Autoxidation of purified myoglobin from two bovine muscles

To elucidate the behavioural differences between beef muscles from the viewpoint of colour stability, oxymyoglobin was extracted at 2 h post mortem, purified from two different muscles (longissimus lumborum (LL), stable and psoas major (PM), unstable) and the autoxidation rate was measured. Oxymyoglobin was isolated after separation from metmyoglobin by chromatography on DEAE-Sepharose and TSK SW 2000 columns, and its purity was controlled by electrophoresis and IEF. Over a wide range of pH values (5-9), temperatures (20-50°C) and ionic strength (0-500 mM), no difference was noted between autoxidation rates of LL and PM oxymyoglobin extracted at 2 h post mortem. Conversely, when myoglobin was extracted at 192 h post mortem, the autoxidation rate of PM oxymyoglobin was higher than LL myoglobin, particularly at elevated temperatures. These differences in autoxidation rates after extraction of myoglobin at 2h and 192 h post mortem were not associated with differences in Ea (approximately 23 kcal/mol).     

Antioxidant enzyme activities in beef in relation to oxidation of lipid and myoglobin

Lipid- and oxy-free radical generation has been implicated in oxidative processes which occur during meat maturation but the importance of the antioxidant enzyme (AOE) activity in these processes is not known. It was shown that metmyoglobin (MetMb) % and lipofuscin content were higher in colour-unstable muscles such as psoas major (PM) and diaphragma (D) compared to longissimus lumborum (LL) and tensor fasciae latae (TFL). Although Superoxide dismutase (SOD) activity is higher post mortem in PM and D muscles than in LL and TFL muscles, catalase and glutathione peroxidase (GPx) activities were higher only in D muscle. The higher AOE activity in colour-unstable muscles such as PM and D was not sufficient to prevent increased formation of MetMb and lipofuscin in these muscles compared to LL and TFL muscles.     

Effects of halothane genotype and pre-slaughter treatment on pig meat quality. Part 1. Post mortem metabolism, meat quality indicators and sensory traits of m. Longissimus lumborum

Forty-eight castrated F₂ offspring of Piétrain and Large White pigs were allocated to a 3 × 2 factorial design in order to study the interactive effect of halothane genotype (NN, Nn and nn) and pre-slaughter treatment [referred to as ‘Experimental’ (EXP) and ‘Commercial-like’ (COL) conditions; the latter combining short transportation, mixing unfamiliar pigs and slaughtering shortly after transport] on muscle post mortem changes and meat quality. The pigs were slaughtered over 4 days. Pre-slaughter glycogen depletion in M. longissimus lumborum (LL) was greater in the nn pigs, compared with the two other genotypes. Lactate accumulation post mortem in LL muscle was greater and the pH value at 40 min post mortem was lower in nn compared with NN pigs. Nn pigs were close to nn pigs for lactate accumulation and showed intermediate pH values in the LL muscle. In the M. semimembranosus (SM), NN and Nn pigs showed the same rate of post mortem changes, as evidenced by similar glycogen, lactate, creatine phosphate and ATP levels, and pH values at 40 min post mortem. Pre-slaughter treatment did not affect the rate of post mortem changes in both muscles and no interactive effect with halothane genotype was found. The pigs slaughtered under the ‘COL’ conditions had a significantly higher ultimate pH in the LL and SM muscles than those slaughtered under the ‘EXP’ conditions. The LL muscle from nn pigs was paler (higher L*) than that of NN and Nn pigs. In SM muscle, Nn pigs showed a significantly higher L* value than NN pigs. Drip loss of the LL muscle was significantly higher in nn compared with NN pigs, the heterozygous pigs being intermediate. Sensory evaluation of the LL muscle showed that nn pigs had a lower colour intensity and colour homogeneity of raw meat than NN and Nn pigs. Tenderness was significantly lower in nn compared with NN pigs, the Nn pigs being intermediate. Pre-slaughter treatment significantly increased ultimate pH in both muscles (LL and SM) but did not affect significantly the rate of pH fall (pH₄₀). It did not affect any of the meat quality traits and no interactive effect with halothane genotype was found. These results confirmed the influence of the halothane gene on the kinetics of muscle post mortem changes and related meat quality traits. They also confirmed the intermediate position of heterozygous pigs in terms of meat quality.     

Effect of dietary vitamin E supplementation on pork quality

The purpose of this experiment was to examine the effect of dietary vitamin E supplementation on pork quality, and in particular on colour stability. Crossbred pigs (n = 72) at a mean weight of 44 kg were assigned to one of two treatments. One group received, during a period of 84 days prior to slaughter, a tapioca based diet, which contained 8 mg vitamin E per kg feed. The other group received during this period the same diet, except it was supplemented with 200 mg vitamin E per kg feed. Muscle samples of longissimus thoracis and lumborum (LL) and psoas (PM) were collected at 24 hr post mortem and meat quality was assessed: pH, drip and cooking loss, shear force and intramuscular fat content. Colour stability was evaluated in fresh muscle (LL and PM) and after freezing (LL only) by measuring redness (a(?)-values) during 6 days of storage at 7 °C. TBA-values and microbiological counts were also determined during storage. Results showed that extra dietary vitamin E had no effect on pig performance (daily gain, feed efficiency, lean meat percentage) nor on meat quality traits. The vitamin E levels were five times higher in the muscles of the treated group than the control group. In comparison with fresh LL muscle, colour stability was lower in PM and after freezing. In both muscles, the vitamin E treatment reduced TBA-values, in particular after frozen storage. No effect was found on microbiological counts. Colour stability was improved in LL after 6 days of storage, but not in PM. The effect in LL is too late to be of practical significance, since pork is usually sold well before that time in The Netherlands. It is suggested that variation in feedstuff composition of the diet may possibly explain part of the variable results reported in literature for the effect of vitamin E supplementation on colour stability of pork.     

Occurrence of giant myofibres according to muscle type, pre- or post-rigor state and genetic background in turkeys

Forty-five male turkeys were bred to 15 weeks of age. At this age, the birds weighed 4, 6 and 8 kg depending on their genetic origin. At 3 min and 24 h post mortem samples from the pectoralis major (PM) and iliotibialis lateralis (ITL) muscles were excised for biochemical and histochemical measurements. At 3 min post mortem, except in the size of the myofibres, no differences in types, shapes or luminance due to glycogen was seen between the three lines in the respective muscles. Birds from the fast growing line had bigger muscle fibres than the two other lines, but the muscles did not present more glycolytic or oxidative enzyme activities. No muscle abnormalities were noticed at this stage. At 24 h post mortem, the presence of giant fibres (GF) was seen which differed proportions according to muscle and in genetic background. The GF were found both in the fast (PM) or mixed type (ITL) muscles. In this latter muscle they were more prevalent in the slow contracting muscle fibres than the other fiber types. It was concluded that the occurrence of the GF is independent of the genetic background of the birds or the type of muscle, but is dependent on the biochemical events occurring during rigor mortis.     

The significance of pre-slaughter stress and diet on colour and colour stability of pork

The influence of pre-slaughter stress and a diet known to affect post mortem muscle metabolism or a standard diet (control pigs) on colour and colour stability of m. longissimus dorsi, m. biceps femoris and m. semimembranosus from 112 female pigs, free of the Halothane gene, was investigated. Pre-slaughter stress increased the early post mortem temperature in the three muscles, as well as the pH decline in control pigs, but not in pigs fed the experimental diet. Colour was measured on sliced samples after 0, 2 and 5 days retail display (1, 3 and 6 days post mortem, respectively) from the three muscles aged 1 day before cutting as well as on sliced m. longissimus dorsi samples aged 8 days before cutting (8, 10 and 13 days post mortem, respectively). Early post mortem pH was not a main determinant of the colour and colour stability, while the degree of pre-slaughter stress and especially its influence on temperature early post mortem was crucial in relation to colour development and colour stability. The discoloration rate was enhanced in m. longissimus dorsi aged for 8 days prior to retail display compared with samples aged for 1 day. However, the extent of the discoloration after 5 days of retail display was not inferior in muscle samples aged for 8 days due to a higher degree of blooming. Finally, present data indicate that 3-4 days ageing of pork prior to retail display results in the optimal colour stability.     

Raman spectroscopy compared against traditional predictors of shear force in lamb m. longissimus lumborum

A Raman spectroscopic hand held device was used to predict shear force (SF) of 80 fresh lamb m. longissimus lumborum (LL) at 1 and 5 days post mortem (PM). Traditional predictors of SF including sarcomere length (SL), particle size (PS), cooking loss (CL), percentage myofibrillar breaks and pH were also measured. SF values were regressed against Raman spectra using partial least squares regression and against the traditional predictors using linear regression. The best prediction of shear force values used spectra at 1 day PM to predict shear force at 1 day which gave a root mean square error of prediction (RMSEP) of 13.6 (Null = 14.0) and the R² between observed and cross validated predicted values was 0.06 (R²_cv). Overall, for fresh LL, the predictability SF, by either the Raman hand held probe or traditional predictors was low.     

Early post-mortem conditions and the calpain/calpastatin system in relation to tenderness of double-muscled beef

Early post mortem temperature, pH, sarcomere length, colour, water holding capacity, calpain/calpastatin activities and myofibrillar protein concentrations (semi-quantative SDS-PAGE), measured at different times post mortem on 153 double-muscled Belgian Blue White bulls, were related to shear force (SF) measurements. The M. longissimus thoracis tenderised up to 8 days post mortem. SF was slightly correlated with temperature at 3 h post mortem (r = 0.20, p = 0.015), but not with pH early post mortem. Higher ultimate pH values measured at 24 h post mortem were related to darker meat, lower cooking losses and shorter sarcomere lengths. Sarcomere length was significantly related to SF, even after 12 days of ageing, suggesting that proteolytic activity was not able to overcome shortening. Up to 12 days post mortem, calpastatin and m-calpain activities were significantly correlated with SF suggesting a considerable role of calpains in meat tenderization of double-muscled Belgian Blue White bulls, although at 24 h post mortem, μ-calpain could no longer be detected. Titin, nebulin, filamin and troponin-T were degraded during the ageing period. Troponin-T was degraded by 80% between day 1 and 8. At 8 days post mortem its concentration was significantly correlated with 30 kDa (r = 0.63, p = 0.00), shear force (r = 0.39, p = 0.00), calpastatin activity at 1 day post mortem (r = 0.29, p = 0.01) and with the m-calpain/ calpastatin activity ratio at 1 day post mortem (r = -0.43, p = 0.00).     

The relationship between early post-mortem pH and the tenderisation of beef muscles

The rate of early post-mortem pH fall in bovine muscle was studied to determine its influence on the rate and extent of the tenderisation process. The pH of M. longissimus dorsi (LD) and M. semimembranosus (SM) muscles of Hereford cross Friesian heifers (n = 127) was taken up to 24 h post mortem. Twenty-four LD and 24 SM muscles were selected according to their rate of pH fall; slow (n = 8), intermediate (n = 8) and fast (n = 8) and were sampled at 2, 7 and 14 days post mortem for sensory, mechanical, physicochemical and biochemical analysis. Fast glycolysing LD muscles were rated more tender in sensory analysis and texture assessment whereas slow glycolysing muscles were considered significantly tougher (p < 0.001). Fast glycolysing LD had a significantly lower shear force (p < 0.001) at each stage of ageing. Slow glycolysing LD and SM had the highest shear force values. No significant difference was found in intramuscular fat or moisture content between the groups. Slow glycolysing LD muscles had shorter sarcomere lengths at 2 days post mortem. SDS-PAGE electrophoresis patterns showed increased proteolysis, such as the earlier appearance of the 30 kDa fragment, which is believed to be a good indicator of tenderness, in fast glycolysing muscle. These results suggest that the rate of post-mortem pH fall plays an important role in proteolysis and tenderisation.     

Dietary vitamin E effect on color stability and sensory assessment of spoilage in three beef muscles

Effects of dietary vitamin E supplementation (1204 IU/head/day) for 122 days on color stability and microbial load on beef m. longissimus lumborum (LL), m. gluteus medius (GM) and m. psoas major (PM) were studied by subjective and objective evaluation. Color stability of these muscles followed the order LL > GM > PM (p < 0.05). Vitamin E-treated LL, GM and PM showed less metmyoglobin formation, higher a^* values and lower hue angle values than controls during storage at 4 °C (p < 0.05). Sensory evaluation demonstrated that panelists preferred the appearance of vitamin E-treated LL, GM and PM beef steaks. Vitamin E supplementation did not affect total microbial load on LL, PM and GM and did not influence panelists' olfactory assessment of microbial spoilage of beef. Endogenous -tocopherol concentration and lipid stability of microsomal fractions of LL, GM and PM were greater (p < 0.05) in vitamin E-treated muscles relative to controls. There was no muscle effect on the pro-oxidant activity of microsomes towards oxymyoglobin oxidation (p > 0.05). Oxymyoglobin stability was greater in the presence of microsomal fractions obtained from vitamin E-treated muscle than in those from controls. Dietary vitamin E supplementation delayed oxymyoglobin oxidation in LL, PM and GM muscle and increased the color shelf-life of these muscles without affecting total microbial load.     

Effects of pithing on pH, creatine phosphate and ATP-related compounds of beef Psoas major and Longissimus dorsi muscles

The effects of pithing at slaughter on meat quality were studied in M. longissimus dorsi (LD muscle) and M. psoas major (PM muscle) from steers. Ten steers, half of them pithed and the others not pithed at slaughter, were used for determining pH values and concentrations of creatine phosphate (CP), adenosine triphosphate (ATP) and its breakdown products in the muscles at 2·0 h post mortem. CP was not detected in any PM muscles from pithed steers and no significant differences were observed between pithed and non-pithed steers on the mean values of pH and any compounds, but significant differences were observed in the variance of pH value, ATP, (inosine monophosphate IMP) and inosine levels in PM muscles and of (adenosine diphosphate ADP) and IMP levels in LD muscles. When two steers with excitable temperament were excluded from the pithed group significant differences of variance between the treatments were observed only in PM muscles. The pithing procedure thus affects the levels of pH and of some of the ATP-related compounds in the PM but not in LD muscles.     

Thermal transition of collagen in ovine connective tissues

The thermal transition temperature (T(m)) of collagen in a range of muscle and non-muscle connective tissues from lambs, hoggets and mature sheep was measured by differential scanning calorimetry. The muscles selected were: semimembranosus (SM), semitendinosus (ST), biceps femoris (BF), Longissimus dorsi (LD) and psoas major (PM). Although the T(m) of intramuscular SM collagen from an aged ewe underwent no significant change with time post mortem, that of a 5-months-old lamb had dropped by 0·9°C after 2 days at 19°C. The epimysium of each muscle exhibited a higher T(m) than the corresponding intramuscular connective tissue. The LD and BF tendons each had a lower T(m) than corresponding intramuscular connective tissue but this was not true for the PM. Furthermore, the PM tendon generated an isometric tension more than five times that of the LD, BF or psoas minor tendons. This indicates that the PM tendon is richer in heatstable crosslinks than any of the other tendons investigated. In all tissues, except the liver capsule, there was an increase in T(m) with animal age. However, the rate of change T(m) varied from one tissue to another. For example, the SM intramuscular collagen matured at an earlier age than that of other muscles, the PM being slowest to mature. In keeping with the changes in T(m) values, the Warner-Bratzler peak force of ST muscles increased markedly in older sheep, but there was no significant difference in peak force of SM muscles between lambs, hoggets and mature sheep.     

Post-mortem changes in myofibrillar proteins of breast and leg muscles from broilers,spent hens and Taiwanese Country Chickens

Post mortem ageing at 4°C was studied in the breast and leg muscles from broilers, White Leghorn spent hens and Taiwanese Country Chickens (TCC). Purified myofibrils were prepared from muscles after 0, 1, 3, 5, and 7 days of post mortem storage at 4°C. SDS-PAGE was used to examine the changes in myofibrillar proteins of the muscles. Results showed that 30 kDa components appealed earlier in the breast muscles than in the leg muscles and in the order: broiler, TCC, and spent hen. The intensity of 30 kDa band increased with post mortem time. In the breast muscles, a decrease in the intensity of the α-actinin band could be observed at 1 day post mortem in broilers and TCC and at 3 days post mortem in spent hens. This decrease, however, could not be found in the leg samples until 5 or 7 day post mortem. Titin 1 band disappeared within 3 day post mortem in the breast samples but within 5 days in the leg samples. Similar results could be observed in the degradation of nebulin although traces of nebulin remained in the teg muscles of TCC after 7 days post mortem.     

The effect of electrical stimulation on the quality of three bovine muscles

Meat bulls were randomly assigned to five treatment groups-intermittent electrical stimulation at 300 V (ES) at 5 min and 35 min post mortem (intact carcasses), 35 min post mortem (split carcasses) and non-stimulated controls (NS) (intact and split carcasses). Stimulated carcasses in all groups showed a significantly more rapid pH fall during the first 8h post mortem in adductor (AD), longissimus dorsi (LD) and triceps brachii (TB) muscles. Cooling rates were relatively slow. Samples were removed from the carcass at 24h post mortem. After vacuum storage at 3°C for 6 days stimulated muscles showed lower drip (LD and TB) and heating loss (TB), lower shear force values (AD, LD and TB) and higher taste panel scores (AD, LD and TB) compared with NS controls. No significant differences in tenderness were observed between the three ES groups. Sarcomere length assessment showed more contraction in NS carcasses, particularly in the superficially located LD and TB. These results suggest that cold shortening may occur in some muscles under cooling conditions so far considered safe in this respect. Since higher drip losses coincided with lower sarcomere lengths in these (NS) muscles, it is suggested that, under these conditions, ES may mask the increased drip losses which are possibly the result of muscle contraction. Furthermore, ES prevents the occurrence of cold shortening and, in addition, may exert some 'extra tenderising effect', which is not related to splitting of the carcass nor restricted merely to the LD muscle.     

Comparative study of low-field NMR relaxation measurements and two traditional methods in the determination of water holding capacity of pork

The correlation between transverse relaxation, T(2,) and water holding capacity (WHC) determined either by Honikels bag method (Honikel, 1998) or centrifugation has been investigated in meat samples from m. longissimus dorsi (LD) 24 h post mortem from 74 pigs. Bi-exponential analysis of the transverse relaxation, T(2), showed highly significant correlations between both the two NMR time constants (T(21),T(22)) and water holding capacity determined by both Honikels bag method (r(T(21))=-0.72 and r(T(22))=0.77) and centrifugation (r(T(21))-0.50 and r(T(22))=0.75). This shows that transverse relaxation measurement is an efficient method for determination of water holding capacity in pork. Significant correlations were also found between T(21) and T(22) measured 24 h post mortem and pH measured at various time post mortem. This indicates that transverse relaxation, T(2), reflects pH-induced structural changes occurring in muscles post mortem.     

Low voltage electrical stimulation of lamb carcasses: effects on meat quality

The effects of an early post mortem low voltage electrical stimulation (28 V, 60 Hz) on biochemical changes and on final tenderness in muscles Longissimus thoracis et lumborum and Semimembranosus from lamb carcasses were studied. It was shown that electrical stimulation accelerated the glycolytic process resulting in a significant fall in pH during the first 6 h post mortem in both muscles examined and in a significant reduction in adenosine triphosphate (ATP) content in muscle Longissimus thoracis et lumborum. The effect of electrical stimulation on tenderness was recorded by measuring shear force values 2 and 7 days post mortem. Tenderness was significantly improved by electrical stimulation for the Longissimus thoracis et lumborum both at 2 and at 7 days post mortem, while for Semimembranosus electrical stimulation significantly increased tenderness just at 7 days post mortem.     

The effect of high and low voltage electrical stimulation on beef quality

Meat bulls were assigned to three treatment groups—high voltage intermittent electrical stimulation, low voltage electrical stimulation and no stimulation.Both stimulation methods resulted in a significantly more rapid pH fall in the longissimus and adductor muscles during the first 8 h post mortem. Carcass cooling rates were relatively slow, since temperatures of the longissimus and adductor muscles were 15°C, respectively, at 8 h post mortem.Samples of stimulated longissimus, cut at 24h post mortem and vacuum stored at 3°C for 6 days, had a brighter red colour, higher drip and heating loss, lower shear force values and scored better in taste panels, compared with samples from control carcasses. No significant differences were observed between high and low voltage electrical stimulation in quality traits measured.Although the combined result of pH and temperature measurements during the first 8 h post mortem suggest an absence of cold shortening conditions in control carcasses, a lower sarcomere length was found in samples of the longissimus muscle taken from these carcasses at 24 h post mortem.     

Effects of stress and high voltage electrical stimulation on tenderness of lamb m. longissimus

This study was conducted to investigate the reported effect of pre-slaughter stress on meat tenderness independent from its effect on ultimate pH, and its interaction with electrical stimulation. From a group of 80 Coopworth lamb, 40 were stressed by subjecting the animals to a swim wash 3 h before slaughter and the use of dogs to assemble the animals to the access ramp of the abbatoir. Half of the carcasses of each group was electrically stimulated within 30 min post mortem. Temperature and pH decline of the longissimus was monitored and shear force of the cooked muscle was determined at 2 days post mortem and after 6 weeks vacuum storage at 1°C. To investigate an effect of stress independent of ultimate pH, 10 muscles with an ultimate pH below 5.8 were selected from each group for detailed analysis. This analysis consisted of determination of calpastatin activity and sarcomere length, and immunoblotting of μ-calpain and calpain substrates. The stress treatment led to an increase in the number of muscles with an ultimate pH above 5.8 (32.5 vs 15%), and muscles with an ultimate pH above 5.8 were significantly tougher than muscles with an ultimate pH below 5.8 at 2 days post mortem. Electrical stimulation improved tenderness at two days post mortem. This effect could be attributed to an effect on muscle contraction, but not on post mortem proteolysis of calpain substrates. A large variation in tenderness at 2 days post mortem was observed and this was not reduced by electrical stimulation. Six weeks of vacuum storage resulted in a 6 kgF drop in mean shear force and a uniformly tender product. Despite the fact that the stress treatment was similar to those in earlier studies, we failed to observe an effect of stress independent of ultimate pH on tenderness. The reason for this is unclear, but differences in the response to stress between breeds may be responsible. The results of the present study underscore the importance of minimizing pre-slaughter stress and adequate post mortem storage for meat quality.     

牛不同部位肌肉高铁肌红蛋白还原酶活力及耗氧率对肉色稳定性的影响

为了研究牛不同部位肌肉的高铁肌红蛋白还原酶活力(MRA)和肉的呼吸耗氧强弱对肉色泽稳定性的影响,本文以牛的三个部位的肌肉:背最长肌(LL)、半腱肌(ST)、腰大肌(PM)为研究对象,4℃避光贮藏5d,测定MRA、肌红蛋白(MMb)含量、耗氧率(OCR)等,探究肉色稳定性与牛肉部位、MRA和呼吸耗氧率之间的关系。结果表明,三种肌肉中,背最长肌的色泽稳定性最好,腰大肌最差,半腱肌介于中间;MRA越高的肌肉,肉色越稳定;OCR越低的肌肉,肉色越稳定。      

Changes in solubility and enzymic activity of muscle glycogen phosphorylase in PSE-muscles

Comparison of the crude extracts of soluble proteins of PSE (pale, soft and exudative) and normal porcine muscles shows that the solubility and activity of muscle glycogen phosphorylase are diminished in PSE muscles. In the insoluble fractions of the muscle extract, however, an increased amount of a protein with the molecular weight of the phosphorylase subunit (92·500-95·000) can be found by means of SDS-electrophoresis. The PSE conditions with high temperatures of 36-40°C in the first hour post mortem and a low pH of 5·3-5·8 at the same time post mortem are simulated with normal porcine muscles at twenty-four hours post mortem which causes the same change in solubility and activity of muscle glycogen phosphorylase as in PSE muscles. This proves, for the first time, that low pH and high temperature in whole muscles cause a denaturation of phosphorylase, as indicated by both reduced activity and decreased solubility. Previous studies have looked only at one of these aspects. This supports the hypothesis of Bendall & Wismer-Pedersen (1962) that in PSE muscles a partial denaturation of sarcoplasmic protein occurs.