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.     

The effects of postmortem product handling and aging time on beef palatability

The effects of postmortem handling and aging time were investigated on the palatability attributes of beef at weekly intervals up to four weeks using both an experienced laboratory panel and a highly trained, flavour/texture profile panel. The presence of bone in intact meat cuts reduced both cooking times and cooking losses, irrespective of postmortem handling treatment. Bone-in (intact), vacuum packaged meat cuts were more tender initially and overall and had less perceived connective tissue and lower shear force values than conventionally aged controls and controlled atmosphere, boneless, display-ready cuts. Boneless, vacuum packaged cuts also were more tender overall than controlled atmosphere, boneless, display-ready cuts. Both bone-in (intact) and boneless, vacuum packaged cuts were rated higher in juiciness and flavour desirability than conventionally aged controls and controlled atmosphere, boneless, display-ready cuts. Bone-in (intact), vacuum packaged cuts were also perceived to have a more intense beef flavour than cuts receiving any other postmortem handling treatment. Consequently, both bone-in (intact) and boneless vacuum packaged cuts were rated higher in overall palatability than conventionally aged controls and controlled atmosphere, boneless, display-ready cuts. However, detailed flavour and texture profile analysis indicated steaks could be aged for up to four weeks without influencing the overall quality of the flavour or texture, irrespective of postmortem handling treatment. Both initial and overall tenderness improved progressively and Warner–Bratzler shear force values and the amount of perceived connective tissue decreased progressively as postmortem storage was extended. In addition, both flavour intensity and desirability increased progressively with the extension of postmortem aging. Consequently, postmortem aging appeared to be beneficial to all palatability attributes, except juiciness. Therefore, steaks can be aged for up to four weeks to obtain substantial improvements in overall texture, without adversely affecting overall flavour quality, irrespective of postmortem handling treatment.     

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.     

Dynamical Changes of Beef Intramuscular Connective Tissue and Muscle Fiber during Heating and their Effects on Beef Shear Force

Changes of meat shear force and its characteristics during cooking have been extensively studied, but great variability existed due to the cooking method among different studies. This study was designed to focus on the dynamic changes of beef intramuscular connective tissue (IMCT) and muscle fiber during water-bath heating and their effects on beef shear force. At 4 d postmortem, beef semitendinosus muscles were divided into 11 steaks and then cooked respectively to an internal temperature of 40, 50, 55, 60, 65, 70, 75, 80, 85, and 90°C (the remainder was not cooked as control). Collagen content and its solubility, transition temperature of perimysia and endomysia, fiber diameter, and Warner–Bratzler shear force values (WBSF) were determined. The results showed that fiber diameter decreased gradually during cooking, concomitant with the increases in filtering residue and WBSF. The maximum transition temperature (T _max) of endomysial components was lower than that of perimysial components (50.2 vs. 65.2°C). Muscle fiber and IMCT (especially perimysia) shrank during cooking, resulting in the increase of WBSF when the internal temperature was lower than 75°C, but further cooking led to the disintegration of perimysial structure, lowing up the increase of WBSF between 75 and 90°C. For beef semitendinosus muscle, the internal temperature of 65°C is a critical cooking point where meat gets tougher.     

Structural weakening of intramuscular connective tissue during conditioning of beef

The structural changes in intramuscular connective tissues endomysium and perimysium during conditioning of beef were investigated using an improved technique of scanning electron microscopy. In beef conditioned for 28 days of 4°C, the endomysium resolved into individual collagen fibrils and the thick sheets of perimysium separated into collagen fibres of 4-8 μm in diameter. These results provide direct evidence for the structural weakening of endomysium and perimysium during conditioning. The structural changes in the intramuscular connective tissue were minimal until 10 days post mortem, but clearly observable after 14 days post mortem. Therefore, it is concluded that intramuscular connective tissue shows the effect on tenderisation of extended conditioning (2-4 weeks) of beef.     

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.     

SHEAR FORCE ANALYSIS AS AN INDICATOR OF CHANGES IN MECHANICAL STRENGTH OF ISOLATED BEEF INTRAMUSCULAR CONNECTIVE TISSUE DURING AGING

Intramuscular connective tissue (IMCT) was isolated from bovine semitendinosus (ST) muscles aged 3, 5, 7, 10, 14, 21, 28, and 35 days postmortem. Shear force values were collected from raw ST muscle and IMCT preparations to determine changes in mechanical strength (resistance to shearing) of the connective tissue fibers during postmortem aging. Statistical analysis indicated significant differences in mean shear force values of isolated IMCT preparations between aging periods (P < 0.001) but no consistent pattern of change in shear force values was detected. No significant change in shear force values of raw ST muscle during postmortem aging (P > 0.05) was observed. Other investigators have incorporated the same procedure and reported decreasing shear force values with increased aging times for IMCT preparations and raw ST samples. Our results were not in agreement with these findings.     

Assay and Storage Conditions Affect Yield of Salt Soluble Protein from Muscle

Pork and beef muscles were used to evaluate assay and storage condition effects on yields of salt soluble protein (SSP). Assay conditions included pH (5.5, 6.0 or 6.5), extraction volume (6, 9, 12 or 15 X sample weight), homogenization time (30, 60, 90 or 120 set) and centrifugal force (2500, 4000 or 5500 ×g). Storage conditions included postmortem aging (4°C for 0, 7 or 14 days) and freezing conditions (rapid freezing, slow freezing, and freezing-thawing-freezing). Highest yield of SSP was obtained using pH 6.0, extraction volume 15 X sample weight, centrifugation at 4000 ×g and homogenization time 90 to 120 set for both pork and beef. Freezing conditions did not affect measurement of SSP. Aging beef for 7 and 14 days postmortem reduced the yield of SSP; however, such differences were not observed for pork.     

宰后成熟对牛胴体不同部位显微结构影响

将不同部位肉样真空包装后于4℃条件下成熟72h ,采用石蜡切片苏木精-伊红(HE)染色法、原子力显微镜扫描肌原纤维、环境扫描电镜扫描肌纤维膜、免疫组织化学法及测定剪切力,研究牛胴体不同部位剪切力、宰后成熟过程中肌纤维和肌原纤维裂解程度、肌纤维膜变化及μ-calpain肌纤维定位。结果表明：剪切力：半腱肌＞腹直肌＞背最长肌;牛肉后熟过程中,背最长肌肌纤维、肌原纤维裂解程度最大,腹直肌次之,半腱肌变化较小;肌纤维膜变化不大;μ-calpain主要存在于肌纤维膜和肌浆中,红肌纤维(慢肌)μ-calpain含量高,白肌纤维(快肌)μ-calpain含量低。μ-calpain在牛肉后熟过程中对牛肉嫩化具有重要作用,红肌纤维μ-calpain含量高,白肌纤维μ-calpain含量低,因此,胴体不同部位红肌纤维和白肌纤维的比例是导致其后熟嫩度和显微结构差异较大的一个重要因素。     

Early post-mortem degradation of intramuscular collagen

Post-mortem changes in physical and thermal stabilities of bovine intramuscular connective tissue were studied during the first 24 h postmortem. Collagen thermal shrinkage temperature (T(s)) decreased (P < 0·01) and collagen solubility increased (P < 0·01) during the first 24 h following slaughter with greatest amount of change occurring in the first 8 h post mortem. The dynamic nature of intramuscular connective tissue during the very early post-mortem (VEP) period is compared to the VEP-tenderness relationships proposed by Marsh and others.     

Muscle fiber properties and thermal stability of intramuscular connective tissue in porcine M. semimembranosus

BACKGROUND: Strips can be easily peeled from raw destructured pork (M. semimembranosus, SM muscle) by hand but in normal meat these strips break. In general, destructured meat is pale in color. Porcine SM muscles have thick muscle fibers which could predispose them to destructuration. This study investigated whether the onset and peak temperatures of thermal shrinkage (T_o and T_p) of intramuscular connective tissue from SM muscles were associated with muscle fiber thickness, capillary density or extracellular space. We also investigated whether these muscle fiber properties of destructured muscles differed from those of normal muscles. RESULTS: The destructured and normal muscles were similar in muscle fiber cross‐sectional area, capillary density, extracellular space and sarcomere length. T_o correlated negatively with sarcomere length. The water content of differential scanning calorimetry samples consisting of intramuscular connective tissue was higher in destructured muscles than in normal muscles. CONCLUSION: Muscle fiber properties (muscle fiber cross‐sectional area and sarcomere length) and capillary density are similar in destructured and normal SM muscles. T_o and T_p of intramuscular connective tissue are similar in destructured and normal muscles. Muscle fiber properties show no association with the thermal shrinkage properties of intramuscular connective tissue. Copyright © 2009 Society of Chemical Industry     

A Comparison of Some Properties of Beef and Buffalo (Bubalus bubalis) Meat

Assessments were made of the meat properties of four muscles of differing connective tissue content, from both Achilles tendon-hung and tenderstretched (suspended from the sacrosciatic ligament) sides of buffalo (Bubalus bubalis) and Brahman–cross steers of similar mean age (51 months) and carcass weight (ca 230 kg). Color measurements indicated that muscles from buffalo were darker although ultimate pH values of the groups did not differ. Adhesion, compression, and Warner-Bratzler peak shear force minus initial yield force values were significantly greater in buffalo than in beef muscles; indicating greater connective tissue contribution to toughness of buffalo meat. Taste panel assessment of muscles of relatively low connective tissue content in beef, indicated that generic differences in tenderness were slight although buffalo meat was less juicy than beef. Flavor and overall acceptability of buffalo meat were significantly less than for beef.     

EFFECTS OF DIFFERENT AGING PROCEDURES ON THE PALATABILITY OF BEEF

Ten pairs of beef strip loins were obtained 48 h postmortem from ten good grade beef carcasses. Three steaks (2.5 cm thick) were cut from the loin end of each strip loin and the remaining portion retained as the subprimal. Steaks and subprimals were aged for 7 days at 2°C in the following treatments: polyvinyl chloride overwrapped steaks (PVC-ST), vacuum packaged steaks (VP-ST), vacuum packaged subprimals (VP-SP), and subprimals held in air (Air-SP). After aging of the subprimal, 3 additional steaks were cut for evaluation. The steaks from all treatments were evaluated for palatability and chemical characteristics. Palatability characteristics did not differ significantly (P > 0.05) between treatments with the exception of the off-flavor intensity of PVC-ST which was higher (P < 0.05) than other treatments. Warner-Bratzler shear values were similar for all treatments. No significant differences (P > 0.05) were observed between treatments for percent moisture, percent lipid, pH or TBA number. The results of this study indicate that aging method (air or vacuum) or type of cut (steaks or subprimals) had little effect on the palatability attributes or chemical characteristics of the beef strip loins.     

Structural and biochemical characteristics of bovine intramuscular connective tissue and beef quality

The aim of the study was to evaluate the impact of structural and biochemical characteristics of muscle intramuscular connective tissue on beef quality. The experimental design was based on three muscles of three breeds sampled as fresh material and cooked at 55 °C (Longissimus thoracis and Semimembranosus) or at 70 °C (Semimembranosus and Biceps femoris) for quality assessment. The results showed that muscle characteristics influence beef quality differently from one muscle to another. In grilled LT, proteoglycan content contributed negatively to juiciness, and intramuscular lipids were linked positively to tenderness, flavour, residues and overall liking scores. In grilled SM, cross-link and lipid contents were involved in beef quality. In BF cooked to 70 °C, perimysial branch points were negatively linked to tenderness. In SM cooked to 70 °C, perimysial area was involved in beef quality. These results should allow a better understanding of the factors involved in background toughness, in juiciness and flavour of meat.     

AMPK活性对宰后牛肉糖酵解、肌肉内环境及品质的影响

为探究牛肉宰后成熟过程中单磷酸腺苷活化蛋白激酶（adenosine monophosphate-activated protein kinase,AMPK）对糖酵解、肌肉内环境及品质的影响,以0.50 mol/L 5-氨基咪唑-4-甲酰胺核苷（5-amino-4-imidazolecarboxamide,AICAR）处理的西杂牛背最长肌为对象,于4 ℃进行成熟,测定宰后成熟期间肌肉AMPKα基因（PRKAA1、PRKAA2）转录量、P-AMPK表达量、AMPK活性、糖酵解水平及品质指标的变化情况。结果表明：宰后24～120?h,处理组AMPKα基因转录量、P-AMPK表达量及AMPK活力均显著高于对照组（P＜0.05）;72～168?h,处理组pH值和肌糖原含量显著低于对照组（P＜0.05）,乳酸含量显著高于对照组（P＜0.05）;12～168?h,处理组L*、b*值及ATP、ADP、AMP和IMP含量均显著高于对照组（P＜0.05）,a*值显著低于对照组（P＜0.05）;24～120?h,处理组蒸煮损失率和肌原纤维小片化指数显著高于对照组（P＜0.05）,剪切力显著低于对照组（P＜0.05）。AICAR通过激活AMPK并加快宰后糖酵解影响肌肉内环境、肉色、剪切力及肌纤维微观结构变化,加快宰后肌肉成熟进程,说明AMPK活性对宰后肌肉糖酵解及品质变化具有重要影响,且可通过调控宰后肌肉AMPK活性来调节肌肉品质。     

Structural weakening of intramuscular connective tissue during post mortem ageing of chicken Semitendinosus muscle

The structural changes in intramuscular connective tissues endomysium and perimysium during post mortem ageing in chicken semitendinosus muscle were investigated using an improved technique of scanning electron microscopy. In post mortem chicken aged for 12 h at 4°C, the endomysium resolved into individual collagen fibrils and the perimysial sheets separated into collagen fibres. These results provide direct evidence for the structural weakening of endomysium and perimysium during post mortem ageing. The structural changes in the intramuscular connective tissue were minimal until 6 h post mortem, but clearly observable after 12 h post mortem. It was concluded that this disintegration of the intramuscular connective tissue is the chief mechanism in tenderisation during extended post mortem ageing of chicken.     

电刺激对牛背最长肌中钙激活酶活性及嫩度的影响

通过对中国杂交黄牛(鲁西黄牛×西门塔尔)牛背最长肌中Calpains活性及剪切力值的分析,研究了电刺激对牛背最长肌宰后成熟过程中Calpains活性及牛肉嫩度的影响。结果表明:电刺激显著提高了μ-calpain的活性(P<0.05),降低了calpastatin对μ-calpain的抑制作用,提高了牛背最长肌的嫩度,缩短了牛肉的成熟时间;但电刺激仅在宰后成熟1h,显著提高了m-calpain的活性(P<0.05);宰后成熟24h、3d,与对照组之间差异不显著(P>0.05),试验结果证实,电刺激通过对Calpains体系的影响,改变了牛肉的成熟速度,显著的改善了牛肉的嫩度。     

牛肉排酸成熟过程中的品质变化

为探究排酸成熟过程中肉类品质的变化,以牛肉为研究对象,测定排酸1～7 d肉样的硬度、保水性、pH值、肌原纤维小片化指数（myofibril fragmentation index,MFI）、菌落总数、大肠菌群数以及排酸1、3、5d时肌原纤维的超微结构。结果表明：牛肉排酸3 d时出现最大僵直期,硬度达到最高,保水性达到最低,pH值降到最低值5.56;随着解僵及成熟的进行,牛肉嫩度、保水性回升,排酸7 d时pH值回升到5.84,达到排酸成熟肉标准（5.8～6.2）;排酸1 d时,肌原纤维的Z线、粗细丝清晰可见,随着肌原纤维小片化程度的不断加深,排酸5d时,Z线变得模糊,几乎消失,成为晕染状,几何构型发生明显变化。上述结果表明,牛肉在0～4 ℃条件下排酸成熟需要7d,前3 d是排酸的关键时期。     

Partial least squares analysis of near-infrared hyperspectral images for beef tenderness prediction

Tenderness is a primary determinant of consumer satisfaction of beef steaks. The objective of this study was to implement and test near-infrared (NIR) hyperspectral imaging to forecast 14-day aged, cooked beef tenderness from the hyperspectral images of fresh ribeye steaks (n = 319) acquired at 3–5 day post-mortem. A pushbroom hyperspectral imaging system (wavelength range: 900–1700 nm) with a diffuse-flood lighting system was developed. After imaging, steaks were vacuum-packaged and aged until 14 days postmortem. After aging, the samples were cooked and slice shear force (SSF) values were collected as a tenderness reference. After reflectance calibration, a Region-of-Interest (ROI) of 150 × 300 pixels at the center of longissimus muscle was selected. Partial least squares regression (PLSR) was carried out on each ROI image to reduce the dimension along the spectral axis. Gray-level textural co-occurrence matrix analysis with two quantization levels (64 and 256) was conducted on the PLSR bands to extract second-order statistical textural features. These features were then used in a canonical discriminant model to predict three beef tenderness categories, namely tender (SSF ≤ 205.80 N), intermediate (205.80 N < SSF < 254.80 N), and tough (SSF ≥ 254.80 N). The model with a quantization level of 256 performed better than the one with a quantization level of 64. This model correctly classified 242 out of 314 samples with an overall accuracy of 77.0%. Fat, protein, and water absorption bands were identified between 900 and 1700 nm. Our results show that NIR hyperspectral imaging holds promise as an instrument for forecasting beef tenderness.     

A Comparison of Some Properties of Meat from Young Buffalo (Bubalus bubalis and Cattle

Meat properties of four muscles of differing collagen content from both Achilles tendon-hung and tenderstretched (suspended from the sacrosciatic ligament) sides of water buffalo (Bubalus bubalis) and Brahman-cross steers were assessed. The animals were together on good pasture until slaughtered at similar ages (27 months) and liveweights (ca 317 kg). Buffalo muscles were darker than beef and darkened more at chill temperatures. Warner-Bratzler peak force minus initial yield values, adhesion and compression values indicated that for the three muscles with the greater connective tissue contents, buffalo muscles were slightly tougher than corresponding beef muscles because of a greater contribution of connective tissue to toughness. No species differences were found for the psoas major muscle except for flavor, where beef was slightly preferred.