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.     

Post-mortem kinetics of meat tenderness and the components of the calpain system in bull skeletal muscle

Eight strip loins (M. longissimus dorsi) from pasture fed Friesian bulls were aged at 15 °C for a range of times from 1 to 120 h. pH declined from 6.29 (SE 0.119) one hour post slaughter to an ultimate pH of 5.48 (SE 0.013). The activities of the components of the calpain system (μ-calpain, m-calpain and calpastatin) were determined after separation on a DEAE-sephacel column. There was a dramatic decline in μ-calpain activity post slaughter with a complete disappearance within 48 h. The rates of decline in m-calpain and calpastatin activity were slower with 30% and 50% remaining 120 h post slaughter, respectively. The rapid decline in μ-calpain activity relative to the calpastatin activity is likely to reduce the degree of tenderisation and ultimate tenderness of the meat.     

Hind-limb protein metabolism and calpain system activity influence post-mortem change in meat quality in lamb

This study is concerned with the rate of protein turnover in the hind limb muscle bed of intact lambs, the activity of calpain proteolytic system in the M. biceps femoris, and subsequent rates of myofibre breakdown and tenderisation in the M. longissimus dorsi. Feed restriction increased protein degradation in hind-limb muscle of lambs (p<0.1), with a concominant decrease in the extractable activity of calpastatin (p<0.01), the endogenous inhibitor of calpain. IGF-1 analog treatment decreased both protein degradation and assayed μ-calpain activity (p<0.05) with no effect on the activity of calpastatin. β-Agonist treatment increased hind-limb protein synthesis (p<0.01), calpastatin activity (p<0.1) and decreased (p<0.01) μ-calpain activity, but did not effect protein degradation. Significant correlations were observed between Myofibril Fragmentation Index (MFI) values during post-mortem storage and initial post-slaughter calpastatin activity at days 3 (r=-0.34, p<0.1), 5 (r=-0.58, p<0.01) and 9 (r=-0.58, p<0.1), and μ-calpain activity at days 5 (r=0.35, p<0.1) and 9 (r=0.41, p<0.05). However, stronger correlations were observed between the ratio of μ-calpain to calpastatin, an estimate of potential μ-calpain proteolytic activity, and the rate of myofibril fragmentation (r=0.75, p<0.001) and tenderisation (r=-0.64, p<0.01) during aging. These results are consistent with the calpain system being the major proteolytic system involved in myofibril fragmentation and hence aging-related tenderisation of meat.     

Changes in calpain and calpastatin activities of osmotically dehydrated bovine muscle during storage after treatment with calcium

Calpain and calpastatin activities were investigated in calcium-treated beef after osmotic dehydration. Dehydrated beef was soaked in 150 mM calcium chloride solution for 3 h, and then stored for 48 h at 3-4 °C. The untreated sample (control) was soaked in deionized water for 3 h instead of calcium chloride solution, after osmotic dehydration. The increase and decrease in the relative activity of crude calpain were observed in the untreated and the calcium-treated meat, respectively, during the storage. When the crude calpains were subjected to DEAE-Sephacel column chromatography, it was found that μ-calpain activity decreased rapidly during the storage in the untreated meat, whereas there was almost no change in the activity of m-calpain during the storage. The decrease of calpastatin activity was moderate compared with the decrease of μ-calpain activity. In the calcium chloride-treated meat, however, no μ-calpain nor calpastatin activities was detectable after 48 h at cold-room temperature, and m-calpain activity after 48 h had decreased to 6.1% of its activity immediately after thawing. It was concluded that 150 mM calcium chloride treatment after osmotic dehydration was sufficient to introduce calcium ions into the meat. In the presence of sufficient calcium, autolysis of calpains and proteolytic degradation of calpastatin, which eventually related to the rate of decrease in calpain and calpastatin activities, clearly seem to be related to a decrease in meat toughness.     

The effect of time and type of electrical stimulation on the calpain system and meat tenderness in beef longissimus dorsi muscle

Effects of type and time of electrical stimulation on the calpain system, sensory and objective meat quality in the M. longissimus thoracis et lumborum from 38 pasture-fed carcasses, were investigated under conventional chilling conditions. High voltage stimulation was applied to whole carcasses at 3 min post-mortem (pm) and to sides at either 40 or 60 min pm, whilst low voltage stimulation was applied to whole carcasses at 3 min pm and to sides at 40 min pm. Unstimulated sides served as controls. The levels of extractable μ-calpain and calpastatin decreased during stimulation by 28-44% and 8-17%, respectively. Shear force and adjusted tenderness score showed that stimulation at 3 min, irrespective of type of stimulation, resulted in significantly tougher meat (P<0.05) which was associated with an rapid rate of pH decline, compared to stimulation at 40 min. Higher calpastatin levels soon after stimulation at 3 min (P < 0.05) and lower μ-calpain level at 24 h pm for high voltage stimulation at 3 min (P<0.05) coincided with the tougher meat. On the other hand, high voltage stimulation at 40 and 60 min resulted in similar tenderness and levels of μ-calpain and calpastatin post-stimulation and 24 h pm. Significantly tougher meat from the control sides, with a higher μ-calpain levels at 24 h pm and similar sarcomere length, compared to those from low voltage stimulation at 40 min (P<0.001), appeared to be linked to the later activation of the calpain system. Results from the current study suggest that early application of stimulation may be associated with a very rapid decline in pH and consequently a reduction in meat quality.     

Contribution of postmortem muscle biochemistry to the delivery of consistent meat quality with particular focus on the calpain system

Tenderness has been repeatedly reported as the most important quality aspect of meat. However, a number of studies have shown that a significant portion of retail meat can be considered tough. As a consequence, a significant consumer segment is willing to pay a premium for guaranteed tender meat. However, apart from measuring the shear force, there is no reliable method to predict tenderness. Most of the branded meat programs therefore attempt to ensure eating quality by controlling some of the factors that affect tenderness. Meat tenderness is determined by the amount and solubility of connective tissue, sarcomere shortening during rigor development, and postmortem proteolysis of myofibrillar and myofibrillar-associated proteins. Given the effect of postmortem proteolysis on the muscle ultrastructure, titin and desmin are likely key substrates that determine meat tenderness. A large number of studies have shown that the calpain proteolytic system plays a central role in postmortem proteolysis and tenderization. In skeletal muscle, the calpain system consists of at least three proteases, μ-calpain, m-calpain and calpain 3, and an inhibitor of μ- and m-calpain, calpastatin. When activated by calcium, the calpains not only degrade subtrates, but also autolyze, leading to loss of activity. m-Calpain does not autolyze in postmortem muscle and is therefore not involved in postmortem tenderization. Results from a number of studies, including a study on calpain 3 knockout mice, have shown that calpain 3 is also not involved in postmortem proteolysis. However, a large number of studies, including a study on μ-calpain knockout mice, have shown that μ-calpain is largely, if not solely, responsible for postmortem tenderization. Research efforts in this area should, therefore, focus on elucidation of regulation of μ-calpain activity in postmortem muscle. Discovering the mechanisms of μ-calpain activity regulation and methods to promote μ-calpain activity should have a dramatic effect on the ability of researchers to develop reliable methods to predict meat tenderness and on the meat industry to produce a consistently tender product.     

Investigation on CAST, CAPN1 and CAPN3 porcine gene polymorphisms and expression in relation to post-mortem calpain activity in muscle and meat quality

This study aimed to detect variability in CAST, CAPN1 and CAPN3 porcine genes and to investigate the effect of CAST and CAPN1 polymorphisms on the activity of native and autolyzed μ-calpain and m-calpain, measured from 1 to 72 h post-mortem in Longissimus dorsi (LD) muscle of 30 pigs. Effects of polymorphisms on meat quality parameter such as pH, color and drip loss were also evaluated. Samples carrying CAST EU137105:g.76,872AA genotype showed higher autolyzed μ-calpain activity 24 and 72 h post-mortem, as well as lower drip loss values. Expression of CAST, CAPN1 and CAPN3 was assessed in LD muscles divergent for shear force. Higher CAST and CAPN3 expression was found in LD with high shear force (P<0.2), confirming a direct role for calpastatin but not for calpain 3 in meat tenderization. In conclusion, CAST gene affected post-mortem activation time of calpain and drip loss.     

Post-mortem calpain-system kinetics in lamb: Effects of clenbuterol and preslaughter exercise

The effect of dietary supplementation with clenbuterol for either 8 days or 55 days in lambs was studied. The 55-day treatment was combined with an immediate preslaughter exercise regime. The effect of these treatments on post-mortem calpain system activities, meat ageing and meat quality was studied. Neither short-nor long-term supplementation had an effect on the rate of pH fall post mortem. Short-term supplementation had no effect on the initial nor the final shear force values but these were higher at intermediate times. In contrast, prolonged supplementation increased shear force values at all times post mortem. Preslaughter exercise, while influencing the rate of pH decrease in both control and supplemented groups, did not affect meat tenderness. After short-term clenbuterol-supplementation, the in-vitro μ-calpain activity was significantly lower in the supplemented group at 6 and 24 hr post mortem, while m-calpain and calpastatin activities were largely unaffected. In contrast, 55-day clenbuterol supplementation resulted in significantly higher levels of calpastatin activity at all times post mortem. These data imply that clenbuterol results in toughened meat due to alterations in the calpain/calpastatin system, the mechanisms of which are dependent upon the duration of supplementation.     

Tenderization of wether lambs meat through pre-rigor infusion of calcium ions

A study involving 36 wether lamb carcasses was conducted in order to evaluate the effects of 0.3 M CaCl(2) injection on final tenderness in muscle Longissimus thoracis et lumborum. Injection of wether lamb carcasses with CaCl(2) accelerated the post mortem tenderization process. Both control and distilled water injected animals had similar Ca(2+)-dependent proteases (μ-calpain and m-calpain) and their inhibitor (calpastatin) activities, whereas these were all significantly decreased in CaCl(2) injected animals. The effect of CaCl(2) injection on tenderness was recorded by measuring shear force values 2 and 6 days post mortem. Tenderness was significantly improved by CaCl(2) injection at both at 2 and 6 days post mortem. It was concluded that activation of μ-calpain and m-calpain was responsible for the observed post mortem proteolysis and tenderization.     

Factors regulating lamb longissimus tenderness are affected by age at slaughter

The objective of this experiment was to determine age-related changes in collagen concentration, sarcomere length, calpain (μ- and m-) and calpastatin activities, postmortem proteolysis and Warner–Bratzler shear force (WBSF) in ovine longissimus thoracis et lumborum. Rambouillet lambs were slaughtered at 2, 4, 6, 8 and 10 months of age and samples of longissimus were collected at 0, 2 and 10 days postmortem. Collagen concentration and sarcomere lengths were determined from the cores used for WBSF measurements and reflected changes in the background toughness. Longissimus collagen concentration did not change (P>0.05) due to lamb age. Sarcomere lengths also showed age-related changes, increasing (P<0.05) from 1.35 μm at 6 months to 1.48 and 1.55 μm at 8 and 10 months, respectively. The extent of calpain mediated proteolysis determines the improvement in meat tenderness with postmortem storage. The most notable change in the calpain proteolytic system was the decline (P<0.05) in calpastatin activity from 4.18 to 1.91 U/g muscle between 2 and 10 months. The activity of μ-calpain showed a 16% increase (P<0.05) from 4 to 6 months, before it dropped again at 8 and 10 months. There was a gradual decline (P<0.05) in m-calpain activity with age, and by 10 months m-calpain activity had reduced to 80% of 2 months levels. The ratio of μ-calpain to calpastatin activities increased (P<0.05) from 2 to 6 months (from 0.31 to 0.56) with no further changes (P>0.05) at 8 or 10 months. There were no age-related changes (P>0.05) in desmin degradation at day 2, however, examination of day 10 samples showed increased (P<0.05) degradation from 2 to 6 months. Thus, the changes observed in the ratio of μ-calpain to calpastatin activities are reflected in the extent of postmortem proteolysis. Meat tenderness was measured using WBSF at 2 and 10 days postmortem. Because little proteolysis had taken place at 2 days postmortem, the decline in day 2 WBSF from 6 to 8 months could be explained by changes in sarcomere length. However, at 10 days postmortem, where WBSF was shown to decrease from 2 to 8 months, the improvement in tenderness could be explained by the amount of postmortem proteolysis. The data presented in this paper show evidence that sarcomere length is the main determinant of background toughness in ovine longissimus, and that postmortem proteolysis, resulting from μ-calpain activity regulated by calpastatin, is the main determinant of ovine longissimus tenderization during aging. Thus, lamb longissimus tenderness after refrigerated storage is determined by postmortem proteolysis and its interaction with sarcomere length.     

宰后牦牛肉成熟过程中钙激活酶与嫩度指标的相关性分析

以10头甘南牦牛为研究对象,对宰后8d成熟期间肌原纤维小片化指数、剪切力、肌纤维直径、μ-钙蛋白酶(μ-calpain)、m-钙蛋白酶(m-calpain)、钙蛋白酶抑素(calpastatin)的活力进行了测定,同时研究了3种酶活力与肌原纤维小片化指数、剪切力、肌纤维直径3个嫩度指标之间的相关性.结果表明:μ-calpain、m-calpain、calpastatin 3种酶与剪切力值及肌纤维直径均呈正相关;3种酶与肌原纤维小片化指数呈负相关,其中μ-calpain与calpastatin呈显著负相关(P＜0.05).因此,钙激活酶活力的变化可能导致了肌原纤维小片化指数的增加,肌原纤维的弱化和肉的嫩化,μ-calpain可能是牦牛肉嫩化的主要贡献者.     

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).     

钙蛋白酶系统与肌肉嫩度的关系

钙蛋白酶系统主要由钙蛋白酶(μ-calpain,m-calpain)及钙蛋白酶抑制蛋白(calpastatin)组成,calpain是存在于细胞质中的依赖于Ca2+的中性蛋白酶,calpastatin是钙蛋白酶的内源抑制蛋白。本文综述了钙蛋白酶系统各种酶的结构、作用、活性调节机能及其与肉质嫩度的关系。     

Identification of calpastatin, μ-calpain and m-calpain in Atlantic salmon (Salmo salar L.) muscle

A soft fish muscle is generally considered as a poor quality trait among consumers and producers. This degradation and softening of post mortem muscle is thought to be partly caused by proteolytic enzymes such as the calpain system. Separation and identification of μ-calpain and m-calpain and their inhibitor – calpastatin, from Atlantic salmon (Salmo salar) muscle were for the first time assessed in this study. A two-step chromatography approach was used, starting with a hydrophobic interaction column and followed by an anion exchange column. Calpastatin was successfully separated from calpain by hydrophobic interaction chromatography, and following the anion exchange chromatography, two forms of calpastatin (I and II) and two forms of calpain (micro (μ) and milli (m)) were revealed. The proteolytic activity of μ-calpain was detectable with column chromatography, but not consistently detected with casein zymography, and m-calpain was detected with both chromatography and casein zymogram. The proteolytic activity of m-calpain per g muscle was 15 times higher than that of μ-calpain. μ-Calpain had a temperature optimum of 15 °C and a maximum calcium requirement at 0.2 mM, while m-calpain had temperature optimum at 25 °C and a maximum calcium requirement of 0.6 mM. The two forms of calpastatin differed in inhibitory activity with calpastatin II having the highest activity. Both calpastatins tolerated heat treatment, as previously seen for mammals, and they kept their activity when stored at −80 °C, but not at −20 °C. The calpain to calpastatin ratio was 1:4.5 as observed for beef muscle. This study provides evidence that two calpain isoforms, likely to be μ- and m-calpain, in addition to two forms of calpastatin exist in Atlantic salmon muscle.     

The effects of different chilling methods on meat quality and calpain activity of pork muscle longissimus dorsi

The objective of this study was to investigate the effects of conventional chilling (0 to 4 °C), rapid chilling (RC, -20 °C for 30 min, followed by 0 to 4 °C), and short-duration chilling (0 to 4 °C for 30 min, followed by 25 °C) on meat quality and calpain activity of pork muscle longissimus dorsi (LD). The muscle quality characteristics pH, color, cooking loss, pressing loss and tenderness, and calpain activities were measured 0-, 3-, 12-, and 24-h postmortem. Results show that the RC resulted in a faster temperature decline of the muscle, and prevented the meat pH and Commission Internationale de l'Eclairage L* value from declining during postmortem aging. RC also reduced meat cooking loss and pressing loss compared with the other two chilling methods. However, the chilling methods did not significantly affect meat shear force. During the first 24-h postmortem, there was not a noticeable change in the activity of m-calpain. But μ-calpain activity decreased regardless of chilling method. In the rapidly chilled carcasses, μ-calpain activity remained the same 3- and 12-h postmortem. However, in the short-duration chilled and conventionally chilled carcasses, the activity was visibly reduced. At 24-h postmortem, no clear zones on the gel were observed in all three treatments. PRACTICAL APPLICATION: Conventional and RC methods are commonly used for pork in commercial practice nowadays. Compared with conventional chilling, the effect of RC on quality parameters of pork varies. In recent years, short-duration chilling (SC) is widely used in many Chinese pig slaughtering facilities. However, few researchers have studied the effect of SD on pork quality. Therefore, the present study investigated the effect of different chilling methods on functionalities or quality of chilled pork meat.     

Effect of meat ultimate pH on rate of titin and nebulin degradation

The processes involved in the tenderisation of meat were studied on muscles with a range of ultimate pH values (5.4–7.0), produced by subcutaneous injection of various doses of adrenaline and exercise. The m. longissimus thoracicum et lumborum (LD) was removed from carcasses stored at 10 °C and held for 1, 3 or 6 days after slaughter, then frozen until tenderness assessment. The tenderness of meat cooked from the frozen state was determined as the force to shear samples of 10 mm × 10 mm cross-section using a MIRINZ tenderometer. The maximum toughness of 15 kgF occurred at an ultimate pH (pH_u) of about 6.0, resulting in a curvilinear relationship between tenderness and pH_u at 1 day post-slaughter. By 6 days post-slaughter, all meat had reached the same low shear value of approximately 3 kgF. SDS-PAGE patterns obtained from samples at 12, 24 and 48 hr post-slaughter showed increasing titin and nebulin degradation over time, with the slowest rate of degradation occurring at pH_u values 6.0–6.3. Titin and nebulin are known to play an important role in the stabilisation of myofibril structure, and it is suggested that the curvilinear relationship results when pH-dependent titin and nebulin degradation occurs.     

Effect of extraction buffer on estimating calpain and calpastatin activity in postmortem ovine muscle

The effect of extraction buffer on extractable calpain and calpastatin activity in postmortem muscles was examined. Muscles were removed from ovine carcasses 24 h after slaughter and extracted with three volumes of two extraction buffers containing 20?(pH 7.5) and 100 (pH 8.3) mM Tris. There was a significant difference in pH of the muscle homogenates, having a pH of 5.84 and 7.58 for 20 and 100 mM Tris base, respectively. Calpastatin, μ-calpain and m-calpain all had significantly reduced activity in extracts made with 20 mM Tris (pH 7.5) buffer compared to 100 mM Tris (pH 8.3) buffer, showing a loss of, respectively, 30, 57 and 37%. These results indicate the impact of choice of buffer on the extractable calpains and calpastatin activity from postmortem muscle. To avoid loss of calpains due to isoelectric precipitation, the pH of the muscle homogenate (after homogenization and prior to the first centrifugation) must be above 6.2.     

Effect of ion fluid injection on beef tenderness in association with calpain activity

Sodium pyrophosphate plus sodium chloride (PPi) was injected into pre-rigor, hot boned biceps femoris (BF) and semimembranosus (SM) muscle from 12 heifer carcasses. The PPi injection caused higher pH values between 10 and 48 h post-mortem than found in the controls for both muscles (P<0.05). PPi injection resulted in faster decreases in the activities of μ-calpain and calpastatin than in the control for both muscles with time post-mortem (P<0.05). There were significant differences between treatments in both the BF and SM (P<0.05). There was evidence that PPi-injection elevated pH, and accelerated activation of calpains, resulting in improved tenderness. The rates of degradation of titin and troponin-T as well as the appearance of 95 and 30 kDa peptides were faster in the PPi-injected muscles than the controls. PPi-injection elevated muscle pH, which was attributed to acceleration of the calpain activation. It is concluded that PPi-injection improved beef tenderness by accelerating activation of calpain.     

Activities of calpastatin, μ-calpain and m-calpain are stable during frozen storage of meat

The stability of μ-calpain, m-calpain and calpastatin activity during frozen storage of pork was studied in two experiments. In experiment 1, pork longissimus muscle was stored at either -20 or -80°C, and the samples were assayed at 2-3 weeks interval for calpain activity and calpastatin activity using a m-calpain stock solution stored at 4°C. No effects on calpain activity at either temperature were observed for up to 123 days of storage. Calpastatin activity was stable the first few weeks of storage, where after it decreased up to 143 days of storage independently of meat storage temperature. At day 143, calpastatin activity was also assayed using a newly purified stock solution of m-calpain giving a calpastatin activity equal to the activity measured day 0 using the original m-calpain stock solution. The m-calpain stock solution was unstable during storage at 4°C and the activity decreased in a linear manner and was highly related to the observed decrease in calpastatin activity during storage. In experiment 2, meat was stored as in experiment 1 and was assayed at 2-3week intervals for calpastatin activity using a m-calpain stock solution stored at either 4 or -80°C. As in experiment 1, the measured activity of calpastatin decreased during storage using m-calpain stock solution stored at 4°C and this decrease was highly correlated to the decrease in the activity of the m-calpain stock solution. The activity of the m-calpain stock solution stored at -80°C was constant during storage period of 153 days and likewise was the calpastatin activity measured using this stock solution. The relation between measured calpastatin activity and storage time of m-calpain stock solution was tested by adding, to a calpastatin assay, up to 10μL of a partly inactivated m-calpain solution. A negative relationship was observed between added inactivated m-calpain and measured calpastatin activity which suggests that the inactive m-calpain molecules mask some of the binding sites on calpastatin and thereby prevent some of the active m-calpain molecules from binding to calpastatin. This would underestimate the measured calpastatin activity. In conclusion, the calpains as well as calpastatin are stable during frozen storage of meat, and the observed decreased in calpastatin activity is due to instability of the m-calpain stock solution used in the calpastatin assay.     

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.