PSE肉中乳酸含量变化分析

利用冷冻离心和硫代巴比土酸(TBA)比色法检测正常肉、PSE肉中乳酸含量的变化.结果显示,乳酸的回收率为96.95%～103.26%.在0h,RFN肉和PSE肉中乳酸的平均含量分别为0.0594mg/g和0.1350mg/g;PSE肉中乳酸含量2h后上升到1.0708mg/g,RFN肉中乳酸含量在72h后上升到1.0260mg/g.     

失色水化松软肉(PSE)和深色坚实干燥肉(DFD)的快速检定法

<正>对猪肉和牛肉的大量研究表明在死后几分钟内可以将失色水化松软肉(PSE)和深色坚实干燥肉(DFD)同正常的肉区分开,这是因为它们缺乏象糖原和三磷酸腺苷那样能量丰富的物质。PSE和DFD肉只含     

皮质醇激素和血液生化指标变化对猪肉劣质肉的指示作用

为寻找猪肉劣质肉的指示指标,比较了不同质量猪肉对应皮质醇激素和血液生化指标的变化。结果表明,劣质肉中白肌肉(PSE)对应生猪血糖浓度显著高于正常肉(RFN)(P<0.05),劣质肉中黑干肉(DFD)对应生猪皮质醇浓度显著高于RFN肉(P<0.05)。说明血糖可作为劣质肉中PSE肉的重要指示指标,当宰前血糖浓度达到(17.21±3.12)mol/L时,可能产PSE肉;皮质醇可作为劣质肉中DFD肉的重要指示指标,当宰前皮质醇浓度达到(512.70±49.9)nmol/L时,可能产生DFD肉。     

识别PSE肉与DFD肉的“慧眼”

众所周知,影响肉品品质的因素有很多,如肌内脂肪、肌肉嫩度、异常肉质等。其中典型的异常肉质就是PSE肉（肉色灰白、肉质柔软、表面潮湿或有水分渗出）和DFD肉（肉色黑、肉质硬、表面发干）。PSE肉由于水分流失,胴体产量会下降,而且猪肉制熟后较干,会影响食用时的口感。DFD肉口味较差,并且由于pH值偏高,利于微生物繁殖,因而腐败变质几率较高,     

黑切牛肉贮藏过程中活性氧相对含量变化及其与肉品质指标相关性分析

活性氧在宰后肉品质形成过程中起重要作用，研究活性氧在黑切(dark, firm and dry,DFD)牛肉中对肉品质变化的影响。以黑切牛肉(pH_{24 h}>6.2)为研究对象，取宰后4℃排酸24 h牛肉，4℃贮藏，在贮藏1、24、72、120 h分别测定活性氧相对含量、色差值、pH值、蒸煮损失率、滴水损失率、羰基含量及巯基含量，并进行相关性分析。结果表明：贮藏期间黑切牛肉的pH值大于6.5，显著高于正常牛肉；活性氧相对含量在贮藏期间呈升高趋势，一直高于60 L/(min·mg)，贮藏72、120 h高于正常牛肉；红度值在贮藏期间均在4.47以下，低于正常牛肉；滴水损失率低于8.90%，蒸煮损失率低于28.10%，均低于正常牛肉；羰基含量高于2.80 nmol/mg、巯基含量高于37.16 nmol/mg，羰基含量在贮藏72、120 h高于正常牛肉，巯基含量贮藏期间低于正常牛肉；相关性分析表明，黑切牛肉中活性氧与肌肉蛋白质氧化指标羰基含量、巯基含量显著相关。活性氧与黑切牛肉成熟过程中肉品质形成密切相关，其可能是调控黑切牛肉品质变化的重要因子。     

鸡肉类PSE肉与正常肉流变、质构特性的比较

以亮度值(L*)与屠宰24h后的pH值(pH24h)作为区分类PSE肉与正常鸡肉的指标,对两者肉糜的流变特性、质构特性和蒸煮损失进行研究。结果表明:具有低pH24h、高L*值的类PSE肉,在流变性、蒸煮损失和质构上存在显著差异。类PSE肉的流变曲线趋势异于正常肉,表现出低的贮能模量和大相位角正切值(P<0.05),极值所对应的温度低于正常肉(P<0.05);类PSE的蒸煮损失高于正常肉(P<0.05),硬度、弹性、黏聚性、咀嚼性和回弹力显著低于正常肉。鸡胸肉的pH值和L*值与其肉糜的质构与流变特性密切相关,是分析和控制类PSE对深加工产品影响的重要参考因素。     

猪PSE肉与正常肉的肌原纤维形态学比较研究

通过肌原纤维的形态学、易碎度和肌节长度的测定,对猪PSE肉和正常肉肌原纤维的易碎性进行了比较研究,发现肌原纤维的肌节断裂发生在肌节的明带(I带),随着匀浆时间和5℃贮存时间的延长,易碎度也随之增加,PSE肉在前2天的碎化幅度较大,而正常肉在2～4d的碎化幅度较明显。PSE肉与正常肉的肌原纤维易碎度变化规律一致,温度对肌原纤维的碎化效应大于时间效应,且正常肉肌原纤维断裂对温度的敏感性大于PSE肉。由于PSE肉部分肌球蛋白变性,其肌原纤维的舒展肌节长度总是小于正常肉。     

关于PSE肉的研究(综述)

<正> 长期以来,肉类生产和肉类市场上最大的肉品质量问题就是异常肉的出现,即PSE肉(Pale soft Exudative)和DFD肉(DarkFirm Dry).这两种肉都表现为外观色泽差,风味不浓,鲜肉和加工制品不受消费者欢迎,在肉类市场上缺乏竞争力,销售价格低于正常肉.据统计,这两种肉的发生率近年来有不断上升的趋势.DFD肉的发生率可超过30%,而PSE肉的发生率也可达到24%以上.目前,在我国,这两种肉的发生率均在10%左右.两种异常肉的发生率不断地上升,这不仅使肉类生产者蒙受巨大的经济损失,同时也给肉类加工业和消费者带来许多麻烦.因此,许多国家都十分重视这     

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。     

猪PSE肉与正常肉肌原纤维蛋白质抽提率和持水性的比较研究

对猪PSE肉与正常肉的肌原纤维蛋白质抽提率、总-SH基和持水性进行了比较研究。通过肌肉蛋白质在不同离子强度溶液中的抽提、0℃贮藏不同时间对肌原纤维蛋白质抽提率、-SH基和持水性的变化的测定,结果表明:PSE肉肌原纤维蛋白质的抽提率、-SH基和持水力都比正常肉低。PSE肉与正常肉间的肌浆蛋白变性差异不明显。由于肌肉的僵硬期的影响,肌原纤维蛋白质持水力与其变性程度要在解硬后(0℃,6～7d)才体现出较好的相关性。肌原纤维蛋白质抽提率可作为鉴别PSE肉与正常肉的重要指标。     

Lipid Oxidation, Color, Volatiles, and Sensory Characteristics of Aerobically Packaged and Irradiated Pork with Different Ultimate pH

ABSTRACT: Irradiation and storage increased lipid oxidation of normal and pale-soft-exudative (PSE) muscles, whereas dark-firm-dry (DFD) muscle was very stable and resistant to oxidative changes. Irradiation increased redness regardless of pork-quality type, and the increases were proportional to irradiation dose. Irradiation increased the production of sulfur-containing volatiles, but not lipid oxidation products. The total volatiles produced in normal and PSE pork were higher than the DFD pork. Some volatiles produced in meat by irradiation evaporated during storage under aerobic packaging conditions. Nonirradiated normal and DFD pork had higher odor preference scores than the nonirradiated PSE, but irradiation reduced the preference scores of all 3 pork-quality types.     

Effects of pork muscle quality on bacterial growth and retail case life

The effects of muscle quality (PSE, normal, DFD) upon the bacteriology and retail case life of pork chops were determined. Pork loin chops were processed from boneless backs after 90 days of frozen storage at -30°C. Variation in bacterial numbers was due to a highly significant (p < 0·001) storage time by muscle quality interaction. During simulated retail display, total psychrotrophs, Pseudomonas spp., Brochothrix thermosphacta and Enterobacteriaceae were lowest on PSE pork and highest on DFD pork in comparison to normal pork. Differences in bacterial densities were due to a longer lag phase in PSE pork and a shorter lag phase in DFD pork than in normal pork. Of the three muscle quality groups, DFD was most susceptible to the development of spoilage odours, while PSE pork was most sensitive to deterioration in appearance.     

Discoloration of Fresh Pork as Related to Muscle and Display Conditions

Pale, soft, exudative (PSE), normal, and dark, firm, dry (DFD) pork was held 7 days at 4°C under light or dark then color was evaluated instrumentally and visually. Change in reflectance (R630-R580) was used to estimate color changes due to oxymyoglobin. PSE pork was lighter (high L*) than normal and DFD pork, but did not change over time. An increase in a* and R630-R580 occurred the first day for normal and DFD, but not for PSE samples. A subsequent increase in hue angle and decrease in R630-R580 (loss of redness) occurred in PSE and normal, but not in DFD samples. Changes in hue angle and R630-R580 were more rapid in PSE than in normal samples. Light exposure accelerated all changes except L*. Visual redness inversely correlated with L* value.     

PSE(白肌)、RFN(正常)、DFD(黑干)3种质量猪肉冷藏期间的肉色稳定性

比较了PSE(白肌)、RFN(正常)、DFD(黑干)3种质量猪肉冷藏期间的肉色稳定性。宰后24h直接切块取样的3种质量猪肉(背最长肌)于(2±1)℃下避光透氧包装[O2透过率=2.06×10-3mL/(m2.h.Pa)]冷藏6d,采用色度计法测定了样品表面L*(亮度)值、a*(红色度)值、b*(黄色度)值、hueangle(色调角)值。从上述指标的变化研究了3种质量猪肉表面的肉色稳定性。3种质量猪肉表面肉色稳定性顺序为:DFD>RFN>PSE;a*值下降、hueangle值上升可反映肉色稳定性变差。     

CONSUMER EVALUATION OF PORK APPEARANCE WITH DIFFERING PHYSIOLOGICAL AND PACKAGING CONDITIONS

Consumers (n = 116) evaluated color (pink intensity), appearance (wet/dry), overall acceptability and purchase intent of normal, PSE and DFD pork loin slices in PVC and in vacuum packages. Packaging x muscle condition affected (p < 0.05) appearance, overall acceptability and consumer purchase intent of pork slices. Color differences were perceptible to consumers between packaging treatments. PVC-packaged pork was pinker than vacuum-packaged pork. Vacuum-packaged, PSE pork appeared drier than PVC-packaged PSE pork. Normal pork was more acceptable than PSE pork regardless of packaging. DFD pork acceptability was not different from that of normal pork when vacuum packaged. In general purchase intent paralleled consumer evaluation of overall acceptability. Instrumental color data and pH for samples evaluated are also presented.     

EFFECTS OF INJECTION OF A DILUTE PHOSPHATE-SALT SOLUTION ON PORK CHARACTERISTICS FROM PSE, NORMAL AND DFD CARCASSES

Phosphate-salt pump effects were evaluated on sensory characteristics of pale, soft, exudative (PSE) pork, normal and dark, firm and dry (DFD) pork. Water-holding capacity, instrumental color (L*, a*, b*), pH, and muscle color scores were determined at 24 h postmortem on pork loin pairs (n=21 pairs). Based on color score, paired loins were assigned to PSE, normal or dark, firm, dry groups. PSE muscles were lighter, redder and more yellow than normal or DFD muscles; hue angle indicated that DFD muscles were actually closer to the true red axis of the CIE Lab Color Space. Drip and purge losses were higher (p<0.05) in PSE muscles. Paired loins were pumped with water (controls) or 0.3% tripolyphosphate solution (0.25% salt) to 110% of original weight, vacuum packaged, frozen, cut into chops, and cooked to 70 or 80C. Phosphate-salt pumped loins were juicier and more tender (p<0.05) than water-pumped loins regardless of muscle condition. Loins cooked to 70C were juicier, were more tender (sensory) but required more force to shear than those cooked to 80C.     

Effects of Endpoint Temperature on the Internal Color of Pork Loin Chops of Different Quality

ABSTRACT: The effects of 5 endpoint temperatures for cooked, internal color were determined for boneless pork longissimus muscle from 4 treatment groups: normal, normal-injected, PSE, and DFD. Visual and instrumental color, myoglobin denaturation, and acid phosphatase (ACP) of raw and cooked samples were evaluated. Visual internal color became (P < 0.05) less pink as endpoint temperature increased; however, DFD chops were more pink (P < 0.05) and PSE chops were less pink (P < 0.05) than other treatments at most endpoint temperatures. Cooked color was similar (P > 0.05) for chops from normal and normal-injected groups. Myoglobin denaturation increased as endpoint temperature increased. ACP activity in raw chops was not affected by treatment group and it was a good indicator of doneness at 71.1 °C.     

Metmyoglobin Reducing Capacity of Fresh Normal, PSE, and DFD Pork During Retail Display

Fresh pale, soft, exudative (PSE), dark, firm, dry (DFD), and normal pork were stored under light or dark conditions at 4°C for 7 days. Sample pH, metmyoglobin reductase activity, oxygen consumption rate, and relative surface metmyoglobin and oxymyoglobin contents were determined. DFD pork had the highest metmyoglobin reductase activity and oxygen consumption rate. Enzyme activity of PSE was lower than that of normal pork, but no difference existed in oxygen consumption rate between PSE and normal samples. Metmyoglobin reductase activity dropped slowly during meat storage; oxygen consumption rate sharply decreased during the first day of storage. Both metmyoglobin reductase activity and oxygen consumption rate declined more rapidly in the light. Results can help develop guidelines for display and packaging of pork.     

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。