RELATION BETWEEN ISOMETRIC TENSION, POSTMORTEM pH DECLINE AND TENDERNESS OF POULTRY BREAST MEAT

Postmortem changes in isometric tension, pH and shear force of poultry breast meat were studied to determine the relation between rigor contraction and tenderness. Strips of pectoralis major muscle immersed in isotonic saline solution held at 25°C developed measurable tension when their pH dropped to 6.1–6.3. The tension gradually increased until the pH dropped to a final value of 5.5–5.8, then started to decline. Muscle cooked at the start of tension development had the highest shear force. After that the shear force of the cooked meat gradually declined to a minimum value. The results indicate a high correlation (r=0.97) between ultimate shear force and degree of maximum tension developed during rigor.     

The influence of high temperature, type of muscle and electrical stimulation on the course of rigor, ageing and tenderness of beef muscles

The course of rigor mortis (rigor), ageing and tenderness has been evaluated for three beef muscles; M. biceps femoris (BF), M. semimembranosus (SM) and M. semitendinosus (ST), when entering rigor at constant temperatures of 15 and 37°C respectively, with and without electrical stimulation (ES/NS) (85 V, 14 Hz and 32 s). The course of post-mortem changes has been registered by isometric tension, by shortening of unrestrained muscle strips and by following the pH decline and the changes in metabolites, such as ATP and CP. Ageing at +4°C was recorded by measuring Warner-Bratzler (W-B) shear values 2, 8 and 15 days post mortem. On the last occasion, the sensory properties of the cooked meat were also evaluated. Maximum shortening and isometric tension were higher at 37°C as compared to 15°C, whereas ES did not reduce rigor shortening. A high correlation between maximum shortening and the ATP-level at the onset of the shortening rapid phase was found (r = 0·77(???)), which could explain the greater shortening obtained at 37°C compared to 15°C. Rigor shortening is an important phenomenon governing meat tenderness as tenderness is highly affected by rigor temperature but not by ES. This was the case for muscles SM and ST but not for BF muscle. Even though tenderness was measured after ageing (15 days post mortem), shortening during rigor seems to be more important for toughness when rigor mortis occurs at 37°C than any suggested tenderizing effect due to increased proteolysis in this temperature region.     

Shortening as a factor in meat ageing

Summary. Shortening during the slow and rapid phases of rigor mortis onset determines largely the extent to which beef ages. For meat stored at 15°C for 3 days, shear-force values are uniformly low at shortenings of 0% to 20% of the freshly excised muscle length. However, there is a four- to five-fold increase in toughness as shortenings proceed from 20% to 40%. This is followed by a decline in toughness as shortenings increase further from 40% to 55%. With increasing shortenings beyond 20%, progressive decreases occur in the extent to which meat ages until at 40% shortening, ageing has declined to zero.     

鲢鱼新鲜度对鱼糜凝胶品质的影响

通过对4 ℃条件下鲢鱼死后10 h感官特性、pH值和僵直指数的变化过程以及鲢鱼死后不同时间鱼肉的挥发性盐基氮（total volatile basic nitrogen,TVB-N）值和Ca2＋-ATP酶活性变化的检测,研究鲢鱼肉新鲜度对鱼糜凝胶品质的影响。结果表明：鲢鱼在死后2～3 h开始进入僵直期,鱼体僵直指数升高,pH值下降;随着鲢鱼死后时间的延长,鱼肉的TVB-N值显著升高,Ca2＋-ATP酶活性显著降低。采用死后不同时间的鲢鱼肉制作的鱼糜凝胶,其凝胶强度、保水性和白度均有显著差异,其中以新鲜鲢鱼为原料制作的鱼糜凝胶的凝胶强度最高,而鱼糜凝胶的保水性和白度在鱼肉的僵直期最差。     

The influence of low temperature, type of muscle and electrical stimulation on the course of rigor mortis, ageing and tenderness of beef muscles

The course of rigor mortis, ageing and tenderness have been evaluated for two beef muscles, M. semimembranosus (SM) and M. longissimus dorsi (LD), when entering rigor at constant temperatures in the cold-shortening region (1, 4, 7 and 10°C). The influence of electrical stimulation (ES) was also examined. Post-mortem changes were registered by shortening and isometric tension and by following the decline of pH, ATP and creatine phosphate. The effect of ageing on tenderness was recorded by measuring shear-force (2, 8 and 15 days post mortem) and the sensory properties were assessed 15 days post mortem. It was found that shortening increased with decreasing temperature, resulting in decreased tenderness. Tenderness for LD, but not for SM, was improved by ES at 1 and 4°C, whereas ES did not give rise to any decrease in the degree of shortening during rigor mortis development. This suggests that ES influences tenderization more than it prevents cold-shortening. The samples with a pre-rigor mortis temperature of 1°C could not be tenderized, when stored up to 15 days, whereas this was the case for the muscles entering rigor mortis at the other higher temperatures. The results show that under the conditions used in this study, the course of rigor mortis is more important for the ultimate tenderness than the course of ageing.     

Tracing processes of rigor mortis and subsequent resolution of chicken breast muscle using a texture analyzer

Rigor mortis is an important change affecting meat palatability. However, there seems no efficient way to continuously and automatically track the whole process of rigor mortis and subsequent resolution. This study is to explore a method to realize the traceability of the onset and development of rigor mortis of muscles using a texture analyzer. A penetration analysis was proven feasible to track the changes of muscle within 48 h postmortem. Chicken breasts were penetrated using a 50 mm probe holding until 172,800 s (48 h) immediately after bleeding. The results confirmed that ambient temperature had a significant effect on the process of rigor mortis and its subsequent resolution, that thaw rigor occurred for frozen muscles before rigor, and that struggle at slaughter accelerated the rigor process. The established approach would give us more accurate details on postmortem physicochemical changes in skeletal muscle.     

High and low rigor temperature effects on sheep meat tenderness and ageing

Immediately after electrical stimulation, the paired m. longissimus thoracis et lumborum (LT) of 40 sheep were boned out and wrapped tightly with a polyethylene cling film. One of the paired LT's was chilled in 15°C air to reach a rigor mortis (rigor) temperature of 18°C and the other side was placed in a water bath at 35°C and achieved rigor at this temperature. Wrapping reduced rigor shortening and mimicked meat left on the carcass. After rigor, the meat was aged at 15°C for 0, 8, 26 and 72 h and then frozen. The frozen meat was cooked to 75°C in an 85°C water bath and shear force values obtained from a 1×1 cm cross-section. The shear force values of meat for 18 and 35°C rigor were similar at zero ageing, but as ageing progressed, the 18 rigor meat aged faster and became more tender than meat that went into rigor at 35°C (P<0.001). The mean sarcomere length values of meat samples for 18 and 35°C rigor at each ageing time were significantly different (P<0.001), the samples at 35°C being shorter. When the short sarcomere length values and corresponding shear force values were removed for further data analysis, the shear force values for the 35°C rigor were still significantly greater. Thus the toughness of 35°C meat was not a consequence of muscle shortening and appears to be due to both a faster rate of tenderisation and the meat tenderising to a greater extent at the lower temperature. The cook loss at 35°C rigor (30.5%) was greater than that at 18°C rigor (28.4%) (P<0.01) and the colour Hunter L values were higher at 35°C (P<0.01) compared with 18°C, but there were no significant differences in a or b values.     

Cold shock reactions in iced tropical fish

The development of a rigor mortis-like stiffening and the biochemical changes associated with it were investigated in tilapia ( Oreochromis aureus/niloticus hybrid), a tropical freshwater species, and common carp ( Cyprinus carpio ), a temperate freshwater fish, during storage in ice (0°C) and at ambient temperature (22°C). Onset of stiffening in carp occurred between 16 and 17 hr after death at both temperatures but full stiffness developed much later and was a longer duration at 0°C. In tilapia, onset occurred after 7 hr at 22°C and full stiffness was established after 19 hr. However, at 0°C, tilapia experienced a cold shock reaction such that they stiffened within minutes of being placed in ice and were fully rigid within 8 hr. Resolution of stiffness in this species also occurred later at 0°C. The rate of ATP degradation was similar under both storage conditions in tilapia but more rapid at ambient temperature in carp. Although the rate of lactic acid accumulation was faster at the higher temperature in tilapia, it was not nearly so marked as for carp. Objective measurement of contractions in excised muscle fibres from trout ( Salmo gairdnerii ) and tilapia indicated that reducing the temperature delayed the occurrence of the contraction and reduced its intensity. It was concluded that cold shock stiffening and rigor mortis stiffening are different.     

The influence of temperature on shortening and rigor onset in beef muscle

At sufficient ATP concentration and temperatures below about 15°C, pre-rigor beef muscles (neck muscles) contract; this phenomenon is known as cold shortening. There is also a contracture at higher temperatures occurring just before rigor onset which is called rigor shortening. While rigor shortening starts in neck muscles at pH around 6·3–6·0 and at about 2 μMol ATP/g muscle, cold shortening can begin at pH around 7·0 and the full ATP concentration (4 μMol ATP/g) in the muscle. Shortening can take place as long as there is no irreversible formation of the actomyosin complex in the muscle, i.e. before rigor onset occurs, which can be measured by intermittent loading of the muscle. The degree of extensibility which follows starts to decrease at the moment of rigor onset. This irreversible loss of extensibility at temperatures between the freezing point (?1°C) and physiological temperatures (38°C) starts at various pH values and ATP concentrations in the muscle. At 38°C the rigor onset occurs at pH 6·25 and about 2 μMol ATP/g muscle, dropping at 15°C to pH 5·75 and 1 μMol ATP/g muscle. At 0°C, as at all temperatures below 10°C, the loss of extensibility at medium loads (about 250 g/cm²) begins shortly after cold shortening. This loss of extensibility is reversible by increasing the load or raising the temperature. The irreversible loss, or rigor onset, however, occurs at 0°C with pH of 6·1–6·2 and 1·8–2·0 μMol ATP/g muscle. Thus, the onset of rigor is influenced by more than one factor. Temperature, pH and ATP concentration each play a rôle.Maximum loss of extensibility or completion of rigor is reached between 10°C and 38°C at pH 5·5–5·6 and less than 0·5 μMol ATP/g muscle. At 0°C the completion of rigor takes place at pH 6·0, but still at 0·5 μMol ATP/g muscle. The latter fact shows that the completion of rigor is solely dependent on the ATP concentration in the muscle; nevertheless, the pH of rigor completion is higher in the extreme cold shortening range. This is apparently due to a different pH/ATP relationship in muscles at low temperatures.The results are discussed in terms of changes in the concentration of Ca²⁺ ions and ATP.The results are of particular interest for the handling of hot-boned meat; that is, for both the cooling of pre-rigor muscle and the use of hot-boned meat for processing.     

Biochemical and technological characteristics of hot chicken meat

In the hot breast and leg muscles of broiler chicken the level of ATP, the 'R' value, the lactic acid content, the pH value, the length of sarcomers, the water and fat retention capacity, the fat emulsion stability, thermal drip, and the extractability of protein fraction were investigated. It was found that in the breast muscles the onset of rigor mortis commenced within 30–60 min, and in the leg muscles as early as 15–30 min after killing of the birds. The deepest rigor mortis occurred between the first and fourth hour, and then gradually declined, sooner in the leg than in the breast muscles. The addition of sodium chloride (2.0–2.5%) to the minced pre-rigor meat not later than 40 min after slaughter, or better, an injection of NaCl brine into intact muscles 15 min after slaughter of birds, preserved their good technological properties.
The tenderness and the thermal drip of hot salted and chilled salted muscles showed no significant differences, but water retention and fat emulsifying capacity were better in the hot salted meat samples. The hot salted and cooked muscles were preferred by the sensory panel to corresponding samples of chilled muscles.
From the hot salted chicken meat more sarcoplasmic and myofibrillar proteins were extracted than from meat salted after chilling. However, after frozen storage the extractability of myofibrillar proteins were higher in the salted chilled meat.     

贮藏温度对兔肉品质变化的影响

把刚宰后的兔肉放在4、15和25℃3种不同的温度条件下贮藏,连续分析测定宰后兔内在不同温度贮藏条件下的各种理化和微生物指标的变化,结果表明:不同温度对兔肉在贮藏过程中pH值、滴水损失、挥发性盐基氮、TBARS值和微生物指标都有显著影响(P<0.05)。贮藏的温度高,兔肉中pH值回升的时间短、滴水损失大、挥发性盐基氮的含量高、微生物繁殖的速度快,与低温(4℃)条件下贮藏的兔肉比较,其品质变劣的速度快;温度影响兔肉的颜色,兔肉的贮藏温度越高,兔肉的氧化速度就会加快,导致兔肉α~*值下降、L~*值增加,颜色变浅。而低温贮藏兔肉(4℃)条件下,兔肉颜色维持的时间比较长久,同时低温也抑制了兔肉的氧化作用,TBARS值较小;宰后兔肉的嫩度呈开始下降,随后逐渐上升的趋势,不同的温度处理,对于兔肉僵直后的嫩化作用影响显著(P<0.05);中温(15℃)和高温(25℃)贮藏条件下的兔肉成熟速度快,低温(4℃)贮藏兔肉经历缓慢排酸后,品质好;在4℃条件下的兔肉即冷却肉货架期比较长,可以保存6d,15℃条件下3d,而25℃条件下只能保存ld。综合考虑,低温(4℃)条件下贮藏兔肉比较合理。     

PSE-LIKE SYNDROME IN BREAST MUSCLE OF DOMESTIC TURKEYS: A REVIEW

There are several similarities between the development of pale, soft, exudative (PSE) meat in breast muscle (Pectoralis supeficialis) of domestic turkeys, swine longissimus and ham muscles. Although the ultimate cause of the syndrome is not known, it appears that the combination of antemortem stress sensitivity of the domestic turkey and predominantly glycolytic metabolism of the breast muscle, results in accelerated rigor mortis processes. The consequent low pH (<5.8) combined with high breast muscle temperature (>35C), typically causes protein denaturation leading to soft and discolored, PSE meat with reduced protein functionality. Our studies revealed that phosphorylase, a sarcoplasmic enzyme, becomes denatured and tightly associated with the myofibrils in PSE turkey breast     

Influence of Postmortem Changes in Bovine Muscle on the Water-Holding Capacity of Beef. Postmortem Storage of Muscle at Various Temperatures Between 0 and 30°C

Bovine neck muscles were incubated between 0° and 30°C soon after slaughter. At different times postmortem biochemical and physical parameters and cooking loss in homogenates with or without salt were measured. The rate of pH fall in muscle depends on the incubation temperature. At 0.5°C the pH drops fast at first, leveling off afterwards but between 7° and 14°C there is an initial lag period of 2-3 hr. At 30°C no lag phase occurs. The increased rate of postmortem metabolism at 0.5°C is accompanied by cold shortening which occurs before onset of rigor and is followed by little rigor shortening. Above 16°C rigor shortening increases with rising temperature without prerigor contraction. Neither shortening nor development of rigor have an immediate influence of WHC of muscle and unsalted muscle homogenates; the small decrease of WHC postmortem is due to pH fall only and independent of temperature. Salted homogenates prepared from muscles at different time postmortem show above pH 6.0 a similar relationship between pH and WHC. At the onset of rigor mortis (pH 5.9), however, the WHC of the salted homogenate decreases strongly. The practical consequences of these results with regard to processing of beef are discussed.     

Effect of muscle restraint on sheep meat tenderness with rigor mortis at 18°C

The effect on shear force of skeletal restraint and removing muscles from lamb m. longissimus thoracis et lumborum (LT) immediately after slaughter and electrical stimulation was undertaken at a rigor temperature of 18°C (n=15). The temperature of 18°C was achieved through chilling of electrically stimulated sheep carcasses in air at 12°C, air flow 1-1.5 ms(-2). In other groups, the muscle was removed at 2.5 h post-mortem and either wrapped or left non-wrapped before being placed back on the carcass to follow carcass cooling regimes. Following rigor mortis, the meat was aged for 0, 16, 40 and 65 h at 15°C and frozen. For the non-stimulated samples, the meat was aged for 0, 12, 36 and 60 h before being frozen. The frozen meat was cooked to 75°C in an 85°C water bath and shear force values obtained from a 1 × 1 cm cross-section. Commencement of ageing was considered to take place at rigor mortis and this was taken as zero aged meat. There were no significant differences in the rate of tenderisation and initial shear force for all treatments. The 23% cook loss was similar for all wrapped and non-wrapped situations and the values decreased slightly with longer ageing durations. Wrapping was shown to mimic meat left intact on the carcass, as it prevented significant prerigor shortening. Such techniques allows muscles to be removed and placed in a controlled temperature environment to enable precise studies of ageing processes.     

POSTMORTEM SHORTENING OF LAMB LONGISSIMUS OXIDATIVE AND GLYCOLYTIC FIBERS

Percentages of lamb M. longissimus thoracis et lumborum fiber types were approximately 66 oxidative and 34 nonoxidative, without significant differences among muscle regions. The effects of skeletal restraint and muscle region on sarcomere shortening during rigor development were found to be highly significant; sarcomeres of caudal-ventral location were stretched by skeletal restraint while the rest were all shortened. In excised muscles, both fiber type and postmortem temperature exerted a highly significant effect on sarcomere shortening. Oxidative fibers showed a more intense shortening, already evident at temperatures well above those causing cold shortening. While shortening of glycolytic fibers was gradually more intense as treatment temperature decreased from 20 to 0°C, a maximum contraction of about 40% was reached at 15°C in oxidative fibers and lower temperatures did not cause any further shortening. Average fiber shortening was found to be highly correlated to meat toughening.     

The effect of post-mortem conditions on the extractability and adenosine triphosphatase activity of myofibrillar proteins of rabbit muscle

Summary. 1. Washed myofibrils from rabbit muscle have been heated at pH values between 4.8 and 5.6 and temperatures between 35°C and 42°C. It has been found that, under these conditions, myofibrils lose their Ca²⁺ activated adenosine triphosphatase, their Mg²⁺ activated adenosine triphosphatase and also become less extractable in M KCl–30 mM sodium glycerophosphate, pH 6.2.
2. The reactions follow first-order kinetics and the rates are dependent on pH and temperature. The first order rate constants, enthalpies and entropies for the three reactions are sufficiently near each other to suggest that all three reactions are occurring simultaneously.
3. When a muscle is allowed to go into rigor at 37°C the extractability in M KCl–30 mM sodium glycerophosphate is reduced after 4 hr at 37°C when the pH of the muscle has reached 5.55. At the same time the Ca²⁺ adenosine triphosphatase activity falls but the Mg²⁺ adenosine triphosphatase does not. The latter is reduced by prolonging the period at 37°C to 6 hr.
4. It is suggested that there is present in muscle, undergoing rigor at 37°C, myosin which does not bind to actin and is readily denatured. When bound to actin, myosin in the myofibril is more resistant and denatures only after long exposure to a temperature of 37°C.     

THE EFFECTS OF DELAYED PICKING AND HIGH-TEMPERATURE CONDITIONING ON THE TEXTURE OF HOT- AND COLD-BONED BROILER BREAST MEAT

Four trials were conducted to evaluate the effects of delayed picking for 30 min versus normal picking, high temperature conditioning at 32°C versus low temperature conditioning at 0°C, and hot boning versus cold boning on broiler breast meat tenderness, pH, sarcomere length and R-values. None of the treatments affected cold-boned shear values. Within the hot-boned group, delayed picking significantly increased shear value (14.5 kg) compared with normally picked samples (12.5 kg). Conditioning at 32°C significantly lowered shear values (12.5 kg) compared with 0°C (14.6 kg). High-temperature conditioning lowered muscle pH immediately after evisceration, but delayed picking had no effect. Following 24 h aging, treatments had no effect on muscle pH or R-value. These results indicate that 32°C conditioning temperature and early picking significantly reduced meat toughness, but not to a commercially practical degree.     

The effect of high post-mortem temperature on the development of pale, soft and exudative pork: Interaction with ultimate pH

The effects of post-mortem temperature and ultimate pH (pH(u), 24 h post mortem) on the development of the pale, soft and exudative (PSE) characteristics in pig longissimus dorsi muscle were studied. Ten out of the 13 pigs used received pre-slaughter injections of adrenaline in order to deplete muscle glycogen stores. The two muscles from each pig were held at 12 or 35°C during rigor mortis development. Results from covariance analysis, using pH(u) as covariate, showed that a high temperature (35°C) resulted in a dramatic increase in internal light scattering (FOP) 24 h post mortem and a significant decrease in water- and salt-soluble proteins. Cooking loss, sarcomere length and drip loss did not vary significantly with rigor temperature. Interaction between temperature and pH(u) was estimated by assessing the relationship between pH(u) and the difference between the two rigor temperatures for selected traits. The best predictive model was a segmented quadratic model with a plateau which gave significant results for FOP, drip loss, water- and salt-soluble proteins. The effect of temperature decreased curvilinearly when pH increased until a constant value above which no noticeable difference was recorded (drip loss, water- and salt-soluble proteins) or a constant difference was reached (FOP). The pH values corresponding to the convergence points differed from one trait to another. They ranged from 5·72 to 6·22. These results illustrate the importance of muscle glycogen content at slaughter and subsequent pH(u) with regard to the development of temperature-induced PSE meat.     

Tenderness in relation to the temperature of rigor onset in cold shortened beef

Beef sternomandibularis muscle was cold shortened at 2°C for 24 h and then transferred to 37°C until rigor mortis was complete. In spite of a final shortening of 33%, the mean shear value after cooking was identical with that of unshortened meat which had gone into rigor at 15°C. Meat sent into rigor at 2°C with the same degree of shortening had twice the shear value. Thus raising the temperature to 37°C in the final stages of rigor completely nullifies the toughness seen in cold shortened meat, without affecting the shortening. Small changes in cooking loss run parallel to tenderness. The effects are not due to ageing, and may arise from modification of actin–myosin bonding. It is concluded that conditions during the last stages of rigor onset are more important to tenderness than the rest of the post-mortem history of the muscle.     

Short Thermal Treatment Effect on Carp Myofibril and Sarcoplasmic Reticulum: Possible Mechanisms in Rigor Mortis Acceleration by "Arai" Treatment

Inorganic γ-phosphate liberation from adenosine 5′-triphosphate (ATP) by carp myofibrillar ATPase was measured at 0-60°C to elucidate mechanisms in rigor mortis acceleration of sliced carp muscle during washing at a moderately high temperature. ATP splitting within 20 sec in the presence of 5 mM MgCl₂ plus 0.25 mM CaCl₂ was maximal at 45°C, which agreed well with the commercially adopted condition for preparing carp “arai” muscle. In addition, the maximum Ca²⁺ uptake by sarcoplasmic reticulum was observed at 30°C and decreased at higher temperatures. The acceleration of carp muscle rigor mortis at around 45°C was suggested to be partly due to enhancement of myofibrillar Mg²⁺-ATPase activity by increase of intracellular Ca²⁺ concentration.