超低温双螺旋速冻对猪背最长肌加工品质的影响

为研究超低温双螺旋速冻（Ultra-low Temperature Double Spiral Quick Freezing,UTDSQF）对原料猪肉加工品质的影响,该研究以宰后24 h且pH值在正常范围内的猪背最长肌为研究对象,分别采用常规空气冻结（Air-blast Freezing,AF）和超低温双螺旋速冻两种方式对猪背最长肌进行冻结,随后在-20 ℃冷库中冻藏90 d后于4 ℃解冻,加工制成乳化香肠,测定两种冻结方式对其理化、质构和感官品质的影响。研究表明：原料肉不同冻结方式对乳化肠pH值没有显著影响（P>0.05）;与AF组相比,UTDSQF组的TBARS值和蒸煮损失分别降低26.67%、31.25%（P<0.05）;L*值和a*值显著升高（P<0.05）,但b*值显著降低（P<0.05）;UTDSQF组的硬度、咀嚼性、回复性和内聚性显著升高（P<0.05）,而弹性没有显著性差异（P>0.05）;同时,UTDSQF处理原料肉显著提升了乳化肠的感官评分（P<0.05）。因此超低温双螺旋速冻处理能够整体提升原料肉的加工品质。     

猪背最长肌蛋白质在冷冻贮藏过程中的变化

为研究冻藏时间对猪背最长肌蛋白质特性的影响,本文主要采用凝胶电泳、差示量热扫描技术分析了猪背最长肌在-18 ℃冻藏0 d和1、3、6、9、12、15月后,其蛋白质的疏水性、巯基含量、降解情况、热稳定性的变化。结果表明:随冻藏时间的延长,蛋白质溶解度显著降低(p<0.05),肌原纤维蛋白(MPI)的表面疏水性和巯基含量升高,发生降解的MPI主要集中在67 kDa和20~29 kDa;肌球蛋白和肌浆蛋白的变性温度和焓值呈现逐渐降低的趋势,表明这两类蛋白的热稳定性降低。在冻藏的前3个月内,猪背最长肌的各项指标维持在较好的水平,从第6个月开始,所有指标的变化幅值增加,变化速率加快。研究发现,冻藏6个月以后,猪背最长肌蛋白质品质开始加速下降。     

快速与慢速解冻对冷冻猪肉品质特性及蛋白变性的影响

研究快速解冻技术(微波、超声)与慢速解冻技术(流水、空气、低温、35℃静水)对猪肉品质特性及蛋白质变性程度的影响,以新鲜猪肉作为对照组,分析六种解冻方式对冷冻肉,解冻速率、保水性、色泽、脂肪氧化程度(TBARS)、蛋白溶解性、蛋白变性程度、新鲜度及剪切力值的影响。结果表明,与新鲜猪肉相比,经解冻处理后,猪肉的品质特性均有不同程度的变化;经差示热量扫描仪(DSC)热分析也可看出,解冻方式对猪肉蛋白质的变性程度有一定影响。六种解冻方式中,微波解冻作为一种快速解冻方式,耗时最短,解冻速率为39.61 cm/h,与慢速解冻相比,大大提高了解冻效率(p<0.05),且能较好地保持猪肉的保水性和嫩度,解冻后猪肉的TBARS值和蛋白变性程度较低,新鲜度也仍在一级鲜肉的水平。由此说明,微波解冻能较好地保持猪肉的品质。     

Fatty Acid and Cholesterol Changes in Pork Longissimus Muscle and Fat due to Ractopamine

Fatty acid (FA) composition and cholesterol (CHL) content from control and Ractopamine (Rac) treated pigs were evaluated. Lipids were extracted from the longissimus (LD) and subcutaneous fat (SC) and methyl esters of the FA were formed for gas chromatography. CHL content of the LD was determined using direct saponification. Pigs were fed 0, 5, 10 or 20 ppm Rac for about 40 kg of grain prior to slaughter. Rac had no consistent effect on the FA composition of SC or muscle (neutral or polar) lipids. CHL content in the LD of treated animals was about 9% lower (P < 0.01) than controls. Rac reduced the CHL content of the LD and had limited effect on the FA profile of muscle or SC fat.     

蓄冷装置对猪肉冻结品质的影响

以新鲜猪背最长肌为原料,考察其在冻结条件①:冻结装置A+-18℃(风冷、无蓄冷板);冻结条件②:冻结装置A+-24℃(风冷、无蓄冷板);冻结条件③:冻结装置A+-24℃(风冷、加蓄冷板);冻结条件④:冻结装置B+-25℃(风冷、无蓄冷板)4种条件下冻结处理后,有无冻结装置对猪肉品质影响的差异性。结果表明,经4种冻结装置条件处理后,对于冻结条件③对猪背最长肌冻结效果优于同温度下冻结条件②冻结效果,优于冻结条件①冻结效果,即加蓄冷板冻结效果,优于不加蓄冷板,优于-18℃;冻结装置A加蓄冷板冻结效果与冻结装置B加-25℃(无蓄冷板)差异不显著(P>0.05)。整体来说,通过蓄冷装置冻结,能有效减少汁液流失、降低压榨损失,减少肌原纤维断裂与巯基破坏情况,促进肉品品质保持效果。     

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。     

Determination of Protein Denaturation of Muscle Foods Using the Dielectric Properties

ABSTRACT: Both the dielectric constant and loss factor increased at a temperature that appeared to match the DSC denaturation temperature for collagen in beef, chicken breast, chicken thigh, perch, cod, and salmon. When the sample was reheated the change did not reoccur, indicating that the dielectric properties were measuring an irreversible change. At lower frequencies the increase in the dielectric properties was larger. When collagen and acto-myosin denature, the muscle shrinks, expelling water and minerals. This makes the water and ions more mobile. The dielectric constant and loss factor measure the mobility of water and ions; therefore they may be able to determine the temperature of protein denaturation.     

Composition, Separation and Denaturation of Longissimus Muscle Proteins from Pigs Treated with Porcine Somatotropin (pSt)

Longissimus muscles from 36 pigs fed two different diets (16% or 19% protein) and injected daily with one of three levels (0, 4, or 8 mg/day) of recombinant porcine somatotropin (pSt) were evaluated for composition, myofibrillar protein characteristics and protein denaturation temperatures. Crude fat contents of the raw longissimus were 2.9, 2.5 and 1.8% for the pSt treatments, respectively. No differences in number of extracted proteins, calculated molecular weights or endothermic denaturation temperatures were attributed to pSt treatment. Cholesterol and iron contents of the cooked tissue were not affected by pSt treatment; thiamin content, however, decreased in response to pSt administration.     

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。     

Utilization of Pork Collagen Protein in Emulsified and Whole Muscle Meat Products

ABSTRACT: Effects of pork collagen in emulsified and whole muscle products were evaluated. Eight frankfurter treatments (0%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, and 3.5% pork collagen) and 4 ham treatments (0%, 1%, 2%, and 3% pork collagen) were formulated. Frankfurters and hams were evaluated for cooked yields, purge, color, texture, and sensory characteristics. Incorporation of pork collagen at 1% and above significantly ( P < 0.05) increased cooked and chilled yields in frankfurters but did not have any effect in hams. Purge was significantly ( P < 0.05) reduced in both frankfurters and hams after 4 wk of storage. Sensory difference testing showed no significant difference up to 2% usage level of pork collagen in both frankfurters and hams ( P > 0.05).     

Effect of Postmortem Storage on Degradation of the Myofibrillar Protein Titin in Bovine Longissimus Muscle

Purified bovine longissimus muscle myofibrils were prepared from muscle at death and from muscle samples stored at 2°, 25°, or 37°C for 1, 3, and 7 days postmortem. Tbe myofibrils were analyzed by sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis. Titin migrated as a closely spaced doublet of very high molecular weight (M_r～ 1 × 10⁶) in myofibrils from at-death muscle samples. With increased storage time and temperature, the top band of the titin doublet gradually disappeared. the lower doublet band (putative breakdown product of upper band) remained after 7 days storage at 2° or 25°C, but disappeared by 3 days of postmortem storage at 37°C. Thus, titin is degraded in postmortem muscle, and the rate of degradation is enhanced by increases in storage time and temperature.     

Protein Denaturation and Structural Damage During High-Pressure-Shift Freezing of Porcine and Bovine Muscle

ABSTRACT: Pork and beef muscles were subjected to 200 MPa and −20 °C with or without water freezing. Both tissues responded to the treatment with similar behavior. Protein denaturation was greater when freezing occurred. Pressure-induced cold denaturation was complete for actin and very considerable for myosin and other muscle proteins. Connective proteins remained practically unaltered by pressurization and/or freezing. Structural changes in the muscle at sarcomere levels caused by pressurization were more severe when freezing occurred. Color, drip loss, and textural properties on the pressurized samples also revealed an additional deleterious influence of freezing. Pressurization alone and pressure-shift freezing resulted unsuitable for muscle preservation.     

不同解冻方式对猪肉品质特性的影响

研究自然空气解冻、静水解冻、微波解冻和低温解冻4 种不同解冻方式对猪背最长肌肉品质特性的影响,分析猪肉解冻过程中食用品质特性、全质构特性、肌浆蛋白和全蛋白含量的变化。结果表明：冻结猪肉经静水解冻后,肌肉pH值接近6.0,解冻损失率和蒸煮损失率较低,静水解冻使猪肉的保水性维持较好。冻结猪肉解冻过程中肌浆蛋白和肌肉全蛋白浓度的变化对肉质构特性有显著或极显著影响。微波解冻有利于保持猪肉的嫩度和色泽,且通过微波解冻的冷冻猪肉其肌肉全蛋白含量较高,肉品的全质构特性较好。4 种解冻方法中,静水解冻和微波解冻能较好地保持解冻猪肉的品质。     

Separation and Characterization of a Porcine-specific Thermostable Muscle Protein from Cooked Pork

ABSTRACT: This study was undertaken to separate and characterize the porcine-specific thermostable muscle protein (psTSMP) recognized by monoclonal antibody, MAb 5H9, which was previously raised against crude porcine thermostable muscle proteins for detection of pork in cooked meats. The 24 kD antigenic components isolated from cooked pork by immunoaffinity chromatography consisted of a basic protein (pI = 9.4) and a group of isoelectric variants (pI ranging from 5.4 to 7.2). The basic protein was further isolated by methyl hydrophobic interaction and sulfonate ion-exchange chromatography. Immunoblot suggested the presence of this antigenic psTSMP in the tropo-nin fraction. Based on its molecular weight, pI, thermostability, and immunoreactivity, the psTSMP was tentatively identified as troponin I.     

Sodium Lactate/Sodium Tripolyphosphate Combination Effects on Aerobic Plate Counts, pH and Color of Fresh Pork Longissimus Muscle

The objective of this study was to evaluate the effects of sodium lactate/sodium tripolyphosphate pump combinations on the characteristics of pork loins. The product was manufactured to simulate fresh pumped pork loins currently available in the retail market. Paired fresh pork loins (longissimus muscle), pumped to contain 0, 1 or 2% sodium lactate (SL) and/or 0, 0·2 or 0·4% sodium tripolyphosphate (STP) were vacuum packaged and stored at 4°C for 28 days. In pork containing 0·4% STP, samples with 1 or 2% SL had lower pH values than those with 0% SL. Pork containing 1 or 2% SL generally had lower aerobic plate counts than those with 0% SL. Pork with 0·4% STP was darker (lower L* value) and redder (higher a* value) than that with 0 or 0·2% STP. When aerobic plate counts and color characteristics are used as the criteria, the optimum SL/STP combination for solutions used to pump fresh pork loins that are vacuum packaged and held under refrigeration was 1% SL with 0·2% STP.     

Denaturation Kinetics of Myofibrillar Proteins in Bovine Muscle

Differential scanning calorimetry was used to monitor the thermal denaturation kinetics of myofibrillar proteins in bovine muscle at pH 5.6. The activation energy, pre-exponential factor, rate constant and mean life time for each transition were calculated by means of a dynamic method. The kinetic values and the proposed reaction order (n= 1) were confirmed applying an isothermal method as a test. The position of the endothermal peaks proved to be pH dependent. Evidences suggest that peak III is a result of actin denaturation and possibly other thin filament proteins. Peaks I and II would represent the thermal transition of thick filaments. The number of bonds involved in each transition were estimated.     

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。     

不同冻结温度下牛肉的肌原纤维蛋白变性与肌肉持水性

为明确冷冻温度对牛肉肌原纤维蛋白变性和肌肉持水性（water-holding capacity,WHC）的影响、探讨肌 原纤维蛋白变性与WHC的相关性。以牛背最长肌作实验材料,探究－9、－18、－23、－38 ℃下冻结后肌原纤维 蛋白理化特性和牛肉WHC。通过测定巯基含量、蛋白质溶解度、Ca2＋-三磷酸腺苷酶（adenosine triphosphatase, ATPase）活力及蛋白质热稳定性考察牛肉冻结后肌原纤维蛋白变性情况,利用解冻汁液流失与加压失水率指标衡 量牛肉WHC,采用低场核磁共振（low field-nuclear magnetic resonance,LF-NMR）波谱和磁共振成像（magnetic resonance imaging,MRI）技术对比分析了肌肉水分分布情况,并于4 ℃解冻后测定了色差与剪切力。结果表明： －23 ℃与－38 ℃下冻结试样较－9 ℃与－18 ℃肌原纤维蛋白变性程度小：－23 ℃与－38 ℃下冻结试样蛋白质溶解 度、Ca2＋-ATPase活力、巯基含量和总变性焓相比－9 ℃与－18 ℃实验组较高（P＜0.05）。－23 ℃与－38 ℃下冻 结牛肉解冻后L*值、b*值、剪切力、解冻汁液流失和加压失水率显著低于－9 ℃与－18 ℃（P＜0.05）。LF-NMR 及MRI结果相互佐证了肉样在－23 ℃与－38 ℃冻结下肌肉WHC高于－9 ℃与－18 ℃的实验结果。肌原纤维蛋白理 化特性（蛋白质溶解度、Ca2＋-ATPase活力、巯基含量、总变性焓）与WHC（解冻汁液流失率、加压失水率）均呈 极显著相关（P＜0.01）,L*、b*值及剪切力亦与WHC存在极显著相关（P＜0.01）。相关性分析结果验证了牛肉冻结 过程中肌原纤维蛋白变性对肌肉持水性存在显著影响,进而导致牛肉解冻后出现肉色劣变、嫩度下降及汁液流失。