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.     

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。     

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.     

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.     

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.     

3种猪肉汤体系中蛋白质降解产物的比较研究

对3种不同烹制方法(水煮、炖煮和高压蒸煮)制得的猪肉和汤汁进行感官评定、总蛋白SDS-PAGE凝胶电泳以及总氮(TN)、水溶性氮(WSN)、非蛋白氮(NPN)和游离氨基酸(FAA)含量的比较研究。感官评定结果表明3种工艺分别为水煮30min,炖煮2h和高压蒸煮15min时,烹制所得肉和汤汁口感与风味最佳。总蛋白SDS-PAGE凝胶电泳图谱显示炖煮肉中大分子蛋白降解最为显著,炖煮肉汤中水溶性蛋白含量最高。水煮、炖煮和高压蒸煮使肉汤体系水溶性氮总量分别比鲜肉增加12%、24%和5%,非蛋白氮总量分别增加42%、59%和33%,游离氨基酸总量分别增加61%、78%和51%。炖煮猪肉的蛋白质降解程度比水煮和高压蒸煮高,且大部分蛋白质降解产物转移到汤汁中,赋予肉汤最优的营养和风味。     

Monoclonal Antibodies to Porcine Thermal-Stable Muscle Protein for Detection of Pork in Raw and Cooked Meats

Four hybridoma cell lines secreting monoclonal antibodies (MAbs) specific to porcine thermal-stable muscle proteins (TSMPs) were developed. The MAbs reacted with three protein bands (20.5, 22 and 24 kD) from raw pork extract; the protein band (24 kD) which was also present in cooked pork was identified as porcine-specific TSMP. Epitope analysis indicated four MAbs recognized same or closely located antigenic sites on the pork TSMP. The developed MAb-based indirect enzyme-linked immunosorbent assay (ELISA) enabled the detection of pork in raw and cooked heterogeneous meat mixtures as low as 10 g/kg. The curvilinear relations of second-degree polynomial (r² > 0.995) between pork concentrations and ELISA responses enabled quantifying degree of adulteration of pork in meat products.     

Effect of Pre-chill Removal of Kidney Fat on Young Angus Bull Carcass Quality and Longissimus Muscle Tenderness

The effect of pre-chill removal of kidney fat from bull carcasses on Longissimus palatability, histological and enzyme characteristics was studied. To better represent the time flow of product from packer to consumer, steaks were removed from one side of each carcass for evaluation after a 7-day chill. Carcasses having intact kidney fat exhibited firmer and more marbled Longissimus muscle, and this was reflected in slightly higher quality grades: low choice versus high select in carcasses having fat removed. No differences were observed in panel tenderness, shear force value, or histological and lysosomal enzyme characteristics. A slower pH decline was observed in muscle of carcasses with kidney fat removed.     

Electrical Stimulation Effects on Myoglobin Properties of Bovine Longissimus Muscle

Beef longissimus steaks from 40 bull carcasses were used to study the effects of electrical stimulation (ES) on meat color mechanisms and myoglobin properties. Total pigment concentration and ratios of myoglobin forms for ES and control (C) samples were not different. Color panel and several spectrophotometric measurements indicated ES produced a lighter, brighter-red color in displayed steaks. Disappearance of reduced myoglobin during blooming was similar in unaged C and ES steaks, but reduced myoglobin decreased faster during blooming of ES steaks aged 6 days. ES decreased anaerobic metmyoglobin reducing activity and induced more metmyoglobin formation when steaks were in a 1% oxygen atmosphere.     

不同加工工艺对预调理回锅肉的品质影响

该实验在传统回锅肉的加工基础上,围绕预调理回锅肉的3种不同工业化生产工艺,即油炸-高温灭菌、油炸-巴氏灭菌和炒制-巴氏灭菌,并以传统炒制的回锅肉作为对照组,研究加工工艺对回锅肉质构、色泽、TBARS值、过氧化值、可接受度的影响。结果表明,工业化的加工工艺制作的回锅肉感官品质低于传统方式制作的回锅肉,但是其脂肪氧化程度较低。油炸加工的回锅肉感官品质和脂肪氧化程度均好于炒制的回锅肉。     

Protein Denaturation and Starch Gelatinization in Hard-To-Cook Beans

A study was undertaken to assess protein denaturation and starch gelatinization in ground samples of common black beans exhibiting the hard-to-cook (HTC) defect. Using differential scanning calorimetry, no significant differences in either gelatinization or denaturation temperatures were found between hard and soft beans but tropical storage conditions produced significant increases in gelatinization enthalpy and decreases in denaturation enthalpy. Endotherms of cooked samples showed as little as 34% of the protein had denatured in HTC beans as compared to over 85% in soft beans. Micrographs indicated the ground raw material was composed of clumps of cotyledon cells; cooking soft beans produced cell separation but this did not occur in HTC samples. These data supported the idea that bean hardening was accompanied by limited water availability inside cotyledon cells that could reduce cell swelling, starch gelatinization and protein denaturation, leading to textural toughness.     

小麦籽粒蛋白质组分与面包烘焙品质性状关系的研究

利用３８个小麦种质材料,研究了小麦蛋白质组分与面包烘焙品质性状的关系。发现清蛋白或球蛋白与主要面包品质性状呈负相关,其中清蛋白含量与Ｚｅｌｅｎｙ沉降值呈显著负相关。醇溶蛋白或谷蛋白与面包品质性状呈正相关,谷蛋白与烘焙品质呈显著正相关。利用通径分析明确了不同蛋白组分对面包加工品质的直接作用和间接作用。据此提出改良面包加工品质及协调营养品质和面包加工品质的途径。     

蛋白质降解对猪肉制品品质影响的研究进展

蛋白质不仅是生命体最重要的且是除水分外含量最高的组成成分之一,也是食品主要的成分之一。在肉与肉制品中,蛋白质和氨基酸不仅是主要营养素,也是形成产品质构、风味和色泽的物质基础,并具有乳化、凝胶和稳定等多种功能作用。因此;肉与肉制品中蛋白质的降解会对产品品质有很大的影响。本文主要综述了猪肉蛋白质的主要种类、蛋白质降解伴随着的结构和组成的变化、蛋白质降解对猪肉制品品质的影响以及相关的分析测定研究进展,旨在为开展相关研究提供参考。     

Influence of Soy Protein and NaCl on the Rheological Properties of Beef, Pork or Chicken Muscle Homogenates

Yield stress, consistency index and flow behavior index of homogenates were 3.5–11.7 N/m², 6.9–14.9 N sⁿ/m², and 0.31–0.37, respectively, but with the addition of soy protein the respective values were 8.8–23.4 N/m², 15.7–34.7 N sⁿ/m², and 0.23–0.25. NaCl in the muscle homogenates changed yield stress, consistency index and flow behavior index to 17.6–26.4 N/m², 27.2–31.6 N sⁿ/m², and 0.23–0.25, respectively, but when both NaCl and soy protein were added, the respective values were 17.641 N sⁿ/m², and 0.24–0.29. Rheological parameters for homogenates containing soy protein decreased in value with NaCl addition but the magnitude of the decrease was lower when meats were present compared to the homogenate containing only soy proteins.     

Kinetic Compensation Effect in the Heat Denaturation of Whey Protein

The kinetic compensation effect in the heat denaturation of whey proteins was demonstrated using two different kinetic compensation relationships, i.e. Enthalpy (ΔH≠/Entropy (ΔS≠) compensation and Frequency Factor (In ko)/Activation Energy (E_a) compensation. Isokinetic temperatures determined by these methods were 84.0 and 87.8°C, respectively. These values were higher than those associated with thermal death of microorganisms caused by heat denaturation of proteins; however, they were in the experimental temperature range, correlating well the dependent relationship between kinetic parameters.