Effects of fattening on post-mortem pH of beef muscles

The pH of beef psoas major (PM) and longissimus dorsi (LD) muscles at 1·0 h after slaughter were examined among the following four groups: pithed fattening cattle (FP), non-pithed fattening cattle (FN), pithed calves (CP) and non-pithed calves (CN). Differences were observed only in PM muscles. The levels of pH were in the order of FP相似文献   

Effects of early post-mortem pH and temperature on beef tenderness

The tenderness of loin steaks, prepared from beef sides after chilling, is strongly influenced by muscle temperature in the first 3 h after slaughter. Maintenance of about 37°C within the Longissimus muscle during this time, whether by heavy fat cover or by ambient-temperature manipulation, results in appreciable tenderness enhancement. Early post-mortem muscle pH (which varies over a wide range) also affects tenderness significantly; provided early and exceptionally fast chilling does not induce cold shortening, slow glycolysis promotes tenderness. Low-frequency (2 Hz) electrical stimulation, which accelerates glycolysis but causes negligible tissue disruption, significantly toughens the loin; in its normal mode (50–60 Hz), therefore, stimulation produces its desirable tenderising effect mainly—and perhaps solely—by fibre fracture.     

Determinants of tenderisation in beef Longissimus dorsi and Triceps brachii muscles

Tenderisation of bovine Mm. longissimus dorsi and triceps brachii and factors impacting tenderisation were studied. Mm. longissimus dorsi and triceps brachii of 12 Friesian-Holstein cows (age 3-11 years; 212-349 kg carcass weight) were sampled at various times post mortem (p.m.) for determination of pH, temperature, fibre type and morphology, connective tissue distribution, SDS-PAGE of myofibrillar proteins, Warner-Bratzler shear force, sarcomere length and osmolality. The stretched position of the M. triceps brachii (sarcomere length 2.35 ± 0.24 μm) resulted in a relatively low shear force at 1 day p.m. (6.2 ± 0.9 kg/cm(2)) with further storage having little additional effect. M. longissimus dorsi entered rigor in a more contracted state (sarcomere length 1.65 ± 0.11 μm), resulting in a relatively high shear force at 1 day p.m. (10.3 ± 2.3). Stepwise linear regression was used to calculate the best 1- to 3-variable equations for shear force of M. longissimus dorsi at 1, 7 and 14 days p.m. and the decrease in shear force between 7 and 14 days p.m. Shear force at 1 day p.m. appeared to be determined mainly by the speed of pH- and temperature-decline. Proteolysis of myofibrillar proteins and animal age appeared to be the main determinants for shear force at 1 and 14 days p.m. The average surface area of type I fibres could explain part of the variation in the decrease in shear force between 1 and 14 days p.m.     

Glycogen determination in post-mortem beef muscles

Different opinions are held regarding the stoichiometric conversion of glycogen into the intermediate metabolites of glycolysis and into lactate in post-mortem muscle. Results suggest that this could be due to difficulties in assessing glycogen content. In the present study it was found that glycogen was particularly difficult to analyse in beef of a high ultimate pH, but no apparent explanation for this can be given. Four different methods involving enzymatic hydrolysis and acid hydrolysis were compared for measurement of glycogen. It was found that enzymatic hydrolysis was preferable and that the glycogen method should include boiling, particularly if the samples had been frozen for several months. Prolonged freezer storage decreased the glycogen values obtained by about 15–25%. Stoichiometry in the conversion of glycogen into intermediates of the Embden-Meyerhof pathway and lactate was found if glycerol-3-phosphate was taken into consideration and the results were adjusted for the effect of freezer storage.     

The influence of ante-mortem treatment on relationship between pH and tenderness of beef

Longissimus lumborum et thoracis muscles from 150 cattle comprising Czech Pied breed bulls and cows were used to investigate the relationship between pH value and beef tenderness as influenced by housing before slaughter and by the hanging mode of carcasses. The pH value was measured in the loin at the end of the slaughter-line (pH(0)) and after cooling of carcasses (pH(24),pH(48)). The texture of raw meat was measured 72h post-mortem by the Warner-Bratzler shear method; the shear force was related to pH. Curvilinear relationships with coefficients of correlation r=0.64 (P<0.05) for bulls individually housed and r=0.83 for bulls housed in groups between the shear force and the pH value 24h p.m. were found with maximal shear force (the most tough meat) in the range of pH(24) from 6.2 to 6.4. Lower correlations (r=0.72 and r=0.54) between pH(24) and meat tenderness were found in the case of cows individually housed and housed in groups, respectively. No significant relationships were found between texture and pH measured at the end of the slaughter-line (r=0.59 for bulls and r=0.65 for cows) and 48h post-mortem (r=0.64 for bulls and r=0.50 for cows). The mode of housing of cattle before slaughter influenced the properties of beef significantly. Meat of bulls housed in groups before slaughter was less tender (the shear force was higher) than meat of bulls individually housed. It could be explained by higher depletion of glycogen before slaughter and thus insufficient pH decline. Generally, the meat of cows was more tender than of bulls irrespective of housing. No significant differences were found between the left and right halves of carcasses. Thus the mode of hanging had no influence on beef tenderness.     

The relationship between post-mortem calcium concentration or pH and indicators of proteolysis in ovine muscle

The relationship between post-mortem calcium concentration in muscle and indicators of proteolysis was examined and compared with pH as a predictor of these changes. Muscle samples (m. longissimus et thoracis lumborum; LTL) were obtained from the left side of 24 lamb carcasses at pH 6.2 and 6.0 and then at 1 and 2 days post-mortem (n=96). Alternate carcasses were electrically stimulated (low voltage) within 15 min of death. The myofibrillar fragmentation index (MFI) was determined on samples taken at pH 6.2 and 1 and 2 days post-mortem (n=72). Protein solubility, pH and free calcium concentration were measured on all samples (n=96). The post-mortem degradation of myofibrillar proteins was followed using SDS electrophoresis on all samples (n=96) from which the relative amounts of the 30 kDa fragment and a protein designated M1 were quantified. Transformation of data values for each variable (MFI, protein solubility, 30 kDa fragment and protein M1) improved the normality of the residuals and increased the variance explained by either calcium concentration or pH. pH was a better predictor of MFI and the 30-kDa fragment than calcium concentration and this was reversed when protein solubility and the protein designated M1 was predicted. Of the variables protein solubility could be predicted with the greatest accuracy using calcium concentration (R²=0.64; R.S.D.=0.81) or pH (R²=0.60; R.S.D.=0.85). However overall calcium concentration was not superior to pH as a predictor of the changes in the different indicators of proteolysis examined in this study.     

The relationship between water-holding capacity and cooked meat tenderness in some beef muscles as influenced by acidic conditions below the ultimate pH

Previous studies have indicated the beneficial influence of higher than normal ultimate pH (pH(u)) on the tenderness of cooked meat. Such benefits have been indirectly linked to the influence of increased pH on the water-holding capacity (WHC) of meat above the iso-electric point (IEP) of the myofibrillar proteins. In the present study, relationships between WHC and the tenderness of some beef muscles were investigated under pH conditions within and below the IEP of the myofibrillar proteins, such that the maximum range of meat swelling was achieved. It was found that increased WHC, as measured by swelling ratio in both raw and cooked meat, markedly influenced cooked meat tenderness, irrespective of the connective tissue content of the muscles. The results fitted a series of exponential decay equations relating swelling ratio to cooked meat toughness. Additionally, strong linear decreases in toughness were apparent over the pH range 4·6 to 4·1 for the three muscle types studied.     

Mechanical tenderisation of beef muscles for use in re-formed joints made with a cold-set binder

Three treatments, blade tenderisation (BT), needle tenderisation (NT) and enhancement by brine injection + vacuum-pulsing (VP), were applied to each of two muscles from beef forequarter, M. pectoralis profundus and M. supraspinatus, and two from the round of the hindquarter, M. semimembranosus and M. vastus lateralis. The tenderised muscles and non-treated controls were re-formed into joints using a cold-set bonding agent and tested as steaks cut from the joints. NT and VP gave a similar degree of tenderisation, as indicated by W–B shear force and taste panel, while BT had a lesser but still significant effect. Cook loss from steaks was increased by BT and NT treatments for the, tougher, forequarter but not the hindquarter muscles. The overall conclusion was that NT and VP treatments are more effective than BT but that the 3 methods are satisfactory for tenderisation of beef for production of re-formed steaks. Reduced redness and higher bacterial numbers arising from VP could render this treatment more suitable for re-formed steaks for catering than for retail sale. A supplementary trial showed that slices from roasted VP-treated re-formed joints(as distinct from grill-cooked steaks tested in the main trial) were better in sliceability and equal to or better in sensory quality than those from commercial whole-muscle round roasts purchased in a supermarket.     

The tenderisation of shin beef using a citrus juice marinade

The effectiveness of organic acids (acetic, citric, lactic) and a citrus juice marinade as tenderising agents in shin beef muscle was investigated. At 0.2 M, citric acid was more effective as a tenderising agent than acetic or lactic acid. Immersion of shin beef strips in citric acid (0-0.05 M) showed that a significant tenderising effect was obtained above a concentration of 0.013 M. When shin beef strips were immersed in the citrus juice marinade (31% orange juice, 31% lemon juice, 38% distilled water) mean pH decreased from 5.7 to 3.1 and mean sample weight increased by ～65%. The mean Warner-Bratzler shear force value decreased from 178 to 44 N cm(-2) following marination while mean sensory analysis scores for tenderness and juiciness increased following marination. A mean total collagen content of 1.4 g/100 g was recorded in shin beef of which 9% was soluble in unmarinated samples and 29% was soluble in marinated samples. The results indicated that the tenderisation of beef samples using a citrus juice marinade could be attributed to marinade uptake by muscle proteins and also to solubilisation of collagen.     

Singular and combined effects of electrical stimulation, post-mortem ageing and blade tenderisation on the palatability attributes of beef from young bulls

Thirty Santa Gertrudis bulls (approximately 15-18 months old) were slaughtered, dressed and split into siides. The right side of each carcass was electrically stimulated (ES) with seventeen impulses (1·8s impulse duration; 1·8s interval between impulses) of 550 V (AC) and 5 A while the left side served as a non-stimulated control (not-ES). At 24h post morten, USDA quality and yield grade data were obtained from each side. On the second day post mortem, all sides were fabricated and strip loins, top sirloin butts and ribeyes were obtained from each side for post-mortem ageing and blade tenderisation studies. Steaks were removed after a post-mortem ageing period of 4 or 18 days and before (not-BT) or after blade tenderisation (BT) for sensory panel evaluations or shear force determinations. ES sides had more youthful lean maturity (P < 0·0001), higher marbling (P < 0.·002), higher USDA quality grades (P < 0·0.0001) and finer-textured lean (P < 0·002) than did not-stimulated (not-ES) sides. ES significantly improved (P < 0·05) palatability traits in two of twenty-four comparisons; BT significantly improved palatability traits in twelve of twenty-four comparisons and 18-day post-mortem ageing significantly improved palatability traits in seven of twelve comparisons. No significant reductions (P < 0·05) in shear force values were observed for steaks from ES versus not-ES sides while significant reductions (P < 0·05) were observed for steaks from BT versus non-BT cuts (four of six comparisons) and for steaks from cuts aged for 18 versus 4 days (ten of twelve comparisons). BT and 18-day post-mortem ageing were more effective for increasing palatability or for decreasing shear force requirements than was ES; however, ES greatly improved lean colour of meat from bulls.     

牛宰后肌肉生物电阻抗与pH值相关性研究

试验在多频(5～200kHz)条件下采用四电极法对30头肉牛宰后背最长肌肉(Longissimusdorsi,LD)的生物电阻抗和pH值进行了为期10d的连续检测。发现肉牛肌肉生物电阻抗同pH值有显著相关性(γ=-1.000～-0.999)。宰后第3天(48h),驱动电流频率为40～200kHz时,肌肉组织生物电阻抗达到最大值,pH值降到最小值。在不同频率下肌肉生物电阻抗表现的离散度不同,尤其是在5～100kHz范围内,肌纤维的生物电阻抗受频率影响较明显,并且和宰后肌肉的贮藏时间有关。在相同的环境条件下,肌肉的横向电阻抗(平行于肌纤维横截面方向)均大于纵向电阻抗(平行于肌纤维方向)。     

Effect of stress-induced high post-mortem pH on protease activity and tenderness of beef

Forty-four Swiss Brown young bulls were stressed by regrouping unfamiliar animals before slaughter. M. longissimus thoracis (6-9th ribs) of carcasses were analysed for post-mortem pH, protease activities (m- and α-calpain, calpastatin and cathepsin B + L), Warner-Bratzler shear force and sensory tenderness and juiciness. Muscles were classified into three groups, according to ultimate pH values: > 6.3, 6.3-5.8 and < 5.8. The most significant difference related to high pH was a higher activity of m-calpain at 7th day post mortem. It was also found that meat showing the highest pH was significantly more tender and juicy. Sensory tenderness was highly correlated with activity of m-calpain at 7th day post mortem (r = 0.776) and with ultimate pH (r = 0.708). It is concluded that high ultimate pH induced by stress significantly increases m-calpain activity, and this results in a greatly enhanced tenderisation of beef meat.     

Assessment of the relationship between chemical components and palatability of major beef muscles and muscle groups

The relationships of chemical components to palatability attributes in 33 different muscles and muscle groups from 25 Canada AA steer carcasses were assessed. Intramuscular fat and moisture accounted for 38.4 and 23.0% of the variation in panel juiciness ratings of all 33 muscles or muscle groups. Insoluble hydroxyproline content was more closely related with palatability attributes than either total or soluble hydroxyproline content, and accounted for 16.8, 26.0, 34.8, 24.0 and 34.8% of the variation in initial and overall tenderness, amount of perceived connective tissue, flavour desirability, and overall palatability, respectively, of all muscles. Exclusion of "sheet-like" support muscles improved the amount of variation accounted for in palatability traits slightly and exclusion of "combination cuts" containing two or more muscles improved the amount of variation accounted for in palatability traits significantly. Insoluble hydroxyproline not only adversely influenced textural properties contributing to tenderness, but also adversely influenced flavour desirability. The amount perceived connective tissue provides a reliable indication of the amount of insoluble hydroxyproline, and vice versa particularly in individual muscles, where the epimysium has been removed.     

The intracellular distribution of small heat shock proteins in post-mortem beef is determined by ultimate pH

This study analysed Longissimus dorsi muscles from 39 Angus or Angus×Limousin bulls to determine the small heat shock protein (sHSP) dynamics in beef aged at 15°C. Using quantitative ELISA we determined that alpha β-crystallin and HSP20 were present at higher levels in muscles from Angus bulls. sHSP levels peaked at 0.5 and 3h post-mortem for HSP20 and alpha β-crystallin respectively. Intermediate pH (pH 5.7-6.3) beef had the highest level of alpha β-crystallin expression at 3-6h post-mortem. Low pH (<5.7) meat had no detected soluble alpha β-crystallin and had diminished HSP27 at 22h post-mortem. The transition of sHSP between a soluble to an insoluble phase was demonstrated by pH titration of a sarcoplasmic fraction. The effect of ultimate pH upon sHSP distribution in post-mortem muscle may influence final meat quality characteristics.     

An investigation of ultimate pH in the muscles of commercial beef carcasses

Ultimate pH values were recorded in the carcasses of steers and heifers at a beef slaughtering plant over a period of 3 years. The incidence of carcasses with a pH_u ≥ 6·0 in the LD—a value usually associated with ‘dark-cutting’ in beef—was 3·2%. A pronounced seasonal effect was observed with the incidence rising from 1·2% for the period February to August to 5·2% for the period September to January, inclusive. An examination of thirteen muscles showed that increases in pH_u above normal values occurred most frequently in the LD and four large muscles of the hindquarter and were much less frequently observed in the eight other hind- and forequarter muscles examined. In the carcasses of young bulls, also slaughtered under commercial conditions, high pH_u values were predominantly associated with the same muscles as in steers and heifers. However, when experimental cattle were given adrenaline to induced high pH_u values, this treatment resulted in a general increase in pH_u in all the muscles examined. The different pattern of pH_u elevation in the adrenaline-treated and commercial carcasses suggests different physiological mechanisms in the two cases.     

The effects of early post-mortem pH and ultimate pH on level and amount of destructured zones in cooked cured hams

Effects of early (1 h p.m. and 3 h p.m.) and ultimate pH (24 h p.m.) on level and amount of destructured zones in cooked cured hams were evaluated. In experiment 1, electrically stimulated (50 V, 14 Hz, 2 × 90 s) and non-stimulated carcass halves, both in combination with two cooling procedures (2 °C from 30 min p.m. vs. 120 min p.m.) resulted in 1.5–35.2 g/kg destructured zones in silversides and 58.4–120.0 g/kg destructured zones in topsides. A high temperature 1 h p.m. in silversides (P = 0.067) and topsides (P = 0.054) was identified as the most important predictor for the defect. In experiment 2, cooked cured hams from topsides selected according to ultimate pH groups (pH < 5.5, pH 5.5–5.7, pH > 5.7) showed between 12.3 and 61.8 g/kg destructured zones. Ultimate pH was specified as most important, however, statistically still not significant (P = 0.135) predictor for the defect. Chemical analysis resulted in low crude ash and high dry matter content as being characteristic for the defect.     

Further investigations into the relationship between ultimate pH and tenderness for beef samples from bulls and steers

Samples of longissimus dorsi muscle from 150 cattle comprising Friesian bulls and steers and Charolais × Angus cross steers, were used to investigate the nature of the relationship between ultimate pH and beef tenderness under conditions where cold-shortening was avoided. A modified Warner-Bratzler (WB) shear machine with a square- rather than a vee-blade enabled several aspects of tenderness to be evaluated, including peak force (PF), initial yield force (IY), PF-IY, and an index of total work done. The two steer groups differed little in meat quality characteristics, but, in terms of six major hindquarter cuts, the Charolais cross group yielded 14·3% more meat per unit live weight, due to a combination of a superior dressing-out percent and a higher cutability. Relative to Friesian steers, the bulls produced beef with a higher ultimate pH (P < 0·001), and after adjustment to a common pH, the bull beef was tougher for all WB parameters except PF-IY. Cooking loss was higher for beef from bulls after adjustment for pH. Although reduced by pH adjustment, beef from bulls remained significantly darker than that from steers (P < 0·05) based on reflectance measurements. Maximum toughness in terms of PF, IY, and work index was at an ultimate pH of 6·0-6·1, but the peak was much less clear for PF-IY. The decline in tenderness with an increase in ultimate pH to 6·2 was associated with a decrease in sarcomere length. This result supports a previous suggestion that shortening explains, at least in part, the lower average tenderness at intermediate pH values.     

Effect of muscle and post-mortem rate of pH and temperature fall on antioxidant enzyme activities in beef

The aim of this study was to investigate the effect of muscle, inner and outer Musculus biceps femoris (IBF and OBF respectively) and Musculus longissimus dorsi (LD), on the post-mortem rate of pH and temperature fall, and the activity of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) during simulated retail display. At day 0 of display (2 days post-mortem), the CAT and GSH-Px activities were lower in IBF than in OBF and LD (P < 0.001), and the SOD activity was lower in OBF compared to IBF and LD (P < 0.001). At day 10 of display, SOD and CAT activities had decreased in all three muscles compared to day 0 (P < 0.001), whereas the GSH-Px activity did increase with time of display. Across muscles, there were significant relationships between temperature fall, colour, lipid and colour stability and antioxidant enzyme activities.     

Variation in the response to manipulation of post-mortem glycolysis in beef muscles by low-voltage electrical stimulation and conditioning temperature

The aim of this study was to investigate how manipulation of glycolytic rate by post-mortem processing conditions influences quality of aged beef of two bovine muscles of different physiological character, longissimus dorsi (LD) and adductor (AD). Post-mortem glycolysis was manipulated by low-voltage electrical stimulation (LV-ES) of half carcasses and by chilling rate of the muscles. Multivariate statistical analysis was used to visualise the data, while ANOVA was used to identify significant effects and interactions. As expected there was a significant effect of LV-ES on the pH decline in the first hours post-mortem in both muscles. Moreover, significant effects of LV-ES on WB shear force measured 2 and 8 days after slaughter were observed for LD at both chilling temperatures, while for AD no effect on WB shear force was observed. Furthermore, the results revealed a large individual variation in the response of LV-ES on both pH decline and WB shear force, and this variation did not always correlate for the two responses. Some animals showed no response of LV-ES on pH decline, but still had an improved WB shear force, and vice versa. The results from this study indicate that there probably are other mechanisms than accelerated pH decline and prevention of cold-shortening, by which LV-ES can affect meat tenderness.     

Predicting longissimus dorsi texture characteristics in beef based on early post-mortem colour measurements

Sixty young bulls of Pirenaica breed that were representative of the beef production and marketing systems in Northern Spain were studied. The following parameters were determined with the aim of predicting beef texture characteristics of the longissimus dorsi based on the objective measurements taken on the carcass at the early post-mortem period: colour measurement (CIE L(?)a(?)b(?)) readings were taken on the latissimus dorsi (LTD), rectus abdominis (RA), and longissimus dorsi (LD) muscles. In this study, it was observed that more information on beef tenderness is obtained with colour measurements taken on the carcass LTD and RA, and LD at 24h post-mortem. However, the regression analysis showed that beef TI from Pireanica young bulls can be predicted quite accurately by C(?) measured on the RA muscle just 45min after slaughter.