Alterations in the sarcoplasmic protein fraction of beef muscle with postmortem aging and hydrodynamic pressure processing

Abstract: Capillary electrophoresis (CE) and reversed‐phase high performance liquid chromatography (RP‐HPLC) analyses were utilized to detect differences in the sarcoplasmic protein fractions of beef strip loins subjected to aging and hydrodynamic pressure processing (HDP) treatments. At 48 h postmortem, strip loins (n= 12) were halved and subjected to control or HDP treatments. Following treatment, each half was divided into 3 portions which were aged for 0, 5, and 8 d. After each aging period, steaks were removed for Warner–Bratzler shear force (WBSF) analysis and for the extraction of sarcoplasmic proteins which were analyzed by CE and RP‐HPLC. Aging by HDP interactions were not detected using either separation technique. With CE analysis, no HDP effects were observed; however, the relative peak area of 8 protein peaks ranging in size from 17 to >200 kDa were influenced by postmortem aging. Separation of proteins by RP‐HPLC demonstrated that HDP influenced the relative size of 2 protein peaks while postmortem aging effects were observed in 6 peaks. Alterations in the sarcoplasmic protein fractions detected by both CE and RP‐HPLC were correlated to WBSF measurements. Overall, data demonstrate that HDP has minimal effects on sarcoplasmic proteins and that aging related changes in the water soluble protein fractions of muscle may be useful as indirect indicators of beef tenderness. Practical Application: Using 2 different postmortem tenderization techniques, aging and hydrodynamic pressure processing, this study demonstrates that postmortem changes in the soluble protein fraction of beef may be useful as potential indicators of meat tenderness.     

Comparison of hydrostatic and hydrodynamic pressure to inactivate foodborne viruses

The effect of high hydrostatic pressure (HPP) and hydrodynamic pressure (HDP), in combination with chemical treatments, was evaluated for inactivation of foodborne viruses and non-pathogenic surrogates in a pork sausage product. Sausages were immersed in distilled water, 100-ppm EDTA, or 2% lactoferrin, and then inoculated with feline calicivirus (FCV), hepatitis A virus (HAV) or bacteriophage (MS2, phiX174, or T₄). Each piece was packaged individually and subjected to pressure by either HDP, HPP (500 MPa, 5 min, 4 °C), or control (no pressure). On sausages immersed in water, HPP and HDP significantly (P < 0.05) reduced titers of FCV by 2.89 and 2.70 log₁₀ TCID₅₀/ml, and HAV by log₁₀ 3.23 and 1.10, respectively, when compared to non-pressure-treated controls. Titers of T₄ (1.48 and 1.10 log₁₀ PFU/g) and MS2 (1.46 and 0.96 log₁₀ PFU/g) were also significantly reduced by HPP and HDP treatments, respectively, in combination with water. Inoculation of viruses and bacteriophage on a meat product may have protected viruses from complete inactivation by pressure treatments.

Industrial relevance

This is the first study to directly compare hydrostatic and hydrodynamic pressure technologies to inactivate microorganisms. This is also the first study to examine the inactivation of viruses and bacteriophages by pressure technology in a deli meat product. This study shows that viruses attached to meat surfaces may be protected from complete inactivation by hydrostatic and hydrodynamic pressure treatments, and these findings require more investigation into the survival of viruses in deli meat products.     

Kiwifruit protease extract injection reduces toughness of pork loin muscle induced by freeze–thaw abuse

Kiwifruit juice injection was used to tenderize freeze–thaw abused porcine meat, and the enzyme activity in relation to meat tenderness was determined. Whole pork loins (Longissimus lumborum) were subjected to 5 freeze–thaw cycles (–29 °C ↔ 4 °C). Non-frozen control and freeze–thaw treated loins were either non-injected or injected with 10% water or diluted kiwifruit juice (meat weight basis). After 48 h of incubation, samples were analyzed for pH, proteolysis, cooking loss, and Warner-Bratzler shear force. Shear force of meat increased 2-fold (P < 0.05) after 1 freeze–thaw cycle but decreased when loins were subjected to additional freeze–thaw treatments. The kiwifruit juice injection lowered the pH of meat from 5.6 to 5.2 and increased the cooking loss from 21% to 30% (P < 0.05). However, as indicated by the shear force reduction, tenderness of meat improved more than 2-fold (P < 0.05) after kiwifruit juice injection, in agreement with the SDS–PAGE patterns that showed substantial degradation of myosin in samples treated with kiwifruit juice. The actinidin assay confirmed the existence of significant proteolytic activity in kiwifruit juice extract and in injected loin samples, i.e., 4.65 units/mL and 1.27 units/g, respectively.     

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.     

DISTRIBUTION PACKAGING METHOD AND STORAGE TIME EFFECTS ON THE MICROBIOLOGICAL CHARACTERISTICS AND INCIDENCE OF THE PATHOGENS LISTERIA MONOCYTOGENES AND SALMONELLA IN PORK1

Microbiological and yield characteristics were determined on bone-in pork loins and Boston butts (n = 65 each) that were selected from a commercial facility and subjected to one of three packaging treatments: (1) paper wrapped, (2) modified atmosphere packaging (66% O, 2.26% CO₂ and 8% N₂), and (3) vacuum packaging. Cuts were stored up to 21 days at 0 ± 2C for yield characteristics and an added 28 and 35 days for microbiological characteristics. Treatment and storage effects on the incidence of the pathogens Listeria monocytogenes, Salmonella and numbers of aerobic bacteria, lactic acid bacteria and coliforms were determined. The amount of purge was variable (100 to 500 g) among packaging treatments. The vacuum packaged and modified atmosphere packed pork loins and butts had lower aerobic plate counts (P < .05) compared with the paper wrapped loins and butts. The numbers of Listeria species decreased at a greater rate for the vacuum packaged and modified atmospheric packaged pork loins compared with the paper wrapped loins. No Salmonella were found on meat from any packaging treatment or storage time. The microbial quality of pork loins and butts can be improved by using vacuum packaging compared with paper wrapping or modified atmosphere packaging.     

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.     

Changes in the content of biologically active polyamines during pork loin storage and culinary treatments

Dietary polyamines putrescine (PUT), spermidine (SPD) and spermine (SPM) participate in numerous human physiological processes, including tumour growth. Physicians and dieticians thus need reliable information on their contents in foods. However, data for processed meat are rather limited. Eight experiments with pork loin were therefore carried out. Loins were stored at −18 °C for 168 days in three experiments, in next three ones pork was stored aerobically, vacuum-packaged and packaged in a modified atmosphere (70% N₂ and 30% CO₂, v/v) at +2 °C for 9, 21 and 21 days, respectively. The effects of five usual culinary treatments were tested in two experiments. The polyamines were determined as dansyl derivatives using a HPLC method. Only SPM was determined at levels 20.3–25.2 mg kg⁻¹ in fresh loins; PUT and SPD contents were below the detection limits. SPM content slightly, but significantly (P < 0.05) increased during frozen storage, while it mildly and insignificantly (P > 0.05) decreased during all three variants of cold storage. SPM losses of about 40% of the initial content were observed during boiling, stewing, pan-roasting without oil and breaded pork frying, while roasting caused the loss of about 55%. Similar losses were found for loins processed 24 h and 7 days after slaughter. No SPM content was detectable in broth and grease produced during the processing.     

Technological properties and selected safety aspects of different cuts of organic and conventional pork

The present study aimed at evaluating and comparing technological quality and selected safety aspects of commercial organic and conventional pork cuts. The technological value was determined on the basis of pH value, centrifugation loss, cooking loss, drip loss, colour parameters (as measured with L*a*b* system), total heme pigments and total heme iron. The meat safety was verified based on the content of nitrate, nitrite, cadmium, lead, total microbial count, number of Listeria monocytogenes and Salmonella. The results indicated that organic meat had higher content of heme pigments and heme iron than conventional meat. The rearing system had no effect on the lightness. The organic loins and shoulders were redder and yellower than conventional ones. Neither organic nor conventional meat cuts were contaminated by pathogenic bacteria and nitrite/nitrate residues. Legal requirements concerning cadmium content were met for all the tested samples, whereas concerning lead only for organic loins.     

Microstructure alterations in beef intramuscular connective tissue caused by hydrodynamic pressure processing

Scanning electron microscopy (SEM) was utilized to evaluate microstructural changes in intramuscular connective tissue of beef semimembranosus muscle subjected to hydrodynamic pressure processing (HDP). Samples were HDP treated in a plastic container (HDP-PC) or a steel commercial unit (HDP-CU). Control and HDP samples were obtained immediately post-treatment and after 14 days of aging for SEM and Warner–Bratzler shear force (WBSF) analysis. Immediately post-treatment, HDP treated samples exhibited lower (P < 0.01) WBSF than did controls. After aging, HDP-PC samples had lower (P < 0.01) WBSF than that of aged controls. SEM analysis indicated that HDP-PC treatment disrupted the integrity of the collagen fibril network of the endomysium in both the non-aged and aged samples. Aging effects on the intramuscular connective tissue were observed in the HDP-PC and control samples. Both WBSF and connective tissue changes were greater in the HDP-PC than in the HDP-CU treated samples. Data suggest that shockwave alterations to connective tissue contribute to the meat tenderization of HDP.     

Effects of dry,vacuum, and special bag aging; USDA quality grade; and end-point temperature on yields and eating quality of beef Longissimus lumborum steaks

This study evaluated the effects of three aging methods: (dry (D), wet (W), and special bag (SB)); two quality grades [USDA Choice((≥ Small⁵⁰ marbling) and Select); and two cooked end-point temperatures (62.8 °C and 71.1 °C) on physico-chemical traits of instrumental tenderness, color, and sensory properties of Longissimus lumborum beef muscle. Dry-aged loins had higher (P < 0.0001) weight loss than W or SB aged loins. However, D and SB aged loins had similar (P > 0.05) combined losses. W aged loins had higher (P < 0.01) L* values than D or SB aged loins. Warner–Bratzler shear force of steaks was not affected (P > 0.05) by aging method or quality grade but increased (P < 0.0001) as end-point temperature increased. Sensory panel evaluation also showed no effect (P > 0.05) of aging method or quality grade on myofibrillar tenderness, juiciness, connective tissue amount, overall tenderness or off flavor intensity. Steaks cooked to 62.8 °C were juicier (P < 0.05) than those cooked to 71.1 °C. Neither D nor SB aging had advantages over W aging.     

Bacterial contamination of recirculating brine used in the commercial production of moisture-enhanced pork

In a commercial process for the production of moisture-enhanced pork, boneless pork loins were conveyed through a recirculating injection apparatus, and brine (sodium phosphate, sodium chloride, and lemon juice solids) was pumped into the meat through banks of needles inserted automatically into the upper surfaces of cuts. Brine samples were collected at intervals during the production process and analyzed to determine the total plate count and the numbers of lactic acid bacteria, pseudomonads, Brochothrix thermosphacta, and Enterobacteriaceae. Listeria monocytogenes numbers in the brine were determined using a PCR with primers for the hemolysin gene in combination with a most probable numbers determination. Maximum numbers of bacteria (log CFU/ml) recovered from the brine after 2.5 h of recirculation were as follows: total plate count, 4.50; lactic acid bacteria, 2.99; pseudomonads, 3.95; B. thermosphacta, 2.79; and enterics, 3.01. There was an increase in the number of L. monocytogenes in the recirculating brine with time, reaching a maximum of 2.34 log CFU/100 ml after 2.5 h of moisture-enhanced pork production. Thus, recirculating brines can harbor large populations of spoilage bacteria and L. monocytogenes and are an important source of contamination for moisture-enhanced pork.     

Effect of acid whey on physicochemical characteristics of dry‐cured organic pork loins without nitrite

The present study deals with the effect of acid whey (AW) on physicochemical properties of non‐nitrite organic dry‐cured pork loins. The loins were divided into three experimental batches: with the curing mixture (C), with sea salt (S) and with sea salt combined with AW (SW). The evolution of physicochemical properties, colour, fatty acid profile and microbiological quality were assessed at 0, 30 and 90 days of refrigerated storage. Physicochemical parameters of dry‐cured organic loins were significantly (P < 0.01) affected by treatment, storage time and the interaction between them. Sea salt in combination with AW was the most successful at reducing the browning reaction involved in the formation of dark colour in dry‐cured loins. Significant reduction in a* value (P < 0.05) caused by replacement of curing salt by sea salt has been less pronounced in sample with AW. Storage diminished (P < 0.01) initial differences in profile of SFA, MUFA and n‐3 induced by treatment method. AW added to uncured loins was able to protect PUFA against oxidation comparable to nitrite. The highest count of lactic acid bacteria (LAB) in dry‐cured loins with AW was accompanied by their lower pH (P < 0.05).     

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.     

磷脂酶活性对冷却肉持水性的影响

对正常肉和PSE肉样的肉质特性和磷脂酶活性进行了测定和分析。宰后PSE肉的pH1h和pH24h低于正常肉,而L值(宰后1h、24h)、脂肪氧化程度、汁液流失率、贮藏损失、蒸煮损失和磷脂酶A2总活性明显高于正常肉。冷却肉的汁液流失率与pH1h和pH24h呈强负相关,与T1h、磷脂酶A2总活性和非钙依赖型磷脂酶A2呈显著正相关。结果说明,宰后的低pH、宰后早期肌肉高温和磷脂酶A2活性对冷却肉汁液流失有重要作用。     

Effect of plasma-activated organic acids against Salmonella Typhimurium and Escherichia coli O157:H7 inoculated on pork loin and its quality characteristics

This study investigated the effectiveness of plasma-activated organic acid (PAOA) on pork loin's bactericidal impact and quality. Salmonella Typhimurium, Escherichia coli O157:H7, and Listeria monocytogenes were used to inoculate the pork loins, revealing that PAOA achieved approximately 1.0 log CUF/g greater reduction than plasma-activated water. This was attributed to PAOA's lower pH, elevated oxidation-reduction potential, and increased reactive oxygen species concentrations. Notably, 0.5% plasma-activated acetic acid (PAA) showed 1.5 and 0.6 log CFU/g higher synergistic bactericidal effect against S. Typhimurium and E. coli O157:H7, respectively, compared to acetic acid. PAA also outperformed other PAOA treatments in terms of pork quality with similar meat color to deionized water, no adverse effect on lipid oxidation, and significantly reduced protein oxidation. Sensory analysis revealed PAA's highest umami taste. Thus, PAA is a promising method for microbial control in the meat industry while enhancing the oxidative stability and umami taste of pork loin.Industrial relevanceThis study demonstrated the industrial potential of combining plasma and organic acid treatments to control microorganisms in meat production and processing, while improving storage quality and sensory attributes. By using plasma- activated acetic acid, the oxidative stability of meat was enhanced during storage and umami taste was improved. This innovative technology offers advantages such as ease of operation and large-scale production, and it may help to overcome consumer concerns regarding the overuse of chlorine-based disinfectants, as organic acids are commonly used food additives.     

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.     

Rapid Chilling and Mechanical Portioning as a Fresh Pork Processing System

Several rapid chilling techniques were applied after a variable delay time in an effort to link hot pork processing and mechanical portioning. Boneless pork loins (n = 80) were removed (1, 3 or 5 hr post-stunning) and assigned to one of three rapid chilling treatments: brine chilling, CO₂ gas or CO₂ snow. These were compared to the traditional method of chilling the carcasses 24 hr prior to blast freezing of excised loins. Loins were chilled until crust frozen, then tempered and mechanically portioned. Muscle color, pH, and sarcomere lengths were measured. Cooked chops were evaluated by taste panel and Warner-Bratzer shear force. There were no major differences in these parameters between rapid chilling methods when a delay time of at least 3 hr was used.     

Effects of dry aging of bone-in and boneless strip loins using two aging processes for two aging times

This experiment investigated the combined effects of two dry-aging methods (unpackaged and in a bag), two loin-cut styles (bone-in shell loins and boneless strip loins), and two aging times (21 and 28 days) on the physical, chemical, sensory, and microbial properties of dry-aged beef. Sections from shell and strip loin were assigned randomly to be aged unpackaged or aged packaged in a bag with high moisture permeability. Weight losses increased with aging time. Shell loins lost more (P < 0.05) weight during aging compared with strip loins; dry aging in a bag had less (P < 0.05) weight loss than unpackaged aging. There were no differences (P > 0.05) in any of the sensory traits between shell and strip loins or dry aging using a traditional method or in a bag. Dry aging in a bag creates positive effects on yields, no negative effects on product quality, and adds flexibility and control of the aging environment.     

Effect of lamb age and retail packaging types on the quality of long-term chilled lamb loins

The objective of this study was to determine the impact of lamb age and packaging types on meat quality. Paired loins (M. longissimus dorsi) were obtained from 36 carcasses that included 4-month-old (New season; NS) and 11-month-old lambs (Old season; OS). The loins were vacuum-stored for eight weeks at − 1.5 °C. After storage, the loins were cut into subsamples and were randomly assigned to either high-oxygen modified atmosphere packaging (HiOx-MAP) or PVC-overwrapping for further display for 8 days. No differences between the age classes in shear force and drip loss were found (P > 0.05). OS loins had significantly higher myoglobin and redness compared with NS loins. HiOx-MAP initially induced a more intense red colour compared with PVC (P < 0.05), but resulted in severe discolouration at the end of display regardless of the age class. This observation suggests that the retail packaging type is the dominant factor over the age on lamb colour stability.     

Measurement of Muscle Exudate Protein Composition as an Indicator of Beef Tenderness

The objective of this study was to determine the relationship between the protein composition of muscle exudates and meat tenderness in beef. Frozen, intact beef strip loins (n = 24) were each divided into 3 equal portions (anterior, middle, and posterior). Steaks were removed from each portion, individually vacuum packaged, thawed at 4 °C, and aged for 0, 7, or 14 d. After the designated aging period, exudate was collected from the packaging and 1 steak from each strip loin portion was utilized for shear force measurements. Muscle exudates were analyzed for protein content (biuret assay) and composition (sodium dodecyl sulfate–polyacrylamide gel electrophoresis). Shear force decreased (P < 0.0001) with aging from 0 to 14 d. The protein concentrations of the muscle exudates were not influenced by the aging period and were not related to the amount of exudate expressed. Electrophoretic analyses of the muscle exudates indicated that with aging the relative abundance of 4 proteins decreased (P < 0.01) and 10 proteins increased (P < 0.05) within the protein profiles of the exudates. The relative abundance of the 167, 97, and 47 kDa proteins in exudates at day 0 were significantly correlated (|r| = 0.57 to 0.77) to shear force at day 14. These data demonstrate that exudate protein composition changes with postmortem aging and beef tenderness.