovine M. longissimus dorsi and their relationship to meat quality attributes and pH fall

Heifers (n=47) were slaughtered and hung conventionally in an industrial meat plant. Electrical impedance (Py) and conductivity (EC) were studied for their ability to indicate or predict selected meat quality attributes i.e. Warner-Bratzler shear force (WBSF), sensory tenderness, texture, flavour and acceptability, water holding capacity (WHC) and colour. pH, electrical impedance (meat check) and electrical conductivity (pork quality meter) measurements were taken at hourly intervals up to 8 h and again at 1 and 2 days postmortem. Electrical measurements were taken again at 7 and 14 days postmortem. Freshly cut steaks (2.5 cm thick) were taken from the longissimus dorsi (LD) muscle at 2, 7 and 14 days postmortem, vacuum-packaged in plastic bags and stored at -20°C for WBSF and sensory analysis. Freshly cut steaks were used for WHC and colour measurements. During the development of rigor and over the ageing period, electrical changes occur in muscle tissue. Electrical measurements were found to change significantly between 1 and 14 days postmortem and when measured over the ageing period (at 2, 7 and 14 days postmortem) were significantly correlated to WBSF, sensory tenderness and Hunter 'a' and 'b' values (r=±0.56-±0.68, p<0.001) and weakly to moderately correlated to other sensory attributes (r=±0.31-0.58, p<0.001) measured at the same times postmortem; thus showing potential for these rapid physical measurements as indicators of meat quality if both electrical measurements and quality attributes are measured at the same times postmortem and correlations are calculated over the ageing period. However, electrical measurements taken at specific times at the early postmortem period (i.e. at 1 or 2 days) showed only a few weak relationships with meat quality attributes measured at later times postmortem (i.e. 7 or 14 days) demonstrating that early postmortem electrical measurements are not suitable for the prediction of ultimate meat quality. Py values taken between 7 h and 7 days postmortem were significantly correlated with all pH measurements with the exception of 1 day values. Two day Py measurements showed the highest correlations (r=0.45-0.62, p<0.01-0.001) with pH. EC was also found to be moderately correlated with pH although correlations were slightly lower than those obtained for Py. Highest correlations (r=0.47-0.59, p<0.01) were obtained for 7 h values.     

秦川牛肉冷藏期间能量代谢变化及其对肉品质的影响

为探究秦川牛肉在冷藏期间能量代谢机理及其对肉品质的影响。采用4D-非标记定量蛋白质组学法研究不同贮藏期（0、4、8 d）秦川牛背最长肌中蛋白质组学变化,采用高效液相色谱法检测能量物质的变化。结果表明：与能量代谢相关的三磷酸腺苷（adenosine triphosphate,ATP）合酶亚基δ和ATP合酶亚基γ在贮藏第8天时较第0天分别上调1.516（P＝0.017）、1.579 倍（P＝0.037）;NADH脱氢酶[泛醌]1β亚复合物亚基5在贮藏第8天时较第4天调整0.497 倍（P＝0.023）;琥珀酸-辅酶A连接酶[ADP形成]亚基β在贮藏第8天时较第0天调整0.762 倍（P＝0.000 7）;NADH脱氢酶[泛醌]1α亚复合物亚基6在贮藏第4天时较第0天上调1.467 倍（P＝0.026）;细胞色素c氧化酶亚基7A1在贮藏第8天时较第4天调整0.692 倍（P＝0.024）。以上6 种蛋白表达丰度的变化通过线粒体电子传递、呼吸链复合物I装配、ATP生物合成等过程影响ATP等能量物质合成和运输过程,导致冷藏期间肌细胞中能量物质供应不足,进而影响肉品质的变化：在贮藏0～8 d期间ATP含量降低了95.07%,影响了肌红蛋白的转化,导致褐变出现;促使无氧糖酵解在产能的同时产生乳酸,引起肌肉酸化;导致细胞凋亡,肌原纤维蛋白水解促使肌肉嫩度变化。     

蛋白质磷酸化对宰后肉品质影响研究进展

畜禽肌肉在宰后变为可食肉的过程中,需要经过一系列的生化变化直到成熟,其中蛋白质磷酸化反应作为一种蛋白质的动态调控机制,几乎调节每一个主要的生物过程,是生物界常见的翻译后修饰形式之一。因此,研究蛋白质磷酸化与宰后肌肉的关系有助于肉类食品行业的发展。本文从介绍蛋白质磷酸化概念出发,讨论磷酸化蛋白质检测技术的发展,总结宰后肌肉中会发生磷酸化的蛋白质及影响因素,从蛋白质磷酸化反应与宰后肉的嫩度、肉的色泽和保水性3 个方面的研究入手综述蛋白质磷酸化反应对肉品质的影响,以及食盐与氨基酸在该过程中的应用,并对蛋白质磷酸化反应在肉品品质中的研究做出展望。