Freezing Effects on Quality, Bacteriology and Retail-Case Life of Pork

Freezing effects (?30°C, 90 days) on objective measures of muscle quality, bacterial growth and retail case life of thawed pale, soft, exudative, normal and dark, firm, dry pork were determined. Small but significant interactions (P lt; 0.05) did not interfere with interpretation of quality group and storage treatment effects. Frozen/thawed loin chops had slightly but significantly (P < 0.05) higher pH, less expressible juice, more soluble protein and darker color than fresh pork. The lag phase of bacterial growth was shorter in frozen/thawed pork, while the generation time was unaffected (P > 0.05). Freezing/ thawing significantly (P < 0.05) reduced case life due to appearance of chops but did not affect time for spoilage odors to develop.     

EFFECTS OF INHERENT MUSCLE QUALITY DIFFERENCES UPON THE PALATABILITY AND COOKING PROPERTIES OF VARIOUS FRESH, CURED AND PROCESSED PORK PRODUCTS

Ham steaks, loin chops, bacon slices, shoulder roasts and sausage patties fabricated from three muscle quality groups were utilized to evaluate the effects of muscle quality on palatability and cooking properties. Irrespective of muscle quality (pale, soft, exudative (PSE) versus normal versus dark, firm, dry (DFD)) all pork cuts evaluated were well within the acceptable range in palatability. In addition, results indicated that inherent muscle quality differences were of little relevance to the eating quality of pork. However, meaningful differences in cooking losses were observed from loin chops and bacon slices.     

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.     

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 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.     

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.     

PSE肉和DFD肉中糖原含量变化分析

利用蒽酮比色法进行检测正常肉、PSE肉和DFD肉中糖原含量的变化。糖原标液水解率为95.8%～98.7%,平均值为97.46%,相对标准偏差为1.25%。在0h,正常肉、PSE肉和DFD肉中糖原的平均含量分别为0.7560、0.7456、0.5284mg/g,RSD为0.3689%～0.7566%。PSE肉中糖原含量2h后下降到0.0420mg/g,RSD为2.3890%。正常肉和DFD肉的糖原含量在72h后分别下降到0.0608mg/g和0.0794mg/g,RSD为2.1445%和4.5931%。     

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.     

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.     

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.     

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.     

Effects of distribution packaging method and storage time on the physical properties and retail display characteristics of pork

The sensory characteristics of pork chops from bone-in loins and Boston butts (n = 65 each) were affected little by primal loin and the butt packaging method (paper wrap, vacuum pack and gas flush) and storage time (7, 10 and 14 days) under industry conditions. However, loin chops fabricated from vacuum-packaged loins after 14 days of storage had less (P < 0·05) discoloration and two-toning than chops fabricated from other loins. All loin chops were placed in retail display and overwrapped with a polyvinyl chloride film after fabrication at each storage time. Vacuum-packed butts stored for 10 and 14 days produced chops with less discoloration and two-toning, and higher overall appearance scores (P < 0·05) compared to chops from paper-wrapped or gas-flushed cuts. Vacuum-packaging resulted in higher quality retail cuts than paper-wrapped or gas-flushed packaging. Thus, it is recommended that the pork industry and retail distribution system utilize vacuum-packaging as the primary method to store and ship fresh pork before retail sale.     

The effects of differences in inherent muscle quality and frozen storage on the flavor and texture profiles of pork loin roasts

Complete flavor and texture profiles on pork loins from 118 carcasses revealed the following findings: (1) freezing, storing and thawing pork loins produced a slight tenderizing effect by making them less cohesive and easier to chew; permitted greater moisture release during chewing, thereby, slightly increasing the juiciness; resulted in a breakdown to more appropriate residual particles which resulted in a more appropriate, well balanced and blended texture; but resulted in a less appropriate and well balanced flavor; (2) pork with normal muscle quality had a firmer, more elastic, and cohesive texture which was stringier, more fibrous, and harder to compress, resulting in a slower breakdown to particles which tended to be fibrous, grainy and mealy; (3) the PSE condition appeared to result in a drier texture with less moisture and fat being released during mastication and a greater amount of moisture being absorbed from the mouth; (4) the DFD condition appeared to result in a juicier texture with greater amounts of fat and moisture being released into the mouth during mastication and a softer texture which was less cohesive, fibrous, and stringy and easier to chew, but as the DFD condition became extreme the texture became excessively soft, crumbly and mushy resulting in a relatively large proportion of small mealy and/or mushy particles which detracted from the texture amplitude; (5) the PSE condition resulted in a predominance of sour notes which detracted from the flavor amplitude, and possibly resulted from more extensive accumulation of lactic acid during postmortem glycolysis; and (6) the DFD condition resulted in a predominance of porky, sweet, and fatty character notes which enhanced the flavor amplitude but as the DFD condition became extreme, more character notes contributing to off-flavors were detected, a portion of which were apparently due to sex taint.

Present findings clearly document the influence of differences in inherent muscle quality on palatability properties of pork loins and aid in resolving the controversy that presently exists within the literature regarding the effects of freezing, frozen storage, and thawing on pork palatability. However, further research will be required to document the impact of such influences on consumer acceptance.     

Volatile production in irradiated normal, pale soft exudative (PSE) and dark firm dry (DFD) pork under different packaging and storage conditions

Normal, pale soft exudative (PSE) and dark firm dry (DFD) pork Longissimus dorsi muscles were vacuum packaged, irradiated at 0 or 4.5 kGy and stored at 4°C for 10 days. Volatile production from pork loins was determined at Day 0 and Day 10 of storage at 4°C. With both aerobic and vacuum packaging, irradiation increased the production of sulfur-containing volatiles (carbon disulfide, mercaptomethane, dimethyl sulfide, methyl thioacetate and dimethyl disulfide) in all three pork conditions at Day 0 but did not increase hexanal – the major indicator volatile of lipid oxidation. The PSE pork produced the lowest amount of total sulfur-containing volatiles in both aerobically and vacuum-packaged pork at Day 0. The majority of sulfur-containing volatiles produced in meat by irradiation disappeared during the 10-day storage period under aerobic packaging conditions. With vacuum packaging, however, all the volatiles produced by irradiation remained in the packaging bag during storage. Irradiation had no relationship with lipid oxidation-related volatiles (e.g. hexanal) in both aerobic and vacuum-packaged raw pork. The DFD muscle was very stable and resistant to oxidative changes in both irradiated and nonirradiated pork during storage, suggesting that irradiation can significantly increase the utilization of raw DFD pork and greatly benefit the pork industry.     

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。     

Differences in quality characteristics of normal, PSE and DFD pork

Differences in water-holding capacity, colour and tenderness/toughness were studied in 21 pork loins belonging to three quality categories, i.e. dark firm dry (DFD), normal and pale soft exudative (PSE). The division into the three groups was based upon the ultimate pH-values of the loins (< pH 5·5, pH 5·5-6·0, pH > 6·4). The PSE loins were characterized by a poor waterholding capacity, higher cooking loss and paler colour in contrast to the DFD category. The normal loins took an intermediate position. Neither sarcomere length, determined on fresh muscle tissue, nor Armour tenderometer values showed significant differences between the various quality categories. This was in contrast to the Warner-Bratzler (W-B) shear force values, determined on cooked loins, which had the lowest values in the DFD category. A strong relationship between the W-B values and the cooking losses was found. It was concluded that neither sarcomere length nor Armour tenderometer measurements were able to predict the shear force values of cooked pork loins.     

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。     

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.     

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.     

Development in myofibrillar water distribution of two pork qualities during 10-month freezer storage

The effects of fresh meat quality (PSE versus DFD), freezing temperature (-20°C versus -80C°) and duration of freezer storage on changes in water mobility and distribution were followed at intervals of 1-2 months during 10-month freezer storage of pork using low-field NMR T(2) relaxometry. Fresh meat quality was found to have a strong significant effect (P<0.0001) on the amount of loosely bound water (relaxation time >100ms) also after freezing, which was reflected in a significantly lower cooking yield in PSE meat compared with DFD meat (P<0.0001). While no significant changes in the cooking yield were observed with increasing length of freezer storage, NMR T(2) relaxation measurements revealed a significant increase in the amount of loosely bound water in PSE meat with increasing length of freezer storage. This finding indicates that NMR T(2) relaxation measurements are quite sensitive to freezing-induced changes in the meat structure, causing a shift in the distribution of water and possibly capable of detecting these before they are reflected in a reduced cooking yield. In addition, an interaction between fresh meat quality and effect of length of freezer storage on the amount of very mobile water easily lost as drip was observed, implying that PSE meat is more susceptible to freezer storage-induced deteriorative changes in the meat structure, causing a shift in the distribution of water, than DFD meat.