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.     

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.     

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.     

Evolution of hydrophobic polypeptides during the ageing of exudative and non-exudative pork meat

Thirty-six carcasses from 6-month-old pigs were classified in different exudative groups based on measurements of pH_2h, pH_24h, the colour parameter L^* and drip loss. A fraction containing polypeptides between 66 and 21 kDa was analysed by reverse phase chromatography at 2-h post-mortem and the evolution of 8 polypeptide fractions followed during ageing and related to meat quality. Three polypeptide (fractions P2, P3 and P4) at 2-h post-mortem showed significant lowest area values in the dark firm and dry class. During ageing, the higher content of P4 in exudative meats at 8-h post-mortem could be due to activation of the cathepsin system. On the other hand, P3 and P4 increased in DFD meats during the first 96-h post-mortem probably due to higher calpain activity. Few differences in polypeptides were related to meat qualities although they are important as precursors of small peptides and free amino acids.     

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.     

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).     

Optimization of Muscle Enzyme Colorimetric Tests for Rapid Detection of Exudative Pork Meats

The assays of muscle arginyl (RAP) and alanyl (AAP) aminopeptidases and dipeptidyl peptidase IV (DPPIV) have been optimised using colorimetric (aminoacyl-p-nitroanilide) substrates in order to design an appropriate test in their assay in fresh pork meat. Kinetic parameters, Km and Vmax, were calculated for the three enzymes using pNa substrates. The rapid colorimetric analysis was developed and applied directly on the muscle extracts from 16 samples previously classified in different pork meat qualities. The exudative meat quality class (PSE) showed significant lower values for these enzyme activities than the ideal meat quality (RFN) and the dark, firm and dry (DFD) quality classes. The protocols can be easily transferred to food industry because the use of colorimetric substrates and a microplate colour reader are feasible to use in large-scale production systems.     

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.     

Dielectric Properties of Pork Muscle

Dielectric properties were measured across a frequency range from 200 MHz to 20 GHz and temperature range from 25 to 85°C for pork meat samples (grouped in four different quality classes). Dielectric properties varied widely with frequency and the loss tangents of different meat quality classes followed different trends. Discriminant analysis indicated that 2400 MHz was most significant (P < 0.05) for separation of the different classes. There were significant changes (P < 0.05) in the dielectric properties within the range of the temperatures corresponding to protein denaturation temperatures. There was clear segregation between the firm and non-exudative (red, firm, and non-exudative; pale, firm, and non-exudative) and the soft and exudative (red, soft, and exudative; pale, soft and exudative) samples. The results showed that dielectric properties could be useful in meat quality classifications.     

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。     

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.     

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.     

Low-frequency dielectric spectrum to determine pork meat quality

The use of dielectric spectra to determine meat quality classes (PSE, DFD, RFN) in porcine muscle during postmortem period was evaluated. The changes in dielectric properties during meat ageing were also analyzed for each meat quality class. For these purposes, dielectric spectra were measured from 100 Hz to 0.4 MHz in parallel and in perpendicular to muscle fiber directions. Significant differences (p < 0.05) in dielectric constant and loss factor among classes were observed at 24 and 48 h post-mortem. Thus, the use of dielectric properties to detect low meat qualities is more reliable at 24 h after slaughtering. Moreover, two indexes for evaluating meat ageing were developed from dielectric properties with good results. This research is the first step for developing a sensor based on electromagnetic waves at radio frequencies for controlling pork meat quality. The results are promising and some definite frequencies are demonstrated to be useful for these purposes.Industrial RelevanceThe results of this research article are demonstrated to be useful for discriminating low meat qualities (PSE and DFD meats). Thus, the industrial relevance is clear in this case because the detection of low meat qualities is identified as one of the most important challenges of meat industry nowadays. On the other hand, basing on the results of the present paper it is possible to develop a prototype for industrial applications. Moreover, two possible Indexes are developed in the present paper for determining meat freshness which also can be considered important from an industrial point of view. All this determinations were made by using dielectric spectroscopy which can be considered an emerging technology. For all these reasons we are sending to this journal “Innovative Food Science and Emerging Technologies” our results.     

Utilization of response surface modeling to evaluate the effects of non-meat adjuncts and combinations of PSE and RFN pork on water holding capacity and cooked color in the production of boneless cured pork

Boneless cured pork was produced from combinations of pale, soft, and exudative (PSE) and red, firm, and non-exudative (RFN) semimembranosus muscle. Response Surface Methodology was utilized to determine the effects of soy protein concentrate (SPC), sodium caseinate (SC), and modified food starch (MFS) on the water holding capacity and cooked color in a chunked and formed product. Fifteen ingredient combinations were replicated three times for each PSE and RFN combination giving 75 treatments per replication. Utilization of SPC decreased (P<0.01) cooking loss and redness while increasing (P<0.01) yellowness. MFS decreased (P<0.01) expressible moisture, and both MFS and SC increased (P<0.05) cooked redness while decreasing (P<0.01) cooked lightness. Product formulations using these adjuncts demonstrate potential to improve the water-holding capacity and cooked color in PSE as well as RFN pork. This research also demonstrated that diluting RFN pork with no more than 25% PSE pork permits the formation of a high quality boneless deli ham roll.     

Microwave dielectric spectroscopy for the determination of pork meat quality

The use of dielectric spectra to detect quality defects in porcine muscle during postmortem period was evaluated. The changes in dielectric spectra during meat ageing were also studied. For these purposes, dielectric spectra were measured by using an Agilent 85070E Open-ended Coaxial Probe connected to an Agilent E8362B Vector Network Analyzer from 500 MHz to 20 GHz parallel and perpendicular to muscle fiber direction. This study reveals that dielectric properties at two punctual frequencies (0.5 GHz and 10 GHz) are a useful tool to determine meat quality classes (RFN, PSE, and DFD) soon (6 h) after slaughter. Based on these results, it is possible to develop control algorithms in order to discriminate low quality pork meats and to decide their best uses. Moreover, the evolution of dielectric spectra during meat ageing showed important variations only in DFD meats, while in PSE and RFN meats the variations were observed only at some punctual frequencies of the spectrum during the 24 h after slaughter.     

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。     

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.     

Effect of ionizing radiation on quality characteristics of vacuum-packaged normal,pale–soft–exudative,and dark–firm–dry pork

Normal, pale–soft–exudative (PSE), and dark–firm–dry (DFD) pork Longissimus dorsi muscles were vacuum-packaged, irradiated at 0, 2.5 or 4.5 kGy, and stored at 4 °C for 10 days. The pH, color and lipid oxidation of pork were determined at 0, 5 and 10 days of storage. Volatile production from pork loins was determined at Day 0 and Day 10, and sensory characteristics at Day 7 of storage. Irradiation increased the redness of vacuum-packaged normal, PSE and DFD pork. However, the 2-thiobarbituric acid reactive substances (TBARS) values of three types of pork were not influenced by irradiation and storage time. Irradiation increased the production of sulfur (S)-containing volatile compounds, such as mercaptomethane, dimethyl sulfide, carbon disulfide, methyl thioacetate, and dimethyl disulfide, as well as total volatiles in all three types of pork. Normal pork produced higher levels of total and S-containing volatile compounds than the PSE and DFD pork did. The volatiles produced by irradiation were retained in the vacuum packaging bag during storage. Although the odor preference for the three meat types of pork was not different, the panelists could distinguish irradiated meat from the non-irradiated. Industrial relevance: Several US meat companies have already started test-marketing irradiated meat products. Irradiation and the subsequent storage of pork improved the color of PSE and DFD pork, and showed generally similar effects on the production of volatiles, except that there appeared to be a lower level of S-volatiles in the PSE than in the other two samples. This indicated that irradiation can increase the utilization of low-quality pork (PSE and DFD). DFD pork, in particular, which has shorter shelf-life than the others, could benefit the most from irradiation because the shelf-life of DFD meat can be extended significantly by both the methods of vacuum packaging and irradiation.     

UTILIZATION OF RESPONSE SURFACE MODELING TO EVALUATE THE EFFECTS OF NONMEAT ADJUNCTS AND COMBINATIONS OF PSE AND RFN PORK ON THE TEXTURE OF BONELESS CURED PORK

Combinations of pale, sop, and exudative (PSE) and red, firm. and nonexudative (RFN) semimembranosus muscle were utilized to manufacture chunked and formed, cured pork. Response Surface Methodology was utilized to investigate the effects of soy protein concentrate (SPC), sodium caseinate (SC), and modified food starch (MFS) on bind and texture profile analysis. Fifteen adjunct formulations for five PSE and RFN combinations provided 75 treatments for each of three replications. As CIE L* values of raw muscle increased, protein-protein bind decreased (P<0.05). MFS, SC, and SPC decreased (P<0.05) cohesiveness. MFS and SC decreased (P<0.05) chewiness, and MFS decreased (P<0.05) hardness. Utilizing these adjuncts demonstrated that MFS improved texture in PSE and RFN pork. This research demonstrated that diluting RFN pork with no more than 25% PSE pork permits the formation of a high quality boneless deli ham roll.     

Curing-induced water mobility and distribution within intra- and extra-myofibrillar spaces of three pork qualities

This study introduces the use of nuclear magnetic resonance (NMR) relaxometry in the elucidation of the curing‐induced water mobility and distribution within pork. Fresh meat samples of three different meat qualities [normal; pale, soft and exudative (PSE); dark, firm and dry (DFD)] were cured by using different curing conditions (0.9–9% NaCl and 6% NaCl + 10 mm Na₄P₂O₇). Distributed NMR T₂ relaxation data revealed the presence of three distinct water populations (T_2b, T₂₁, T₂₂), with the T₂₁ population being most influenced by the curing conditions, which was reflected by strong correlations between the salt‐induced swelling and the mean relaxation time of the T₂₁ population. Consequently, the T₂₁ population reflects the myofibrillar swelling, and is an excellent indicator of myofibrillar geometry upon curing. Both the NMR data and the salt‐induced swelling capacity were highly dependent on fresh meat quality. Independent of brine composition, the DFD meat had a significantly higher swelling capacity than the two other meat qualities. A higher response to NaCl concentration on the swelling capacity was observed for PSE and normal meat than for DFD meat, which suggests interactions between the pH of the meat and NaCl‐induced swelling.