Quality characteristics of Chinese sausages made from PSE pork

Chinese sausages made from normal and different levels of PSE pork (100% Normal, 50%Normal+50% PSE and 100% PSE) were vacuum-packaged and stored at 4 °C for 45 days. The composition, processing yield, pH value, thiobarbituric acid (TBA) value, water activity, lactic acid bacteria counts and sensory properties of the meat products were evaluated. PSE pork loins had lower pH value, water holding capacity, moisture, fat and myofibrillar proteins content, but higher L^* value, drip loss and protein content than normal pork. Sausages made from 100% PSE pork had lower pH value, processing yield, moisture and fat content, but higher protein content than those of the 100% Normal and the 50% Normal+50% PSE treatments. Water activity was higher in the 100% PSE treatment than in other treatments. No differences in lactic acid bacterial counts among these treatments were observed. The pH values and water activity of the meat samples decreased, while lactic acid bacterial counts increased with storage time. TBA values among these treatments were not significantly different; however, the increase% of TBA values was higher for the 100% PSE treatment. TBA values of all treatments remained relatively low during storage. Chinese sausages made with 50–100% PSE pork had lower sensory texture, flavor and overall acceptability scores than the control samples, but were of acceptable quality.     

Changes in Microflora and Other Characteristics of Vacuum-packaged Pork Loins irradiated at 3.0 kGy

Effects of 3.0-kGy irradiation on microflora and other attributes of fresh, vacuum-packaged pork loins were examined during storage (2–4°C, 98 days) and mishandling (24–25°C, 24 and 48 hr). Shelf life of pork chops from irradiated loins was determined at 5°C. Irradiated loins kept at 2–4°C tested negative for Salmonella spp., Campylobacter spp., Clostridium perfringens and Staphylococcus aureus. Yersinia spp. was detected in pork chops held at 5°C; this organism, C. perfringens and Aeromonas spp. were present in abused samples. In two irradiated samples Listeria monocytogenes was found. Irradiation reduced aerobic, anaerobic and Aeromonas spp. counts; lactobacilli were least affected. Chemical spoilage began after 91 days at 2–4°C. With irradiation, TBA values were unaffected but Hunter a color values increased.     

Effects of dietary magnesium and duration of refrigerated storage on the quality of vacuum-packaged, boneless pork loins

Quality data were initially collected on 78 pork loins from crossbred pigs fed diets containing 0, 1.25 or 2.5% magnesium mica (MM). Loins were then vacuum-packaged, and randomly assigned to either 4 or 8 weeks of storage at 2°C. Dietary MM had no (P > 0.05) effect on moisture loss/retention or subjective and objective color measurements. Purge volume increased (P<0.05) and drip loss decreased (P<0.05) as storage time increased. Moreover, longissimus thoracis et lumborum (LM) chops became lighter (P<0.05), redder (P<0.05), and more yellow (P<0.05) during 8 weeks of storage. Although TBARS values increased linearly (P<0.001) during extended storage, LM chops from pigs fed 2.5% MM tended to have lower (P<0.07) TBARS values after 4 weeks of storage than chops from pigs fed 0 and 1.25% MM. After 8 weeks of storage, however, there was a tendency for TBARS values of chops from pigs fed 1.25% MM to be lower (P<0.07) than chops from pigs fed 2.5% MM. Even though feeding swine diets containing MM did not affect color and water-holding capacity of pork loins during storage, the data indicated inclusion of MM in swine diets may retard onset of oxidative rancidity in vacuum-packaged pork loins.     

Temperature abuse affects the quality of irradiated pork loins

The influence of temperature abuse on the quality of irradiated pork loins was investigated. Pork loins were obtained directly from a local packing plant, sliced and vacuum-packaged. Pork loins were randomly separated into 3 groups, sliced, and assigned to receive 0, 1.5, or 2.5 kGy electron-beam irradiation. Then, each chop was further cut into three equal pieces and assigned to three temperature treatments: Trt I was placed in a refrigerator directly after irradiation; Trt II was left at room temperature for 3 h before refrigeration; and Trt III was exposed at room temperature for 1 h three consecutive days with intermittent storage at 4 °C between exposures. Before irradiation, each loin pieces were vacuum-packaged. Color, 2-thiobarbituric acid reactive substances (TBARS), and volatiles were measured after 0, 14, 28 and 42 days of storage, and water-holding capacity and sensory characteristics of the loins were measured after 0, 14 and 28 days of storage. Temperature abuse had no significant effect on color, oxidation, and volatiles of irradiated pork loins. However, temperature abuse improved water-holding capacity of meat, which could be caused by the accelerated hydrolysis of muscle proteins at higher temperature. Irradiation increased redness, sulfur contents in volatiles and off-odor of pork loin. Off-odor and redness induced by irradiation sustained during storage. Among sulfur compounds, the content of dimethyl disulfide decreased gradually while the level of thiourea remained relatively constant. Irradiation also increased water loss, which might be related to the structural damage in membrane during irradiation. This study shows that temperature abuse has little effect on the quality of irradiated pork.     

Prediction of pork quality with near infrared spectroscopy (NIRS): 1. Feasibility and robustness of NIRS measurements at laboratory scale

The objective was to study prediction of pork quality by near infrared spectroscopy (NIRS) technology in the laboratory. A total of 131 commercial pork loin samples were measured with NIRS. Predictive equations were developed for drip loss %, colour L*, a*, b* and pH ultimate (pHu). Equations with R(2)>0.70 and residual prediction deviation (RPD)≥1.9 were considered as applicable to predict pork quality. For drip loss% the prediction equation was developed (R(2) 0.73, RPD 1.9) and 76% of those grouped superior and inferior samples were predicted within the groups. For colour L*, test-set samples were predicted with R(2) 0.75, RPD 2.0, colour a* R(2) 0.51, RPD 1.4, colour b* R(2) 0.55, RPD 1.5 and pHu R(2) 0.36, RPD 1.3. It is concluded that NIRS prediction equations could be developed to predict drip loss% and L*, of pork samples. NIRS equations for colour a*, b* and pHu were not applicable for the prediction of pork quality on commercially slaughtered pigs.     

RAW MATERIAL pH, PUMP LEVEL AND PUMP COMPOSITION ON QUALITY CHARACTERISTICS OF PORK

ABTRACT
Boneless, paired pork loins (n=120) were selected based on pH at 14 h postmortem. Ultimate pH, drip loss, instrumental color (L*, a*, and b* values), and proximate analysis were determined prior to pumping. Paired loins were cut into four sections and pumped to 100%, 106%, 112% or 118% of original weight to result in a product containing 0.4% sodium tripolyphosphate (STP) for Experiment 1 (Exp. 1) and 0.4% STP plus 0.4% salt for Experiment 2 (Exp. 2). In Exp. I, additional pump level increased (P<0.05) vacuum package purge. Higher raw materials pH reduced purge. A pump level x pH interaction (P<0.05) occurred for cook loss at 70C. In Exp. 2, increased raw materials pH reduced (P<0.05) purge loss and resulted in juicier, more tender pork. Pumped pork had higher (P<0.05) tenderness, juiciness, and saltiness scores than controls.     

SODIUM LACTATE EFFECTS ON MICROBIAL, SENSORY, AND PHYSICAL CHARACTERISTICS OF VACUUM-PACKAGED PORK SAUSAGE

Vacuum-packaged fresh meat products held at refrigeration temperatures have limited shelf-life expectancies, often due to growth of anaerobic lactic acid-producing bacteria. Agents that can suppress the growth of this group are beneficial. Fresh pork sausage, formulated to contain 0%, 1%, 2%, or 3% sodium lactate (SL), was vacuum packaged and stored at 4C for 0, 10, 17, 24, and 31 days. A trained sensory panel evaluated pork, salty, sour, and bitter flavors. Aerobic total plate counts (APC), anaerobic total plate counts (AnPC), aerobic lactic acid producers (ALC), anaerobic lactic acid producers (AnLC), TBA values, and pH were determined. SL depressed APC, AnPC, and AnLC. Addition of 1% SL extended shelf-life of vacuum-packaged fresh pork sausage by 1 week compared to controls; samples containing 2% and 3% SL had not reached spoilage level (log₁₀ 7.0 CFU/g) at the conclusion of this study. Addition of SL increased salty taste and prevented loss of pork flavor over time, but had no effect on sour or bitter flavors.     

Bacteriology and storage life of moisture-enhanced pork

This study was undertaken to determine the impact of the moisture enhancement process on the bacterial contamination and storage life of vacuum-packaged pork loins. Bone-in and boneless pork loins injected with brine (sodium chloride, sodium phosphate, lemon juice) were obtained from a commercial processing facility and stored for 5 weeks in vacuum packaging at 2 and 5 degrees C. At weekly intervals, samples were excised to determine numbers of spoilage bacteria and pathogens. The loins were subjectively evaluated by a sensory panel to quantify appearance and odor acceptability. Moisture-enhanced loins were initially contaminated with a population of psychrotrophic bacteria that was approximately 2 log units higher than that for noninjected boneless loins. This difference was largely due to contamination by larger numbers of pseudomonads in the brine-injected loins. There were no significant differences in the initial numbers of lactic acid bacteria, Enterobacteriaceae, or Brochothrix thermosphacta. Similar trends in spoilage bacterial populations were observed for moisture-enhanced loins with bones, but Enterobacteriaceae counts were also found to be approximately 1 log unit higher for the injected product. Brine-injected loins generally had larger bacterial numbers at each storage time, but there were no consistent injection treatment effects on bacterial growth. Brine injection did not affect color or odor deterioration, and the storage life for vacuum-packaged loins was the same as that for noninjected controls. The incidence of Listeria monocytogenes was 21% for control loins and 27% for moisture-enhanced loins. Although the brine injection process resulted in an increase in bacterial contamination, there was no evidence that this contamination would affect the storage life of vacuum-packaged loins, and further research is necessary to determine the significance of the increased incidence of L. monocytogenes.     

Survival of Campylobacter jejuni and Salmonella enterica Typhimurium in vacuum-packed, moisture-enhanced pork

The abilities of Campylobacter jejuni and Salmonella enterica Typhimurium to survive in vacuum-packaged, moisture-enhanced pork stored at 4 or 10°C were examined. Pork loins were surface inoculated with either C. jejuni or Salmonella Typhimurium and then moisture enhanced to a target of 10 or 20%. The enhanced pork loins were sliced 1 cm thick and vacuum packaged. A pork loin without moisture enhancement was sliced and vacuum packaged as a control. Samples were collected, plated, and the numbers of surviving organisms were determined periodically during storage at 4 and 10°C. The numbers of C. jejuni or Salmonella Typhimurium in samples with different moisture enhancement levels were similar (P > 0.05). No significant differences (P > 0.05) in C. jejuni counts were observed between samples at 10°C and those at 4°C. In contrast, the numbers of Salmonella Typhimurium in samples at 10°C had significantly (P < 0.05) increased (0.41 log CFU/g) from those at the refrigerated temperature of 4°C. Vacuum storage at 4 and 10°C for 28 days did not result in dramatic reductions in the mean numbers of C. jejuni and Salmonella Typhimurium. Our findings indicate that vacuum packaging under chilled conditions will not add substantially to safety for moisture-enhanced pork. Strict hygienic practices or the implementation of decontamination technologies is recommended.     

Comparison of indicators of microbial quality of meat during aerobic cold storage

This study was undertaken to evaluate various indicators for the prediction of the microbial quality of pork and beef loins during cold storage at 0 and 4 degrees C under aerobic conditions. Fresh loins of beef and pork were packaged aerobically and stored at 0 +/- 1 degrees C for 22 days and at 4 +/- 1 degrees C for 12 days or until the total plate counts (TPCs) for these loins exceeded 10(8) CFU/ml. During storage, samples were taken periodically for the measurement of TPCs, psychrotrophic bacterial counts, amine contents, volatile basic nitrogen (VBN) values, thiobarbituric acid values, D-glucose contents, L-lactate contents, pH, and electrical conductivity. Correlation coefficients were ca. 0.90 for all indicators except pH and conductivity. However, VBN and D-glucose contents showed the best correlation with bacterial counts at both temperatures for both beef and pork. Therefore, VBN and D-glucose could potentially be used as indicators in predicting the microbial quality of beef and pork during chilled storage under aerobic conditions.     

Influence of meat exudates on the quality characteristics of fresh and freeze-thawed pork

The influence of the accumulated exudates released from pork loin of itself on the quality characteristics of fresh and freeze-thawed pork during cold storage was investigated. Pork loins were divided into four groups (fresh pork with exudates, fresh pork without exudates, freeze-thawed pork with exudates and freeze-thawed pork without exudates) and stored at 1.0 °C for 7 days. Exudate amount increased due to freeze-thawing and with storage, and most quality traits such as drip loss, cooking loss, tenderness, lightness, redness, and moisture content were affected by freeze-thawing (p < 0.05). Freeze–thaw increased drip loss but decreased moisture content, cooking loss, tenderness, lightness and redness of meat (p < 0.05). Microbial growth was solely affected by exudate removal and the removal of initial exudates decreased microbial growth (p < 0.05). Exudates were positively correlated with total protein content and total plate count but negatively correlated with pH and cooking loss. Therefore, removing meat exudates and avoiding freeze can slow down the quality deterioration of pork during cold storage.     

Bayesian meta-analysis of the effect of fasting, transport and lairage times on four attributes of pork meat quality

Technological meat quality is a significant economic factor in pork production, and numerous publications have shown that it is strongly influenced both by genetic status and by rearing and slaughter conditions. The quality of meat is often described by meat pH at different times postmortem, as well as by color and drip loss. A meta-analysis based on a database built from 27 studies corresponding to a total of 6526 animals classified was carried out. The purpose of this meta-analysis was to study the effect of fasting, lairage and transport durations on four main attributes of the technological pork meat quality. A Bayesian hierarchical meta-regression approach was adopted.The results of our meta-analysis showed that fasting time had a significant effect on pH measured 24 h post-mortem (pHu) and drip loss (DL) measured in longissimus muscle. While, lairage affected only the pHu in semimembranosus muscle. Interestingly, we found that DL was the lone attribute that was affected by transport time and its interaction with fasting time.     

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.     

Textural attributes and oxidative stability of pork longissimus muscle injected with marbling-like emulsified lipids

The objective of the study was to create marbling-like fat in lean pork with acceptable oxidative stability through the injection of canola/olive oil-substituted emulsions. Pork loins were injected with 5% water as control (CW) or 5% emulsion containing no tocopherols (E) or 0.07% tocopherols (ET) and stored at 2 °C in an oxygen-enriched package for up to 3 weeks. Lipid oxidation was totally inhibited in ET pork but increased 3-fold to 0.20mg malonaldehyde/kg in CW and E pork after 3 weeks. ET treatment also had a positive effect on meat red color. Emulsion-containing pork, showing less protein oxidation (carbonyl and disulfide formation), had reduced drip loss and shear force than CW samples (P<0.05). The results indicated that incorporation of antioxidant-containing emulsions could create marbling-like texture in lean pork without compromising oxidative stability.     

Effects of Electrical Stimulation, Temperature of Boning and Storage Time on Bacterial Counts and Shelf-Life Characteristics of Beef Cuts

Strip loins and eye of rounds from 16 beef carcasses were used to study the effects of electrical stimulation (ES), no stimulation (NS), hot-boning (HB), and cold-boning (CB) on bacteriological and shelf-life evaluations. Following 7 days of vacuum-packaged storage, coliform counts were higher in the drip fluid from strip loins and lean surfaces of eye of rounds from ES compared to NS carcasses. A major advantage for HB in this study was the additional time required in retail display before the occurrence of lean surface discoloration. A previously identified benefit of lighter lean color with ES beef in carcass and primal cut form was also found in this study during display of retail cuts.     

The effect of stunning method on the incidence of PSE meat and haemorrhages in pork carcasses

Two commercial pig abattoirs (A and B) equipped with a head-only and head-to-chest electrical stunning systems, and two (C and D) equipped with compact carbon dioxide (CO(2)) stunning systems, were visited during 3 days to evaluate the effects of the stunning system on meat quality and haemorrhages. Meat quality was evaluated by measuring muscle electrical conductivity (PQM) and colour (Minolta Chromameter) at 2 and 7 h post mortem (abattoirs A and C, and B and D, respectively). PQM and colour were measured in 2486 and 2321 loins respectively. Also ultimate pH (pHu) was measured in 2395 loins at 24 h post mortem. Haemorrhages were evaluated by recording the incidence of petechiae, ecchymosis and haematomas, bone fractures were also recorded. A total of 1980 shoulders, 3943 loins, and 5438 hams were inspected. In the abattoirs equipped with the electrical stunning systems, a higher (P<0.05) incidence of potentially PSE meat (PQM>6) was found compared with the abattoirs equipped with CO(2) stunning. Likewise, the loins from electrically stunned pigs were paler than those from CO(2) stunned pigs (P<0.05). Electrical stunning increased the incidence of petechiae in the loin and the ham (P<0.05). No shoulder, loin or ham with bone fractures was found in the abattoirs studied. Therefore, CO(2) stunning reduces the incidence of PSE meat and of petechiae on muscle fascia of loins and hams, compared with electrical stunning. However, petechiae are not of great importance because they can be removed from the affected commercial cuts.     

Microbial profiles of commercial, vacuum-packaged, fresh pork of normal or short storage life

The microbial ecology of fresh vacuum-packed pork cuts during storage at -1.5 degrees C for up to 45 days was examined to characterize rates of microbial growth and pH changes in commercially prepared products of normal storage quality. Pork loins in commercial distribution with odour defects were also studied to determine a possible cause of the defects and avoid future problems. In addition, microbial profiles of pork cuts from two plants were compared, after storage for 25 days at -1.5 degrees C, to identify possible reasons for differences in the storage life of product from the plants. The effects of a change in sanitation procedures on the microbial populations of products stored for 25 days were also studied. With normal product, microbial growth in different packages progressed at different rates, reflecting differences in initial levels of bacterial contamination. All samples in the study reached 8 weeks without apparent organoleptic change and samples carried 5.8+/-1.2 log bacteria cm(-2) (mean+/-S.D.). The flora of loins with the odour defect were predominately lactic acid bacteria (LAB) and carnobacteria, but they contained large fractions of Enterobacteriaceae <35 days after packaging. Aeromonas spp. and Shewanella spp. were likely responsible for the sulfide-putrid smell of these spoiled products, but species of Enterobacteriaceae and lactic acid bacteria could have contributed to spoilage. Comparison of microbial groups present in 16 other cuts, half from each of two commercial plants, which were stored for 25 days at -1.5 degrees C, showed that larger fractions of Enterobacteriaceae were present in samples from the plant having difficulty achieving the desired storage life. Additional bacterial samples from 12 cuts supplied by the latter plant obtained after adoption of an acid sanitizer step in the plant cleaning regimen, and also stored for 25 days at -1.5 degrees C, yielded few Enterobacteriaceae, Aeromonas or Shewanella. Use of an acid sanitizer in plant cleaning may be a means of controlling alkali-tolerant bacteria such as Aeromonas or Shewanella which can contaminate pork cuts and spoil vacuum-packaged product. The fraction of Enterobacteriaceae in bacteria populations on fresh pork stored for 25 days at -1.5 degrees C may be a useful indicator of the effectiveness of plant sanitation.     

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.     

Combined effect of electron-beam (beta) irradiation and organic acids on shelf life of pork loins during cold storage

The combined effects of organic acids and irradiation on shelf life of pork loins were examined. Fresh pork loins were sprayed with organic acids (lactic, citric, and acetic) at 2%, packaged aerobically, and irradiated with an electron beam at 1, 2, and 3 kGy. During 14 days of storage, total plate count, coliform number, pH, and thiobarbituric acid-reactive substances were measured. Combinations of organic acid and irradiation were more effective in reducing and maintaining low total plate counts and coliform levels during storage than either treatment alone. Higher lipid oxidations were observed in all combination treatments at 1 day of storage than in the irradiation-only group. However, lower lipid oxidations were the result after 14 days of storage when combination treatments were used with irradiations of 2 and 3 kGy. Combined treatments involving lower irradiation doses than those required for irradiation alone could be used to extend the shelf life of pork loins during postirradiation storage without increasing lipid oxidation.     

Effect of Hydrodynamic Pressure Processing on the Processing and Quality Characteristics of Moisture-Enhanced Pork Loins

ABSTRACT: The objective of this study was to determine the influence of hydrodynamic pressure processing (HDP) and aging on the processing characteristics and final meat quality of moisture-enhanced pork loins. Boneless pork loins (n = 24) were split into 3 portions and assigned treatments: control (non-HDP treated, brine-injected), HDP treated before brine-injection, or HDP treated after brine-injection. Pork loins were injected with a salt/phosphate/water solution to 110% of original weight on day 0, intermittently tumbled 3 h, and then held overnight. Meat quality and protein characteristics were measured on days 1 and 8. HDP-treated loins had greater (P < 0.05) brine retention after overnight equilibration and a higher (P < 0.05) processing yield than controls. Warner–Bratzler shear force and expressible moisture decreased (P < 0.0001) with aging from days 1 to 8, but were not significantly affected by either HDP treatment. When the drip loss data from HDP treatments were pooled, HDP samples had lower drip loss values than controls. L* and b* measurements exhibited significant HDP by aging interaction effects, but a* was not influenced by either HDP or aging. Myofibrillar protein solubility and gel electrophoresis measurements of protein degradation were influenced by aging treatments. Data from this study suggest that HDP may have beneficial effects on the processing and final product quality of moisture-enhanced pork loins. Practical Application: This study demonstrates that hydrodynamic pressure processing (HDP) is an effective postharvest technology for improving the processing and meat quality characteristics of moisture-enhanced pork loin products, benefiting both meat processors and consumers.