Rigor Development Research Articles

Near-infrared birefringence and transmittance of pork in relation to pH, sarcomere length, cold-shortening, and causes of paleness

Pork neck muscles, longitudinally restrained during rigor development, were compared with contralateral muscles that were excised and cold-shortened. Restraint had no effect on pH or Japanese pork color scores (JPCS), but restrained muscles had longer (2.52 ± 0.63 μm) sarcomere length (SL) than unrestrained muscles (1.83 ± 0.67 μm, P < 0.005). Transmittance ( T) measurements made on 1 mm slices of pork with unpolarized visible light were strongly affected by pH ( R = 1). But by using near-infrared (NIR) light at 800 nm to reduce scattering, birefringence related both to pH and SL was detected. With some orientations of muscle fibers relative to polarized light, T increased as SL increased from 1.2 to 1.5 μm, peaked at length 1.5 μm, then decreased as length increased to 3.5 μm. Thus, birefringence was proportional to the overlap of thick and thin filaments, until alignment was disrupted by severe shortening. Situations were found where T of polarized light was correlated with SL, R = 0.98 ( P < 0.01). These results support the hypothesis that refraction of light passing through myofibrils may be involved in pH-related paleness in meat.

Prerigor and postrigor changes in tenderness of ovine longissimus muscle.

A novel approach was used to measure the tenderness of prerigor ovine longissimus thoracis et lumborum by avoiding the confounding effects of heat-induced shortening resulting from cooking prerigor meat. The objective was to determine the tenderness of the muscle at the time of slaughter and to monitor changes in tenderness during rigor development and postmortem aging. Nine Romanov and 12 Finnsheep rams were slaughtered at 49.3 kg live weight. Samples of longissimus thoracis et lumborum were removed at 0, 3, 6, 9, 12, 24, 72, or 336 h after exsanguination. Five of the eight sample times were represented in each carcass and all carcasses were sampled at 0, 12, and 24 h. Prerigor muscle samples (0, 3, 6, 9, and 12 h) were clamped between two metal plates before excision to prevent shortening. The samples were frozen at -30 degrees C then stored at -5 degrees C for 10 d to allow glycolysis to proceed to completion, and thus ultimate pH and complete rigor mortis were attained. The longissimus thoracis et lumborum was then cut into chops and cooked and shear force was determined. Sarcomere length decreased through 24 h postmortem, then increased slightly through 336 h postmortem. Warner-Bratzler shear force values were 5.1 kg at 0 and 3 h, increased to 8.3 kg from 3 to 9 h, and then declined to 3.1 kg from 24 to 336 h postmortem. These data imply that longissimus thoracis et lumborum at slaughter is intermediate in tenderness, rigor shortening toughens the meat, and proteolysis tenderizes the meat, resulting in more tender meat after 14 d of aging than at slaughter.

Muscle proteinases and meat aging

The purpose of this manuscript is to review and summarize the results of experiments conducted in our laboratory regarding the mechanism of meat tenderization during post mortem storage of carcasses at refrigerated temperatures. Clearly, the conversion of muscle to meat and the subsequent tenderization process are complex phenomena and much remains to be learned. However, current experimental data suggest that proteolysis of key myofibrillar proteins is the principal reason for improvement in meat tenderness during post mortem storage. Speculatively, the weakening and/or degradation of Z-disks and degradation of desmin (and probably degradation of titin) are responsible for the increased fragility of myofibrils during post mortem storage. There is substantial experimental evidence suggesting that the calpain proteolytic system is resposible for post mortem proteolysis that results in meat tenderization. Calpain is the only proteolytic system that has all of the characteristics that are necessary for bringing about post mortem changes that result in meat tenderization. Undoubtedly, other factors (such as rate pH and temperature decline during rigor development, ionic strength and others) influence the process. However, we believe that the rate and extent of post mortem proteolysis best explain the observed variation in tenderness at a constant age. Therefore, research efforts should be direct toward understanding the regulation of the calpain proteolytic system in post mortem muscle.

The influence of high post-mortem temperature and differing ultimate pH on the course of rigor and ageing in pig Longissimus dorsi muscle

This study was performed in order to assess the effect of temperature and differing ultimate pH (pH u, 24 h post mortem) on the development of rigor mortis in pig Longissimus dorsi muscle. The rigor development (isometric tension and shortening) was measured continuously during the first 24 h post mortem, using an apparatus wherein muscle strips were held at constant temperatures of 12 or 35°C. pH u was manipulated by adrenaline injections preslaughter. The rates of pH fall, adenosine triphosphate (ATP) and creatine phosphate (CP) breakdown were markedly increased at 35°C compared to 12°C. For both temperatures, no delay phase was observed with regard to the development of shortening. Rigor resulted in higher maximum isometric tension and shortening and in shorter time needed to reach maximum values at 35°C than at 12°C. The results are discussed in connection with pH, ATP and CP data. The extent of ageing from 2 to 4 days post mortem, estimated through myofibrillar length determinations, was higher for 12°C than for 35°C. pH u affected significantly most of the traits under study, but its effect depended in some cases upon the rigor temperature. At 12°C, the traits related to the kinetics of rigor development were significantly affected by pH u, but this was not the case at 35°C. Maximum isometric tension was significantly related to pH u at 35°C ( r = 0·86, P < 0·001), but such a relationship was not found at 12°C. Myofibrillar lengths were significantly affected by pH u, but in an opposite manner from one temperature to another. A positive relationship was found at 12°C and a negative one at 35°C. These results illustrate the importance of the interaction between the extent of pH fall and temperature with regard to post-mortem changes in pig muscle.

Optimisation of tenderisation, ageing and tenderness

Tenderness is an important part of meat acceptability and is affected by variations in production and processing. The tenderisation process was modelled on the activity of calpain proteinases. The extent of tenderisation is proportional to the level of calpains which accounts for the toughness of meat from β-adrenergic agonists. The rate of tenderisation increases with higher temperature and faster rigor development. These are responsible for the faster tenderisation in chicken, in meats following the use of electrical stimulation and in meats of high ultimate pH. Knowledge of these mechanisms of tenderisation afforded processes for optimisation of tenderness.

Modelling post-mortem tenderisation—V: Inactivation of calpains

The calpain-activity model, which allows computation of the in-situ activities of calpains, was used to predict tenderisation. Tenderisation results from the net proteolysis which is governed by the relative activities and the intramolecular inactivation of calpains. The activity increases non-interactively with increase in pH and increase in temperature. The rate of inactivation depends interactively upon pH and temperature. At high temperature, inactivation is high and almost independent of pH. The rate of inactivation decreases with decrease in temperature, but below about 10°C it increases at low pH. Rapid rigor development produces rapid activation and tenderisation but it may be short-lived, particularly in slowly-chilled meat, producing tough meat. Rapid cooling causes rapid inactivation of calpains and can give rise to very tough meat. Therefore, the calpain-activity model predicts the toughness often observed in PSE meats and rapidly-chilled meats without evoking structural changes dependent upon water-holding capacity or the degree of overlap of actin and myosin. Furthermore, the model demonstrates the known interactions of ageing with these conditions, interactions which cannot be explained by those structural changes alone. Variations in post-mortem activity of calpains therefore provide a single concept accounting for the variations in texture arising from variations in animal production, chilling and ageing and their interactions.

Flesh Quality in Snapper, Pagrcrs auratus, Affected by Capture Stress

ABSTRACTMuscle metabolites in resting, tank acclimated snapper, Pagrus auratus, were monitored for 72 hr postmortem and compared with values from exercised or commercially caught fish. The physiological status of the live animal was quantified by plasma cortisol and blood chemistry. Cortisol levels were lowest in unstressed controls (6.8 ± 2.1 ng mL−1) while exercised laboratory fish had highest levels (67.7 ± 11.2 ng mL−1). Control fish maintained a constant K‐value for 72 hr in chilled storage; all other groups had significant increases. Onset of rigor development and muscle ATP depletion was delayed in unstressed fish and was more rapid in line‐captured than exercised fish. Commercial users minimizing stress would maintain high flesh quality.

Post-Mortem Biochemistry of Pekin Duckling and Broiler Chicken Pectoralis Muscle

Biochemical post-mortem changes between red and white avian muscle were determined using duckling and chicken Pectoralis muscles, respectively. Six live Pekin ducklings and six live broiler chickens, in each of two trials, were obtained from commercial plants and processed at a pilot facility. After evisceration, carcasses were held at 4 C, then Pectoralis muscles were removed .25, 1, 4, and 24 h post-mortem, and sampled for pH, lactate, adenosine triphosphate (ATP) content, and R-value (inosine to adenine ratio). Duckling Pectoralis pH significantly (P < .05) decreased from 6.25 to 5.66 from .25 to 24 h post-mortem, respectively, as compared with that of the chicken, which decreased from 6.41 to 5.62 for the same times. Duckling lactate values, from .25 to 24 h, increased from 15.86 to 28.86 μmol/g, respectively, and chicken lactate values increased from 27.62 to 53.51 μmol/g. The ATP content of the duckling Pectoralis muscle decreased from 1.59 to .14 μmol/g and chicken Pectoralis decreased from 3.42 to .21 μmol/g from .25 to 24 h, respectively. The R-values of duckling and chicken Pectoralis significantly increased from .25 to 24 h (.98 to 1.37 and .80 to 1.51, respectively). Duckling and chicken biochemical measurements were significantly different at all post-mortem sampling times, except for 24-h values of pH (5.66 versus 5.62, respectively) and 24-h contents of ATP (.14 versus .21 μmol/g, respectively). The different post-mortem biochemical measurements between duckling and chicken Pectoralis muscle is evidence that different rates of post-mortem metabolism and rigor development exist between these red and white avian breast muscles.

POSTMORTEM SHORTENING OF LAMB LONGISSIMUS OXIDATIVE AND GLYCOLYTIC FIBERS

ABSTRACT 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.

Rigor Condition, Tumbling and Salt Level Influence on Physical, Chemical and Quality Characteristics of Cured, Boneless Hams

Influence of pre- or post-rigor conditions, short or long-time tumbling and 1.25 or 2.25% salt on the physical and chemical properties, quality and yield of hams were examined. Curing pre-rigor did not inhibit rigor, but long term tumbling slowed rigor development. Cell disruption and salt-soluble proteins extraction were enhanced more by processing pre-rigor than post-rigor. Pre-rigor intermittent tumbling for 18 hr produced a more uniform cured color and a more desirable slice appearance. Cohesiveness was improved by 18 hr intermittent tumbling. Bind strength at 6 hr intermittent tumbling of pre-rigor tissue was equivalent to that of 18 hr intermittent tumbling, suggesting that curing pre-rigor could reduce tumbling time.

An Evaluation of Simple Methods for Following Rigor Development in Fish

ABSTRACTMeasurements obtained with a simple rigorometer (muscle tension measuring device) were found to correlate well with measurements of the relative ATP/IMP content ratio (258/250 nm absorbance ratio of perchloric extracts), muscle pH, and visual measurements of stiffness in whole fish (tilapia, Areochromis aureus) during rigor development. These simple tests yielded measurements which clearly differentiated the effects of ante‐mortem stress on the rate of onset of rigor mortis and associated biochemical changes in the fish muscle.

Effects of pH and ATP Concentrations on the Heat Contracture of Glycerinated Single Fibers of Rabbit Psoas Muscle

ABSTRACTThe occurrence of heat contracture of glycerinated single fiber of rabbit psoas muscle was investigated in relaxing solutions with varying pH values and ATP concentrations. The threshold temperature for inducing heat contracture of single muscle fibers in relaxing solutions decreases with increasing pH values and decreasing ATP concentrations. There seems to be a relationship between heat contracture of muscle fibers and the tremor of skeletal muscle of porcine stress syndrome. Also, there seems to be a relationship between the heat contracture and alkaline rigor development.

Early Post-Mortem Metabolism and Muscle Shortening in the Pectoralis major Muscle of Broiler Chickens

Three experiments were conducted to examine the effects of sodium pentobarbital (SP), iodoacetate (IO), tubocurarine (TC), and surgical denervation (DN) on early rigor development in broiler breast muscle. In Experiment 1, birds were either anesthetized or not with SP before receiving an injection of IO or TC or maintained as noninjected controls. Experiment 2 was identical except that a treatment of denervation of the breast muscle was added. Experiment 3 was conducted to contrast birds at 1 day (DN1) and 3 days (DN3) denervation prior to slaughter to nonoperated controls. Measurements of muscle lactate, ATP, R value (ratio of inosine to adenine nucleotides), pH, sarcomere lengths, and shear were used to evaluate treatment effects.Results for Experiment 1 showed no significant differences among treatment and control groups for ATP and lactate contents, R values, or sarcomere lengths; however, significantly lower pH and higher shear values were observed for control birds. In Experiment 2, no significant differences were observed among the treatment groups for ATP, R values, or sarcomere lengths. However, lactate and shear values were significantly lower, and pH higher, for the DN and SP treated birds. Experiment 3 resulted in lower lactate and higher pH values for the DN3 treatment in comparison with both DN1 and control groups. Results of these studies indicate that the use of SP and DN can be used to alter the early profiles of rigor development.

Effects of Post-Mortem Wing Restraint on the Development of Rigor and Tenderness of Broiler Breast Meat

Treatments of wing restraint (WR) were applied to broiler carcasses immediately after picking in an attempt to increase tension in the pectoralis (p.) major and restrict muscle shortening during rigor development. In the course of the study, the time allowed for aging prior to deboning of the breast meat was decreased from 4 h to 2 h post-mortem, and the effect on tenderness was determined.Results of deboning at 4 h indicated significantly longer sarcomere lengths for the p. major of wing-restrained carcasses, but shear values of the meat were not decreased. A second experiment tested a modification of the WR, combining a 3-h tie with a “release” interval of 1 h. This treatment combination resulted in higher lactate contents at 4 h, longer sarcomeres, and lower shear values than those of earlydeboned muscles without WR. A modified-WR in abbreviated schemes of deboning at 3 h and 2 h, respectively, resulted in a slight acceleration of post-mortem metabolism in p. major muscles of the WR treatment, a significant increase in sarcomere lengths, and a reduction in the meat toughening associated with early post-mortem deboning. In all of the experiments, WR resulted in significantly reduced sarcomere lengths and toughened meat in the p. minor muscle, consistent with the expected effect of treatment on opposing muscle.

Pectoralis Muscle Shortening and Rigor Development at Different Locations Within the Broiler Breast

Two experiments were conducted to evaluate differences in rigor development that occur as a function of location within the broiler breast muscles, pectoralis major (p. major) and pectoralis minor (p. minor). Three locations were evaluated, corresponding to anterior, middle, and posterior samples taken between the cranial and caudal ends of each muscle. Results of the first experiment indicated that the 1.55-μ sarcomere lengths of hot-boned p. major muscle at the anterior location were significantly shorter than those at the posterior location, which were 1.69 μ. Sarcomere lengths of p. minor were shorter than those of p. major in hot-boned muscles, but longer in those aged intact, indicating a significant muscle × treatment interaction. In the second experiment, the anterior location of hot-boned p. major reached the onset phase of rigor in about 1 h, whereas those at the posterior location required between 2 and 4 h postmortem. Between 1 and 8 h postmortem, sarcomere lengths for the anterior location of p. major were also significantly shorter than lengths in the posterior location, but the differences after 24 h were not significant. Samples at all locations of p. minor reached onset of rigor by 15 to 30 min postmortem, with no locational differences throughout the 24 h period of aging. The results of both experiments generally indicated differences between profiles of rigor development of the two muscles and between samples at different locations of the much larger and more complex p. major.

Effect of Wing Restraint on Postmortem Muscle Shortening and the Textural Quality of Broiler Breast Meat

Two experiments were conducted to evaluate the effects of wing restraint during rigor development on the physical properties of broiler breast meat. Four trials were conducted in the first experiment, using a total of 150 birds. Restraining treatments were applied post-mortem and consisted of an elbow (wing) fixing behind the carcass, lateral extension of the wings and attachment to a bar, and secure binding of the wings together behind the carcass. Results for the first two post-mortem restraints did not indicate significantly different shear values of the meat in comparison with that of the control. However, binding the wings securely behind the carcass toughened (P<.05) cooked meat samples from both pectoralis major and pectoralis minor muscles.The second experiment was conducted to evaluate the effect of ante-mortem wing restraint using treatments of lateral extension of the wings and a modified wing tie that appeared to reduce the severity of treatment on the live bird. In 2 trials using 60 birds, the results indicated longer (P<.05) muscle sarcomere lengths for pectoralis major when using the modified wing tie, although tenderness of the cooked meat was not improved. Lateral extension resulted in longer sarcomere lengths for pectoralis minor, consistent with decreased (P<.05) shear values of the cooked meat. These experiments did not indicate that alternative wing position would improve the textural qualities of broiler breast meat.

Endogenous Proteolytic Enzymes in Skeletal Muscle: Their Significance in Muscle Physiology and During Postmortem Aging Events in Carcasses

This chapter explains the endogenous proteolytic enzymes in skeletal muscle and their significance in muscle physiology, and during postmortem aging events in carcasses. In this chapter, the details about different types of enzymes and their nature are explained. The enzymes with the ability of hydrolyzing peptide bonds are called proteases or proteinases. The proteolytic enzymes, which hydrolyze peptide bonds from the N or C terminus, are called exopeptidases. The author briefs about four types of exopeptidases—namely, aminopeptidases, carboxypeptidases, dipeptidases and dipeptidylpeptidases. The chapter also touches upon endopeptidases in skeletal muscles, such as serine proteinases, thiol proteinases, aspartate proteinases and metalloproteinases, and nonmuscle cathepsins in relation to serine proteinases, thiol proteinases, and unclassified proteinase. It further explains about cellular and subcellular distribution of proteinases in muscle, which is classified in two: catheptic and noncatheptic proteinases, and muscle cell and nonmuscle cell proteinases. There is also a detailed description about significance of endogenous proteinases in muscle physiology and various factors influencing proteinase activity in muscles. The author explains in detail about significance of endogenous proteinases in meat technology in relation to postmortem glycolysis and rigor development, postmortem aging technology, changes in meat during aging process, and enzymology of postmortem aging process.

Responses of different types of ox muscle to electrical stimulation

The effects of electrical stimulation on fall in pH upon stimulation (ΔpH), rate of pH fall (dpH/d t at 35°C, cold shortening and muscle ultrastructure were investigated for the Cutaneus trunci (predominantly fast-twitch glycolytic fibres), the Masseter and Diaphragm (predominantly slow-twitch oxidative fibres) and the Sternomandibularis and Longissimus dorsi (bot fast- and slow-twitch fibres) of the ox. The Masseter and Diaphragm showed a small ΔpH and no increase in dpH/d t upon stimulation. Stimulation produced supercontracture but no tearing of the fibres throughout all of the Masseter. Stimulation of the Cutaneus trunci resulted in a significantly increased ΔpH and dpH/d t, loss of glycogen, mitochondrial swelling but no gross sarcomere changes. The Longissimus dorsi and Sternomandibularis had a moderate ΔpH and an increase in dpH/d t intermediate between that of the Masseter and the Cutaneus trunci. The Longissimus dorsi showed supercontracture, but the Sternomandibularis did not. Cold shortening responses at 2°C and 0°C were virtually unaffected by stimulation, being greatest in the Masseter and Diaphragm and least in the Cutaneus trunci. All muscles showed significantly greater shortenings at 0°C than 2°C. Stimulation of the Cutaneus trunci did not affect the tenderness of the cooked meat, but the toughness increased dramatically in cold-shortened Cutaneus muscle, regardless of stimulation. The Cutaneus trunci least requires stimulation as it does not cold shorten appreciably and therefore early rigor would confer no advantage. The Masseter and Diaphragm have a fast dpH/d t and therefore would enter rigor early. Mixed muscles apparently have the combined, least desirable characteristics of the muscle fibre types—i.e. their rate of rigor development is slow and they cold shorten. Electrical stimulation confers a significant advantage by mitigating these mixed-muscle characteristics in carcass muscles.

Postmortem metabolism of short-finned squid muscle (Illex illecebrosus).

Postmortem biochemical changes were examined in the mantle muscle of the short-finned squid (Illex illecebrosus) in relation to the physical events associated with rigor. Unlike mammalian muscle, the major muscle phosphagen is arginine phosphate rather than creatine phosphate. Arginine phosphate levels did not change dramatically during the progress of rigor development. ATP depletion was found to be closely related to glycogen depletion as is often observed in mammalian muscle. The postmortem accumulation of octopine was related to the initial muscle glycogen content at death but a significant lag in its production was observed. The postmortem conversion of glucose to glucose-6-phosphate appeared to be the rate-limiting step in the overall conversion of glycogen to octopine. The intermediates found in the postmortem catabolism of squid muscle ATP were ADP, AMP, IMP Ino and Hx. Unlike most vertebrate fishes, AMP was found to accumulate in squid before conversion to IMP whereas accumulations of IMP and Ino were less than those normally found in vertebrate muscle.

RELATIONSHIP BETWEEN pH FALL AND INITIATION OF ISOTONIC CONTRACTION IN POSTMORTEM BEEF MUSCLE

Beef muscles were sampled at various times post-mortem both on and off carcass, and the pH, sarcomere length, and isotonic contraction profiles under various loads recorded. The results demonstrate that muscle under light load will begin to contract at pH 6.3 but more heavily loaded muscle will not contract until pH 5.8. Rapid pH fall produced an earlier initiation of contraction than slow pH fall, but the pH required for initiation of contraction under equal loads was the same. The results of isometric tension development followed by unrestrained contraction during the course of rigor development are presented. The authors suggest that both carcass cooling rate and rate of pH fall are implicated in prerigor contraction of postmortem beef muscle.