正常肉和白肌肉的蛋白质变化

测定白肌肉(Pale,Soft,Exudative,PSE)和正常猪肉(Reddish-pink,Firm,Non-exudative)持水性指标和在宰后不同时间的蛋白溶解性和蛋白降解程度。结果显示:PSE肉的各种蛋白溶解性都显著低于正常肉(p<0.05),宰后4 h的总蛋白、肌浆蛋白和肌原纤维蛋白的溶解性与滴水损失和贮藏损失都呈显著负相关,与持水力呈显著正相关。正常肉和PSE肉的肌浆蛋白和肌原纤维蛋白的SDS-PAGE电泳条带存在差异,PSE肉早期伴肌动蛋白(Nebulin)含量明显低于正常肉。可见PSE肉肌原纤维的降解较快,宰后早期的蛋白溶解性可以用于预测猪肉的持水性。     

猪宰后不同部位白肌肉与正常肉品质变化、能量代谢的差异

对猪宰后不同部位白肌(pale soft exudative,PSE)肉与正常肉的品质变化及能量物质的代谢差异进行研究。选取"杜长大"阉公猪宰后背最长肌、股二头肌均为正常肉和PSE肉,测定不同时间点肉品质指标(pH值、离心失水率、剪切力、L*)及能量物质(糖原、腺苷三磷酸(adenosine triphosphate,ATP)、腺苷二磷酸、腺苷酸)含量的变化,并分析各自的相关性。结果表明:宰后2 h内,股二头肌ATP含量显著高于背最长肌(P0.05)。宰后8 h内所有样本ATP含量下降显著(P0.05);宰后48 h内,正常肉股二头肌糖原含量显著高于其他样本(P0.05);离心失水率变化和L*值变化呈正相关(P0.01);糖原含量和ATP含量的变化呈正相关(P0.01)。因此,股二头肌肉品质优于背最长肌,股二头肌的糖原、ATP含量高于背最长肌,背最长肌能量代谢速率高于股二头肌。     

PSE猪肉肌原纤维蛋白的氧化变性

为探讨白肌肉(pale,soft and exudative meat,PSE肉)形成时肌原纤维蛋白结构和功能的变化,以PSE猪肉为研究对象,从氧化还原体系失衡和钙激活蛋白酶活性变化两方面进行研究。结果表明:与正常肉(red,firm and non-exudative meat,RFN肉)相比,PSE肉的超氧化物歧化酶抑制率显著降低(P0.05),谷胱甘肽过氧化物酶活性显著增加(P0.01),钙激活蛋白酶活性显著增加(P0.05);随着氧化还原体系失衡和钙激活蛋白酶活性的增加,PSE肉十二烷基硫酸钠-聚丙烯酰胺凝胶电泳图谱的肌间线蛋白、肌动蛋白和Ⅰ-肌钙蛋白条带变淡、变细;肌原纤维蛋白的表面疏水性显著增大(P0.05),溶解性显著降低(P0.01),结构和功能特性发生改变。     

腌制温度对羊肉蛋白质磷酸化水平的影响

研究了不同腌制温度对羊肉肌原纤维蛋白和肌浆蛋白磷酸化水平的影响。取宰后排酸24 h的胴体米龙,设定-1℃、4℃和25℃三个腌制处理组,取腌制0 h、8 h、16 h和24 h的样品,采用SDS-PAGE电泳与荧光染色相结合的方法分析磷酸化水平的变化。结果表明,腌制温度越低,肌原纤维蛋白整体磷酸化水平(P/T值)越高,腌制8 h时,冰温组整体磷酸化水平显著高于室温组(p0.05),腌制16 h和24 h时无显著差异。而肌浆蛋白磷酸化水平结果与之相反,腌制温度越低,肌浆蛋白质整体磷酸化水平越低。腌制8 h时,冰温腌制组整体磷酸化水平显著低于室温腌制组(p0.05),腌制16 h和24 h时也无显著差异。单个蛋白条带呈现差异,随着腌制温度的升高,肌动蛋白和醛缩酶磷酸化水平升高,肌球蛋白和烯醇酶磷酸化水平降低。因此,腌制温度可能通过影响蛋白质磷酸化,进而调控肉的品质。     

肉牛宰后初期一磷酸腺苷活化蛋白激酶活性在不同部位肉中的差异表达及与牛肉品质关系

文中主要探讨了一磷酸腺苷活化蛋白激酶(adenosine monophosphate-activated proteinkinase,AMPK)在宰后早期(3、5.5、7和10 h)不同部位牛肉中的差异性表达以及对最终牛肉品质的影响。选取牛柳(psoas major,PM)与西冷(longissimus dorsi,LD)2个部位,分别测定p H值、AMPK活性、糖酵解指标和肉品质指标。研究结果表明:随着宰后时间的延长,AMPK的活性显著下降(P0.05),而且PM中的AMPK活性显著高于LD(P0.05);AMPK活性与p H值与肌糖原含量呈显著正相关,与乳酸含量及(AMP+IMP)/ATP[AMP:adenosine monophosphate,一磷酶腺苷;IMP:inosine monophosphate,肌苷酶;ATP:adehosine triphosphate,三磷酶腺苷)呈显著负相关关系(P0.05),丙酮酸激酶随宰后时间先升高后降低(P0.05),而且PM中丙酮酸激酶达到最大活性值的时间以及最大值要早于且高于LD(P0.05);同时,PM在成熟期间表现出较高的嫩度以及较低的蒸煮损失(P0.05)。上述结果表明,AMPK能够通过调节糖酵解进程而影响牛肉的品质。     

猪宰后正常肉与PSE肉中肌间线蛋白和钙激活酶的变化与持水性的关系

通过运用蛋白质印迹技术(Western blot)研究猪肉宰后正常肉与PSE肉的肌间线蛋白(Desmin)和钙激活酶(μ-calpain)与持水性的关系,旨在为分析猪肉持水性的形成机制提供参考。结果显示:宰后正常肉组与PSE(Pale,Soft,Exudative)组的Desmin均随着时间的增加而发生降解,到宰后3~5 d,RFN(Reddish-pink,Firm,Non-exudative,正常肉)组的Desmin的降解量与PSE组的Desmin降解量差异显著(p0.05)。RFN组的Desmin在宰后5 d出现明显降解(p0.05);PSE组在宰后3 d出现明显降解(p0.05)。宰后猪肉样品的汁液流失率与在宰后3、5 d Desmin完整度呈显著负相关(p0.05)。μ-calpain与宰后Desmin完整度之间呈正相关,其中76 ku亚基与宰后5 d的Desmin完整度之间呈显著负相关(p0.05)。结论:μ-calpain活性越高,Desmin降解越多,汁液流失率越大。     

蛋白质组学揭示宰前温和驱赶改善猪肉品质的潜在机制

宰前不同驱赶方式对生猪造成不同程度应激,进而影响猪肉品质。本实验以45头6月龄大的生猪为研究对象,随机分配到完全温和驱赶组(全温组,n=15)、声音温和驱赶组(声温组,n=15)和传统驱赶组(传统组,n=15)。宰后测定生猪血液应激指标、肌肉品质和理化指标,并利用蛋白质组学鉴定影响宰后肌肉能量代谢与肉品品质的调控蛋白,探索宰前驱赶影响肉品品质的潜在机制。结果表明:相比于传统组,全温组的肌酸激酶、乳酸脱氢酶、皮质醇含量显著下降(P0.05),应激程度最低;红度a*值显著升高(P0.05),蒸煮损失率显著降低(P0.05),PSE(pale, soft, exudative)肉发生率下降;宰后45 min和3 h的pH值显著提高(P0.05);宰后45 min和3 h的ATP含量显著增大(P0.05)。相似地,声温组应激水平也低于传统组,其肌酸激酶、乳酸脱氢酶活力、45 min和3 h的pH值、45 min和3 h的ATP含量等指标都处于中间水平。此外,蛋白质组学鉴定出46个差异蛋白,包括能量代谢相关的ATP依赖性6-磷酸果糖激酶、α-1,4-葡聚糖磷酸化酶、糖原脱支酶、甘油醛-3-磷酸脱氢酶、磷酸甘油酸激酶、异柠檬酸脱氢酶、线粒体肌酸激酶2以及肌肉收缩相关的肌球蛋白7。两组温和驱赶方式都减缓肌肉中的能量代谢进程并改变肌肉收缩状态,进而提高宰后肌肉pH值、糖原和ATP水平,最终改善猪肉品质。     

溶液环境对PSE猪肉肌原纤维蛋白溶解度及热诱导凝胶强度的影响

以正常猪肉和PSE 猪肉背最长肌为材料,采用分光光度法、物性测定法和SDS-PAGE 凝胶电泳法研究pH值、NaCl 浓度和三聚磷酸钠(TPP)浓度对肌原纤维蛋白溶解度和凝胶强度的影响。结果表明：pH 值、NaCl 浓度和三聚磷酸钠浓度对猪肉肌原纤维蛋白质的溶解性和凝胶强度均有显著影响(P ＜ 0.05),改善体系环境、提高蛋白质溶解度可提高PSE 肉凝胶功能特性。     

不同嫩度羊肉肌浆蛋白质磷酸化水平随宰后成熟时间变化的研究

本文研究了不同嫩度羊肉肌浆蛋白磷酸化水平随宰后成熟时间的变化。取40只羊宰后0.5 h、1 h、4 h、12 h、24 h背最长肌样品,根据24 h剪切力和肌原纤维小片化指数分为高嫩度组和低嫩度组。采用SDS-PAGE电泳、荧光染色等方法,分析肌浆蛋白的磷酸化水平。研究结果表明在宰后24 h内肌浆蛋白磷酸化水平在不同嫩度和宰后成熟时间处理组之间差异显著(P0.05),低嫩度组的整体蛋白质磷酸化水平在宰后4 h达到最大,高嫩度组的整体蛋白质磷酸化水平在宰后12 h达到最大。宰后0.5 h、1 h、4 h低嫩度组的肌浆蛋白整体磷酸化水平显著高于高嫩度组(P0.05)。因此,肌浆蛋白磷酸化水平受不同嫩度和宰后成熟时间处理影响显著(P0.05),磷酸化可能通过对宰后肌肉糖酵解的作用影响宰后肌肉僵直进程,进而影响肌肉嫩度。     

AMPK活性对宰后牛肉糖酵解、肌肉内环境及品质的影响

为探究牛肉宰后成熟过程中单磷酸腺苷活化蛋白激酶（adenosine monophosphate-activated protein kinase,AMPK）对糖酵解、肌肉内环境及品质的影响,以0.50 mol/L 5-氨基咪唑-4-甲酰胺核苷（5-amino-4-imidazolecarboxamide,AICAR）处理的西杂牛背最长肌为对象,于4 ℃进行成熟,测定宰后成熟期间肌肉AMPKα基因（PRKAA1、PRKAA2）转录量、P-AMPK表达量、AMPK活性、糖酵解水平及品质指标的变化情况。结果表明：宰后24～120?h,处理组AMPKα基因转录量、P-AMPK表达量及AMPK活力均显著高于对照组（P＜0.05）;72～168?h,处理组pH值和肌糖原含量显著低于对照组（P＜0.05）,乳酸含量显著高于对照组（P＜0.05）;12～168?h,处理组L*、b*值及ATP、ADP、AMP和IMP含量均显著高于对照组（P＜0.05）,a*值显著低于对照组（P＜0.05）;24～120?h,处理组蒸煮损失率和肌原纤维小片化指数显著高于对照组（P＜0.05）,剪切力显著低于对照组（P＜0.05）。AICAR通过激活AMPK并加快宰后糖酵解影响肌肉内环境、肉色、剪切力及肌纤维微观结构变化,加快宰后肌肉成熟进程,说明AMPK活性对宰后肌肉糖酵解及品质变化具有重要影响,且可通过调控宰后肌肉AMPK活性来调节肌肉品质。     

Sarcoplasmic proteins influence water-holding capacity of pork myofibrils

Water-holding capacity (WHC) is one of the main pork quality characteristics. The objective of this study was to determine the influence of (denaturation of) sarcoplasmic proteins on WHC. Myofibrils extracted from red, firm, non-exudative (‘normal’) and PSE (pale, soft, exudative) pork longissimus muscle were combined with sarcoplasmic extracts (with or without proteins) from PSE and normal pork longissimus samples. Weight increase of myofibrils (mg increase mg⁻¹ myofibrillar protein) was used as a measure of WHC. When combined with protein-containing sarcoplasmic extract from normal pork, WHC of myofibrils from PSE (2.6 mg mg⁻¹) and normal (2.8 mg mg⁻¹) pork was higher (P < 0.05) than when combined with sarcoplasmic extract from PSE meat (1.3 mg mg⁻¹ for PSE and 1.9 mg mg⁻¹ for normal myofibrils). Protein-free sarcoplasmic extracts were prepared by heating the extracts for 30 min at 80 °C. WHC of myofibrils combined with protein-free sarcoplasmic extract from PSE and normal pork was not significantly different. WHC of myofibrils combined with protein-free extract was lower than WHC of myofibrils combined with protein-containing extract. Ionic strength or pH could not explain the observed differences. It was concluded that sarcoplasmic proteins do influence WHC. The mechanism of this influence still needs to be determined. © 1999 Society of Chemical Industry     

The relationship of sarcoplasmic and myofibrillar protein solubility to colour and water-holding capacity in porcine longissimus muscle

In order to investigate the relationship of sarcoplasmic and myofibrillar protein solubility to colour and water-holding capacity (WHC) in pork, 60 loins were selected to represent the quality classes: PSE (pale, soft, exudative), RSE (reddish-pink, soft, exudative), RFN (reddish-pink, firm, non-exudative) and DFD (dark, firm, dry). PSE samples exhibited lower (p<0.05) protein solubility (sarcoplasmic, myofibrillar and total) compared to the other quality classes. RSE samples exhibited lower (p<0.05) sarcoplasmic protein solubility compared to DFD samples. RSE, RFN and DFD samples had similar myofibrillar and total protein solubilities. Sarcoplasmic protein solubility explained 71% of the variation in lightness with a linear decrease in L* value. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) gels of the sarcoplasmic and myofibrillar samples distinctly showed the association of some sarcoplasmic proteins with the myofibrillar protein fractions in PSE and RSE samples. The sarcoplasmic proteins which precipitated were phosphorylase, creatine kinase, triose phosphate isomerase and myokinase for PSE and phosphorylase for RSE samples. Pork colour is highly correlated with precipitation of sarcoplasmic proteins while WHC is affected by denaturation of myofibrillar proteins (PSE samples) and lower ultimate pH (PSE and RSE samples).     

Biochemical Properties of Natural Actomyosin Extracted from Normal and Pale, Soft, and Exudative Pork Loin After Frozen Storage

ABSTRACT: The studies of natural actomyosin (NAM) extracted from normal and pale, soft, and exudative (PSE) pork longissimus muscle stored at -20°C for up to 6 mo, revealed that the surface hydrophobicity (S₀-ANS) of NAM from PSE pork was significantly ( P < 0.05) higher than that from normal pork indicating greater conformational changes in proteins from PSE meat that resulted in the exposure of hydrophobic aromatic amino acid residues on the surface. Also, the S₀-ANS of NAM was a function of storage time. The equations were as follows: S₀-ANS = 16.9 × storage mo + 123 for normal and S₀-ANS = 17.5 × storage mo + 164 for PSE. NAM from frozen normal pork had lower α-helical content than comparable fresh pork. With extended frozen storage, viscosity of NAM from PSE meat was lower than that from normal pork. The sulfhydryl and disulfide contents were unchanged. Electrophoresis revealed an extra 95 to 100 kDa band from PSE meat NAM, possibly from α-actinin or myosin degradation. Water-binding capacity (WBC) of normal and PSE meat decreased with increasing storage time; however, there were only minor changes in thaw loss. The decrease of WBC of pork meat partially can be explained by the increase of S₀-ANS observed for the NAM. These results suggest that proteins from PSE pork are more susceptible to denaturation and degradation in fresh meat and following frozen storage.     

Quality characteristics of Chinese sausages made from PSE pork

Chinese sausages made from normal and different levels of PSE pork (100% Normal, 50%Normal+50% PSE and 100% PSE) were vacuum-packaged and stored at 4 °C for 45 days. The composition, processing yield, pH value, thiobarbituric acid (TBA) value, water activity, lactic acid bacteria counts and sensory properties of the meat products were evaluated. PSE pork loins had lower pH value, water holding capacity, moisture, fat and myofibrillar proteins content, but higher L^* value, drip loss and protein content than normal pork. Sausages made from 100% PSE pork had lower pH value, processing yield, moisture and fat content, but higher protein content than those of the 100% Normal and the 50% Normal+50% PSE treatments. Water activity was higher in the 100% PSE treatment than in other treatments. No differences in lactic acid bacterial counts among these treatments were observed. The pH values and water activity of the meat samples decreased, while lactic acid bacterial counts increased with storage time. TBA values among these treatments were not significantly different; however, the increase% of TBA values was higher for the 100% PSE treatment. TBA values of all treatments remained relatively low during storage. Chinese sausages made with 50–100% PSE pork had lower sensory texture, flavor and overall acceptability scores than the control samples, but were of acceptable quality.     

加工工艺对酱牛肉蛋白质结构和水分分布的影响

为深入了解酱牛肉加工过程中蛋白质结构变化,借助酶标仪、扫描电子显微镜、傅里叶红外光谱仪、核磁共振分析仪等设备,以蛋白浊度、分子间相互作用力、微观结构、二级结构变化和水分分布为指标,对酱牛肉加工过程中（原料、滚揉腌制、卤制）和不同温度二次杀菌（90、100、110、120 ℃）的样品进行分析。结果：酱牛肉样品中提取的肌原纤维蛋白浊度高于肌浆蛋白浊度,滚揉腌制可显著降低肌浆蛋白和肌原纤维的蛋白浊度（P＜0.05）,热处理使蛋白浊度升高;滚揉腌制提高了蛋白质分子间相互作用力,热处理降低了蛋白质分子间静电相互作用,氢键、疏水相互作用和二硫键是样品中主要分子间作用力;不同加工处理对样品中肌浆蛋白和肌原纤维蛋白的结构均有破坏,随加工工艺增多（滚揉腌制、卤制、二次杀菌）破坏程度增大,且二次杀菌温度越高,蛋白质结构破坏越严重;滚揉腌制、卤制、二次杀菌对蛋白质二级结构有明显影响;二次杀菌酱牛肉样品中,经100 ℃杀菌后自由水含量和总水分含量最高,不同杀菌温度对束缚水含量的影响不显著（P＞0.05）。     

Muscle protein changes post mortem in relation to pork quality traits

The relationship between post-mortem traits of muscle proteins and water loss traits was investigated using 84 pork loins representing the four quality traits of PSE, RSE (reddishpink, soft, exudative), RFN (reddish-pink, firm, non-exudative) and DFD. Protein solubility measurements (sarcoplasmic, myofibrillar and total) were lower and myosin denaturation (quantified by myofibrillar ATPase activity) was higher for PSE samples compared with samples from the other quality classes. RSE samples were similar to RFN samples in protein solubility and myosin denaturation, although RSE had lower values then DFD samples for protein solubility measurements. RFN samples had lower drip, thaw, cook and total water loss than RSE samples and all water loss traits were lowest for DFD samples and highest for PSE samples. Insoluble phosphorylase was the only characteristic that differentiated among PSE, RSE and RFN samples. SDS-PAGE and Western blots indicated that in PSE and RSE samples, the myofibrillar protein titin was less degraded and nebulin was more degraded compared with RFN and DFD samples. SDS-PAGE of extracted and unextracted myofibrils showed that the reduced myofibrillar solubility of PSE samples was caused by decreased extractability of the myosin heavy chain in these samples. In conclusion, although RSE samples have unacceptably high water loss, muscle protein denaturation was minimal and did not explain the low water-holding capacity.     

猪肉蛋白和牛肉蛋白对生长期大鼠生理功能的影响

目的：研究长期摄入猪肉蛋白和牛肉蛋白对生长期大鼠生长性能、生理功能的影响。方法：30 只雄性Sprague-Dawley（SD）大鼠随机分为3 组,分别饲喂添加酪蛋白、猪肉蛋白和牛肉蛋白作为蛋白质来源的半合成饲料,实验期为90 d,观察其对大鼠生理指标的影响。结果：相对于酪蛋白组,猪肉蛋白组和牛肉蛋白组大鼠的生长速率变缓,脂肪沉积减少（P＜0.05）,但有较高的谷丙转氨酶和谷草转氨酶活力（P＜0.05）。猪肉蛋白和牛肉蛋白可降低大鼠血清中的甘油三酯浓度（P＜0.05）,牛肉蛋白还可降低总胆固醇和血糖浓度（P＜0.05）,猪肉蛋白则对其没有显著影响（P＞0.05）。猪肉蛋白组和牛肉蛋白组的大鼠有较低的血清游离氨基酸水平（P＜0.05）。结论：长期摄入猪肉蛋白和牛肉蛋白会对大鼠机体代谢产生不同的影响,这与蛋白质来源及其消化和吸收有关。猪肉蛋白和牛肉蛋白有控制大鼠体质量增长的作用,牛肉蛋白还可以降低大鼠肝脏代谢水平,具有降血脂的功能。     

Iron-binding properties, amino acid composition, and structure of muscle tissue peptides from in vitro digestion of different meat sources

ABSTRACT:  Background: The enhancing effect of meat on nonheme iron bioavailability in humans is thought to be due to the release of low-molecular-weight (LMW) iron-binding peptides during digestion. Objective: To better characterize the LMW iron-binding peptides from meat digests. Methods: Cooked beef, chicken, cod, lamb, and pork myofibrillar or sarcoplasmic protein extracts, casein, and egg albumin were digested in vitro with pepsin or pepsin/pancreatin. Ultrafiltrates were analyzed for N and iron and further characterized by gel filtration with added ⁵⁹Fe, amino acid analysis, and LC-MS. Results: 84% to 98% of total iron in enzymic digests was associated with soluble LMW peptides (< 10 kDa) of the myofibrillar proteins compared to only 2% to 20% in the corresponding sarcoplasmic protein digests. Pepsin digestion alone of the myobrillar proteins generated > 80% soluble LMW iron, compared to < 5% with casein and egg albumin. Iron-binding peptides from myofibrillar protein with an estimated 2 kDa molecular mass were separated by gel filtration. Peptides in this fraction were enriched in aspartic and glutamic acid residues and included potential peptide fragments of myosin. Conclusion: LMW (< 10 kDa) peptides in enzyme digests of myofibrillar proteins were the major facilitators of iron solubility. Unlike with casein, egg albumin, and most sarcoplasmic proteins, these LMW peptides were generated on pepsin digestion. One group of iron-binding peptides had a mass of approximately 2 kDa and was enriched in glutamic and aspartic acids. Such early generation of a multitude of LMW iron-binding peptides could explain the enhancing effect of muscle tissue on iron absorption.