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.     

Variations in Rate of Water Loss as Related to Different Types of Post-rigor Porcine Musculature During Storage

The changes in percent drip loss (PDL), total water content, and shrinkage at different postmortem (PM) stages were examined in four pork quality classes: pale, soft, exudative (PSE); reddish-pink, soft, exudative (RSE); reddish-pink, firm, non-exudative (RFN); and dark, firm, dry (DFD). The PDL of PSE and RSE samples rapidly decreased with time, whereas those of RFN and DFD did not. Although the PDL of RSE showed a decrease (p < 0.05) with time, the percentage of total water did not change. Large pieces of loin exhibited less shrink than smaller pieces. These results indicated that water-holding capacity, as expressed by shrinkage, improved at extended PM times.     

Protein Denaturation in Pork Longissimus Muscle of Different Quality Groups

Differential scanning calorimetry (DSC) was used to investigate the protein denaturation characteristics of pork muscles from four quality groups namely RFN (red, firm, and non-exudative), RSE (red, soft, and exudative), PFN (pale, firm, and non-exudative), and PSE (pale, soft, and exudative). The thermograms indicated three endothermic peaks between 45°C to 90°C, corresponding to denaturation of myosin (peak I), sarcoplasmic proteins (peak II), and actin (peak III). The myosin peak was much reduced in PSE samples, while the actin peak remained almost identical in all groups. RFN and RSE samples were found to have very similar protein denaturation characteristics and were not significantly different in their thermodynamic protein denaturation parameters. PFN samples showed similar myofibrilar protein denaturation but significantly different sarcoplasmic protein denaturation characteristics compared to normal (RFN) samples according to their DSC thermograms. Based on these findings, it was suggested that the pale color in PFN pork is linked to sarcoplasmic protein denaturation.     

Use of electrical conductivity to predict water-holding capacity in post-rigor pork

This study was designed to re-examine the interrelationships among ultimate pH (pH_u), electrical conductivity (EC) and water-holding capacity (WHC), and to test if EC, using one of two EC instruments, and pH_u can be used to predict WHC. The % drip (PD) was used as measure of WHC. Forty-seven pork loins were classified either as PSE (pale, soft, exudative), RSE (reddish-pink, soft, exudative), RFN (reddish-pink, firm, non-exudative) or DFD (dark, firm, dry), based on L* values, PD and pH_u. The measurement of EC, conducted using the instrument developed at the University of Wisconsin-Madison (UW-EC) was highly correlated to PD at 24 h post mortem (CD=66%), but the pH (NWK) measure of EC was not as highly related to WHC as UW-EC. The predictive value of pH_u and EC for WHC were similar. When 47 samples were divided into three different groups, such as low (< 2% drip), medium (2–6% drip) and high (> 6% drip) drip loss, UW-EC alone grouped 80% of the samples correctly. Thus, EC seemed to be an accurate predictor of WHC in pork muscle when measured at 24 h post mortem. It is conceivable that EC can be used independently, or with even better success in combination with pH_u, to classify WHC of pork carcasses.     

Sensory characteristics of cooked pork loin as affected by nucleotide content and post-mortem meat quality

Muscle longissimus dorsi excised at 2hr post mortem was utilised to study the effect of post-mortem meat quality, and their content of nucleotide metabolites, on the sensory characteristics of cooked loin. Four different post mortem meat qualities were defined: pale soft exudative (PSE), red soft exudative (RSE), red firm non-exudative (RFN) and dark firm dry (DFD). The DFD meat quality class showed low sour and salty tastes and a high sweet taste, low astringency and high juiciness and tenderness, giving the best overall quality. On the other hand, the RSE quality class produced a meat with a low juiciness and high hardness, and a low overall quality although these differences were not significant (p<0.05) against RFN and PSE meats. The effect of nucleotide metabolite contents on the sensory meat properties were most significant on taste although, the different meat qualities were only significantly different (p<0.05) in the content of hypoxanthine, guanosine, GDP and IDP.     

磷酸盐对PSE 猪肉肌原纤维蛋白溶胶及凝胶性质的影响

PSE 肉的肌原纤维蛋白质(MP)的溶解度比正常肉(red, firm and non-exudative;RFN)低、凝胶性质比RFN差,本研究探讨磷酸盐对PSE 猪肉凝胶特性的影响。以猪背最长肌PSE 和RFN 肉为材料,采用分光光度法、质构测定法等研究六偏磷酸钠(SHMP)、焦磷酸钠(SPP)、三聚磷酸钠(TPP)对MP 溶解特性、聚集性以及凝胶强度的影响。结果表明,磷酸盐对PSE 和RFN 提取MP 的溶解度、蛋白质聚集性和凝胶强度均有显著的影响,TPP 添加量为0.25% 时PSE 的凝胶强度接近未添加TPP 的RFN 的凝胶强度。磷酸盐可改善体系环境,改善PSE 蛋白质溶胶及凝胶的功能特性。     

Use of visible spectroscopy to assess colour development during ageing of fresh pork from different quality classes

The objective of this research was to study the entire visible spectra evolution during meat ageing in different pork meat quality classes (PSE, DFD and RFN). The potential use of the visible spectra for discriminating low meat quality classes during the 24 hours postmortem (hpm) was also analysed. For these purposes, 26 pork loins were used: 3 PSE (pale, soft and exudative), 3 DFD (dark, firm and dry) and 20 RFN (red, firm and non‐exudative). At 12, 24, 48 h and 7 days postmortem, reflectance spectra (400–700 nm) were obtained by a spectrocolorimeter Minolta CM‐3600D after one and a half hour of blooming time. It was demonstrated that the ageing time has an influence in colour parameters and in blooming ability of RFN loins. The evolution of visible spectra was influenced by ageing time in PSE and RFN loins, while the visible spectra of DFD loins showed no variation with postmortem time. The results showed the possibility of separating PSE meats from the other classes by using visible reflectance spectra at 24 hpm.     

Pork meat quality affects peptide and amino acid profiles during the ageing process

Twenty pork carcasses were classified in different pork meat qualities: red, firm and non-exudative (RFN), pale, soft and exudative (PSE), red, soft and exudative (RSE) and dark, firm and dry (DFD) meat. The content of peptides and free amino acids during the ageing process was analysed and compared within quality classes. Four peptide fractions were isolated through cation-exchange and reverse-phase chromatography. The main significant differences among qualities were obtained for peptide fractions 3 and 4. Peptide fraction 3 at 4 days and peptide fraction 4 at 2 h postmortem were higher in the ideal pork quality (RFN) than in the other quality classes. The ageing of pork meats produced a general increase in all free amino acid concentrations for the studied quality classes except for Gln, β-Ala, Taurine and Orn and the dipeptides carnosine and anserine. The DFD class showed higher increases in Lys, Ala and Met probably due to the activation of neutral aminopeptidases.     

Shelf life of pork from five different quality classes

A total of 117 loins were selected on the cutting line at 24 h post-mortem to study the long term shelf life (35 days, 4 °C) of vacuum packaged pork from five different quality classes (PSE: pale, soft, exudative; PFN: pale, firm, non-exudative; RSE: red, soft, exudative; RFN: red, firm, non-exudative; and DFD: dark, firm, dry). The microbial load at 0 d was not significantly different (P > 0.05) among the pork quality classes, indicating that the initial microflora was influenced by the dressing conditions at the plant, not by the meat quality class. But after 35 d of storage, total aerobic mesophilic and presumptive lactic acid bacteria counts were higher (P < 0.05) in DFD pork due to its higher ultimate pH. RSE was the second quality class most susceptible to spoilage, whereas PFN, RFN and PSE pork had similar microbial loads. Further research is needed to elucidate the causes of the shorter shelf life in RSE pork.     

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 use of muscle protein solubility measurements to assess pig lean meat quality

The relationships between sarcoplasmic, myofibrillar and total soluble protein (sarcoplasmic + myofibrillar) concentrations, and subjective (colour-structure score) and objective (drip loss and reflectance) measures of lean meat quality were determined using 100 samples of M. Longissimus dorsi that showed a wide range of quality. There was good agreement between the subjective and objective assessments of quality. Overall, the concentration of soluble sarcoplasmic proteins showed the highest correlations with quality assessments. The relationships with total soluble protein were poorer and were least good with myofibrillar protein concentration. Sarcoplasmic protein concentration was also the best potential predictor of meat quality when pale, soft, exudative (PSE) muscles were excluded from the sample. However, if dark, firm, dry (DFD) muscles were excluded instead, the concentration of total soluble protein was as good as, or better than, sarcoplasmic protein as a potential predictor of quality, particularly muscle reflectance.     

THE RELATIONSHIP BETWEEN COLOR AND WATER-HOLDING CAPACITY IN POSTRIGOR PORCINE LONGISSIMUS MUSCLE

A total 264 pork loins were selected to represent a wide range of pork quality of the longissimus thoracis et lumborum. CIE L*C*h color space showed a closer relationship to the subjective color score than L*a*b*color space. Lightness (L*) was the best measure to predict water-holding capacity (WHC). There were highly significant (p < 0.001) correlations between the measures of color and WHC, and curvilinear relationships between either WHC and color or pHu were observed. In normal muscle color range (reddish-pink), there was considerable variation in WHC. Within the RSE + RFN groups of muscles, less variation of WHC could be accounted for by variations in color measurements. Color and WHC were not closely related and suggest that the RSE (reddish-pink, soft, exudative) condition should be classified as a separate quality category of pork muscle.     

Postmortem meat quality and sex affect textural properties and protein breakdown of dry-cured ham

Texture measurements by instrumental texture profile analysis (TPA) and protein degradation analysis by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) were performed on 30 dry-cured hams resulting from four different post-mortem meat qualities categories (PSE, RSE, RFN and DFD). The main differences were observed in dry-cured hams from PSE and RFN meat qualities. Penetration force (80%), hardness, springiness, cohesiveness and chewiness, were significantly lower (P<0.05) in PSE than in RFN quality classes. The rate of the ripening process was affected as a higher proteolysis and absence of fragments at 150 and 85 KDa in PSE in relation to RFN classes, and with an intermediate proteolysis of RSE and DFD classes. The effect of sex was observed as a significant (P<0.05) low hardness in the hams obtained from female pigs. The duration of the ripening, for a better uniformity in dry-cured ham production, should be adapted to the initial pH and to drip loss parameters of the raw material.     

Water Extractable Proteins of Porcine Muscle

SUMMARY: The study was performed on 31 samples of porcine muscle (m. longissimus dorsi) of different qualities, ranging from extremely pale, soft and exudative (PSE) to dark red in color, firm in structure and dry in appearance (DFD) in order to determine the water solubility of muscle proteins 24 hr post mortem. It was found that the water solubility of muscle proteins depends on the quality of the muscle, and is lowest in extremely PSE muscle. It was demonstrated, with the aid of electrophoresis on agar and acrylamide gels, that some sarcoplasmic proteins which undergo precipitation 30 min after adding a citrate-phosphate buffer (pH 4.6) at temperature of 20°C are extracted in smaller amounts from PSE muscle than from normal muscle. One of these fractions was benzidine positive.     

Centrifugal drip is an accessible source for protein indicators of pork ageing and water-holding capacity

Achieving an improvement in water-holding capacity (WHC) of pork and a reduction in the incidence of pale, soft and exudative (PSE)- and dark, firm and dry (DFD)-like meat is a major challenge for the swine industry. Using proteomics, we sought to identify proteins associated with WHC and to monitor postmortem protein degradation. Twenty longissimus samples were categorised into WHC phenotypes. The centrifugal drip was subjected to SDS-PAGE and mass-spectrometry. Forty-four proteins were identified in the centrifugal drip proteome. Changes occurred in volume of five bands across the ageing period, with most significant changes representing increases between day 3 and day 7. Seven proteins were identified in these bands, most with functions in glycolysis. One band significantly differed in abundance across WHC phenotypes. Peptide signatures of the heat shock protein family were identified in this band.     

Identification and characterization of pigs prone to producing 'RSE' (reddish-pink, soft and exudative) meat in normal pigs

RSE (reddish-pink, soft and exudative) meat was investigated using pigs of three different halothane genotypes. A significantly lower pH_1h, value was observed in RSE compared with that of RFN (red, firm and non-exudative) -meat, both of which have values higher than 6.0 at 1 hr post-mortem. Drip loss (%) in RSE-meat was ≥7%, which was twice that of RFN-meat. Normal values for fibre optic probe and Minolta L and a were observed for RSE-meat. RSE-meat could be derived from NN and Nn pigs, and its formation could be induced from RFN-prone pigs by poor post-slaughter management. Pigs expected to produce RSE-meat were identified using small biopsy samples of M. longissimus dorsi (LD). Predicted RSE-meat in live pigs was confirmed by post-mortem assessments of meat quality using LD muscle. With NN Landrace-Yorkshire × Duroc pigs, 15.6% were identified to be RSE-prone in live pigs, and a further 6.7% RSE was induced after slaughter from RFN pigs. The rate of glycolysis determined from biopsy LD samples and at 1 hr post-mortem (pH_1h) were significantly (p < 0.001) faster in RSE than in RFN-prone pigs, but significantly slower than those of PSE-prone pigs. Good correlations (p < 0.001) were observed between biopsy fluid (F) values, an indicator of water-holding capacity (WHC), and drip loss (r = 0.652) from post-mortem LD muscle, and between biopsy pH (F), an indicator for the rate of glycolysis, and F (r = −0.828). These results show that the skeletal muscle test using biopsy LD muscle could be employed to reduce the incidence of RSE-meat.     

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。     

Changes in solubility and enzymic activity of muscle glycogen phosphorylase in PSE-muscles

Comparison of the crude extracts of soluble proteins of PSE (pale, soft and exudative) and normal porcine muscles shows that the solubility and activity of muscle glycogen phosphorylase are diminished in PSE muscles. In the insoluble fractions of the muscle extract, however, an increased amount of a protein with the molecular weight of the phosphorylase subunit (92·500-95·000) can be found by means of SDS-electrophoresis. The PSE conditions with high temperatures of 36-40°C in the first hour post mortem and a low pH of 5·3-5·8 at the same time post mortem are simulated with normal porcine muscles at twenty-four hours post mortem which causes the same change in solubility and activity of muscle glycogen phosphorylase as in PSE muscles. This proves, for the first time, that low pH and high temperature in whole muscles cause a denaturation of phosphorylase, as indicated by both reduced activity and decreased solubility. Previous studies have looked only at one of these aspects. This supports the hypothesis of Bendall & Wismer-Pedersen (1962) that in PSE muscles a partial denaturation of sarcoplasmic protein occurs.     

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。     

Consumer-rated Quality Characteristics as Related to Purchase Intent of Fresh Pork

Consumers (n=556) rated pink color, wet/dry appearance, overall acceptability and purchase intent of normal, pale, soft and exudative (PSE), and dark, firm and dry (DFD) pork loin slices in PVC packages in five retail supermarkets. DFD samples appeared driest and PSE samples appeared wettest. Samples in the higher ranked two purchase intent categories appeared more wet than those in the lower three categories. The pinker PSE samples and all DFD samples were in the higher ranked purchase intent categories. Purchase intent generally paralleled overall acceptability; however, prediction equations indicated that wet/dry appearance, color and overall acceptability all contributed to purchase intent decision depending on muscle condition.