Manipulation of the pre-rigor glycolytic behaviour of bovine M. longissimus dorsi in order to identify causes of inconsistencies in tenderness

The aim of this study was to monitor the effects of the alteration of the pre-rigor environment of the bovine LD muscle using controlled temperature regimes in order to gain an insight into the early post-mortem pH/temperature/time interactions which are important from the point of view of tenderness and to identify possible reasons for inconsistencies in beef tenderness. LD muscles (n=12) were hot-boned within 90min post-slaughter, cut into three pieces which were randomly placed in polyethylene bags and submerged in water baths pre-set at the following temperatures; 0, 5, 10, 15, 20 and 25°C for 8 h post-mortem then stored at 2°C for up to 14-days post-mortem. The rate of pH decline increased with increasing temperature. Muscles incubated at 0 and 5°C were cold shortened however not all of these muscles were tough as indicated by Warner Bratzler shear force values (WBSF). A pH range of 5.9-6.2 at 3 h post-mortem (pH(3)) produced consistently tender beef where cold-shortening was avoided. Cold shortened muscles showed the greatest variation in tenderness at 14 days post-mortem and underwent the greatest amount of tenderisation (ΔWBSF) and proteolysis between days 2 and 14 post-mortem. Proteolysis of cold shortened muscle may induce variation in tenderness in these muscles.     

Effects of thawing temperature on the physicochemical properties of pre-rigor frozen chicken breast and leg muscles

The objective of this study was to evaluate effects of thawing temperature on the biochemical and physicochemical properties of pre-rigor frozen chicken breast and leg muscles. Breast and leg muscles from 24 broiler chickens were excised within 10min postmortem. Pre-rigor muscles were frozen at -20°C and thawed at 0 and 18°C, and pH, R-value, sarcomere length, muscle shortening, thaw and cook loss, shear force and myofibrillar fragmentation index (MFI) compared with those in pre-rigor or 2°C chilled muscles. The ultimate pH of 18°C thawed muscle was lower than that of 0°C thawed and 2°C chilled muscles. As expected, the shortening of sarcomere length and muscle length of thaw rigor muscles were more than those of chilled muscle, but there were no significant differences between chilled muscle and 0°C thawed muscle. Also, there were no significant differences in R-value (Abs 250/Abs 260) and cook loss due to thawing temperature. Samples thawed at 0°C had higher MFI and lower shear value than samples thawed at 18°C. Shear force value and MFI were not significantly different between chilled muscle and 0°C thawed muscle. By thawing at 0°C, thaw shortening was prevented, and tender meat comparable to the chilled meat was obtained.     

Effects of electrical stimulation, chilling temperature and hot-boning on the tenderness of bovine muscles

The objective of this study was to determine the effects of hot-boning, low voltage electrical stimulation (ES) and chilling temperature on the tenderness of bovine M. longissimus dorsi (LD) and M. semimembranosus (SM) muscles. LD (n=32) and SM (n=32) muscles were subjected to different post-mortem treatments; hot-boning (before 90min post-mortem), cold-boning (at 48h post-mortem), low voltage ES and rapid or slow chilling. Hot-boned muscles which were not electrically stimulated (NES) had higher Warner Bratzler shear force (WBSF) values (P<0.001) and shorter sarcomeres (P<0.001) than cold-boned muscles. Hot-boned muscles subjected to ES had lower pH values (P<0.001) post-stimulation and up to 8h post-mortem than NES muscles. At both chilling temperatures WBSF values were lower in ES hot-boned LD and SM muscles at days 2, 7 and 14 post-mortem than NES muscles. Hot-boned muscles subjected to slow chilling had longer sarcomeres (P<0.001) than those subjected to fast chilling. In hot-boned SM muscles, ES resulted in longer sarcomere lengths (P<0.001). However, ES did not have a significant effect on the sarcomere length of LD muscles. As indicated by WBSF values all muscles tenderised during ageing, including muscles which were 'cold shortened'. Proteolysis was not the main reason for differences in WBSF values between ES and NES muscles as judged by qualitative sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). A combination of slow chilling and ES had a positive effect on hot-boned muscles with respect to WBSF values.     

Effect of very fast chilling and aging time on ultra-structure and meat quality characteristics of Chinese Yellow cattle M. Longissimus lumborum

Objectives of the current study were to evaluate meat ultra-structure and tenderness variation at different chilling regimes and aging times. Hot boned longissimus lumborum of 18 Chinese crossbred cattle were divided into 4 portions per side. One portion underwent very fast chilling (VFC, at -21°C to achieve core temperature of 0°C, then transferred to another incubator at 2°C), whereas other treatments were held at 14, 7 and 0°C for 10h postmortem, respectively. At 10h postmortem, all muscles were vacuum aged at 2°C for 21d. Cold shortened muscles had greatest absolute amount of tenderization during aging. VFC caused lowest sarcomere length, with super-contractions, ruptured Z-lines and myofibril cleavage, but improved myofibril fragmentation index (MFI), with no significant negative effect on toughness. Overall, aging improved the meat quality of cold shortened beef. Moreover, it should be prudent in some applications to apply VFC to excised muscles from a food safety perspective, and to improve tenderness compared to cold-shortened muscles.     

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.     

Bovine muscle shortening and protein degradation after electrical stimulation, excision and chilling

Electrical stimulation-dependent improvement in beef tenderness resulted from mechanisms other than avoidance of cold shortening in excised muscle chilled at a normal rate (10°C at 10h post-stimulation). At normal chilling rate, electrical stimulation enhanced degradation of the myofibrillar proteins, alpha actinin and troponin-T, and increased the amount of a 30 000 dalton protein, as assessed by gel electrophoresis, whereas sarcomere lengths were not different from unstimulated muscle. Under slightly accelerated chilling conditions (10°C at 5 h post stimulation), electrical stimulation prevented cold shortening but the meat was more tender than, and had the same sarcomere length as, unstimulated muscle chilled to 10°C in 10 h. Electrical stimulation did not improve the tenderness of beef chilled at a rapid rate (10°C at 2 h post stimulation), nor did it prevent cold shortening when muscles were chilled rapidly.     

Rapid chilling has no detrimental effect on the tenderness of low-voltage electrically stimulated M. longissimus in Chinese bulls

This study investigated the effect of pre-rigor rapid chilling (RC) on the rate of pH and temperature decline, shear force values and ultrastructure of M. longissimus from beef carcasses exposed to electrical stimulation (ES). Chinese bull carcasses were electrically stimulated, and the alternate sides of the carcasses either were chilled conventionally (CC, 0-4°C, air speed 0.5 m/s for 24 h) or they underwent RC (-14±1°C, air speed 3 m/s for 2 h and then cooled under CC conditions until 24 h post-mortem). The results showed that RC increased the rate of temperature decline (P<0.05) and decreased the rate of pH decline (P<0.05). There were no significant differences in the shear force value and sarcomere length of M. longissimus between the two treatments (P>0.05). The results of this study indicate that RC has no detrimental impact on the tenderness of beef carcasses exposed to ES.     

Pressure-induced pH and length changes in muscle

The response to increase in pressure of pre- and post-rigor muscle strips supporting a load has been investigated by measuring length changes with application of pressure up to 150 MPa in a windowed pressure vessel. The response of the pre-rigor strips depended on temperature; at 30°C the strips contracted, then, after some minutes, lengthened, presumably because of a breakdown of myofibrillar integrity. At 0°C the cold-shortened muscle lengthened but if pressure was released the strips shortened again. Loaded post-rigor muscle strips lengthened with application of pressure. It is suggested that the conditions that prevail in pre-rigor muscle are not as favourable for disaggregation of the myofilaments as those in post-rigor muscle. Measuresurement of pH changes in pre-rigor pressure-treated muscle showed these were accelerated at 30°C, but completely inhibited by treatment at 0°C for 3 or 24h.     

Calpains and calpastatin from cold-shortened bovine M. longissimus lumborum

Sections of beef longissimus lumborum from four animals were held after 1 hr post mortem at either 0 ° (cold-shortened) or at 15 °C (controls). After 24 hr, the levels of μ- and m-calpains were the same in both treatments and about 30% and 85% of their initial levels respectively. The level of calpastatin at 24 h was higher in cold-shortened (100%) than in controls (60% of its initial level). During subsequent storage at 4 °C, the activities of calpains and calpastatin decreased similarly in extracts from both cold-shortened and control muscles. The similar levels of μ-calpain during the first 24 hr post mortem but at the lower temperature suggest that there is less activity under cold-shortening conditions. This, combined with the increased calpastatin levels, would produce less proteolysis by the calpain system. Reduced proteolysis is therefore a factor which should be considered in an understanding of the mechanism of cold-shortening toughness.     

Inhibition of the proliferation of myeloma cells by the meat origin strain Enterococcus faecium CH3

Sides of 31 non-stimulated carcasses of young bulls were subjected to the muscle stretching methods Tenderstretch (TS) by pelvic bone suspension or Tendercut (TC) with two skeletal cuts or served as controls by traditional Achilles tendon suspension. The sides were chilled at fast and medium rates, resulting in temperatures of 4-5 and 9°C in the m. longissimus dorsi (LD) at 10 h post mortem. The LDs were examined for sarcomere length, Warner-Bratzler peak shear force and sensory properties after 8 days of ageing at 4°C. At the fast chilling rate, TS and TC increased sarcomere lengths, reduced shear force and improved sensory tenderness of the LDs compared to the controls (P<0.05). At the medium chilling rate, sarcomere lengths increased (P<0.05), but no significant differences were found in shear force or sensory tenderness (P>0.05) of the muscles due to stretching. However, the medium chilling rate was efficient in producing tender LDs without applying muscle stretching methods. TS and TC are feasible alternatives for improving overall tenderness and reducing variation in tenderness of beef LD at cold shortening chilling conditions.     

Sensory and meat quality traits of pork in relation to post-slaughter treatment and RN genotype

The effects on eating quality and meat quality of two different forms of post-slaughter treatment, performed in an abattoir, were studied in carriers and non-carriers of the RN(-) allele. Carcasses were subjected to rapid and slow chilling, and pelvic and Achilles suspension in a factorial experimental design. A temperature of 10?°C was achieved in the centre of M. longissimus dorsi (LD) within 3.5 h in rapidly chilled carcasses and within 8 h in slowly chilled carcasses. In deep M. semimembranosus (SM) a temperature of 10?°C was achieved within 11.5 h in rapidly chilled carcasses and within 14 h in slowly chilled carcasses. LD from slowly chilled RN(-) carriers suspended by the pelvis exhibited the greatest tenderness, while LD from rapidly chilled non-carriers suspended from the Achilles tendon exhibited the lowest tenderness. Pelvic suspension or slow chilling of non-carriers produced the same improvement in tenderness, and when combined the tenderness increased further. However, the tenderness of the RN(-) carriers was already high, and no significant improvement was seen following any of the studied post-slaughter treatments. Pelvic suspension prevented shortening of muscle fibres, as seen by longer sarcomeres in LD from pelvic-suspended sides. However, longer sarcomeres were associated with greater tenderness only in LD from non-carriers of the RN(-) allele. The presence of the RN(-) allele and a slow chilling regime increased the rate of pH decline in LD. Achilles suspension also increased the rate of pH fall in SM, in addition to the RN(-) allele and slow chilling. The overall tenderness of LD was mainly related to the course of pH decline during rigor; lower pH values between 3 and 7 h post-mortem contributing to greater tenderness. The myofibrillar length was predominantly related to RN genotype and was shorter in RN(-) carriers than in non-carriers. The RN(-) allele and slow chilling contributed to higher evaporation losses and RN(-) carriers exhibited increased frequency of PSE meat in the ham muscles. The use of pelvic suspension appears advantageous over slower chilling, since it improved tenderness without any negative influence on drip loss, evaporation or cooking loss.     

The effect of hot-boning and reduced added phosphate on the processing and sensory properties of cured beef prepared from two forequarter muscles

The functionality of pre-rigor beef was investigated in terms of the effects of phosphate reduction and curing of hot-boned meat on the processing and sensory properties of relatively low-value muscles, M. infraspinatus (IS) and M. pectoralis profundus (PP), from the forequarter. Muscles were excised within 90 min post-mortem (HB) or, from chilled carcasses, 24 h post-mortem (CB), and were injected to 115% of green weight with brine containing phosphate and were vacuum tumbled continuously for 2 h. Hot-boning gave lower total yield of cooked meat for both muscles. Hot-boned PP joints had slightly higher (P < 0.05) cook loss than cold-boned. Reduction of added phosphate (from sodium tri-polyphosphate) from 0.3% to 0.15% of cured meat had detrimental effects on colour; joints containing the conventional 0.3% were lighter (P < 0.001) and redder for both muscles. Hot-boning gave PP joints which were rated less tender by sensory panels, corresponding with higher (P < 0.001) hardness TPA values, higher (P < 0.05) Warner–Bratzler shear force (WBSF) values and shorter (P < 0.05) sarcomere lengths. Effects of phosphate level and boning method were less in IS joints. In these, hot-boning gave products that were rated by sensory panel as slightly more tender but there was no effect on TPA or WBSF values. Furthermore, total yields from hot-boned products did not reflect the expected increase in functionality and reducing added phosphate during processing had a detrimental effect in binding and forming of joints.     

Beef longissimus lumborum, biceps femoris, and deep pectoralis Warner-Bratzler shear force is affected differently by endpoint temperature, cooking method, and USDA quality grade

Effects of endpoint temperature, cooking method, and quality grade on Warner-Bratzler shear force (WBSF) of beef longissimus lumborum (LL), biceps femoris (BF), and deep pectoralis (DP) muscles were evaluated. Eighteen of all three subprimals were selected from USDA Select and 18 from USDA Choice (Certified Angus Beef) carcasses for the respective muscles. Muscles were vacuum packaged and held at 1 °C for 14 days, frozen (-29 °C), sawed into 2.54-cm thick steaks, vacuum packaged, and stored frozen until cooking. Thawed steaks were cooked by either a Magikitch'n(?) electric belt-grill (BG) at 93 °C, or a water-bath at 93 °C, to one of nine endpoint temperatures: 40, 45, 50, 55, 60, 65, 70, 75, or 80 °C. Belt-grill cooking was much faster and resulted in distinctly less cooking loss than water-bath cooking. Water-bath cooking resulted in higher (P<0.0001) Instron(?) WBSF (31.92 N) than BG (28.25 N) for LL. The combination of Select quality grade and higher endpoint temperatures resulted in higher (P<0.05) WBSF for LL. Two distinct phases of tenderization/toughening occurred for BF. Between 40 and 60 °C, WBSF decreased from 43.95 to 38.16 N (P<0.01), whereas between 60 and 70 °C, WBSF increased from 38.16 N to 44.44 N (P<0.05). Water-bath cooling resulted in higher (P=0.0001) DP WBSF (71.12 N) than BG (59.25 N). The DP had a distinct (P<0.0001) decline in WBSF between 45 and 65 °C, irrespective of the cooking method, followed by an increase between 65 and 80 °C (P<0.01).     

Effects of transport time and rest period on the quality of electrically stimulated male cattle carcasses

Ground, pre-salted, pre-rigor semimembranosus muscles of beef were subjected to three treatments A=rapid carbon dioxide (CO(2)) chilling, B=slow CO(2) chilling and C=air chilling, and compared to a control D=slow air chilling of muscles, which were subsequently ground and salted post-rigor. Meat of the pre-rigor treatments A, B and C had higher pH values during processing, lower cooking loss, firmer texture and a lighter yellowish external colour of cooked patties than the post-rigor control D (p<0.05). The two CO(2) chilling regimes A and B had no detrimental effects on the functional properties of the pre-rigor meat. Sarcomere lengths did not differ in meat of the four treatments (p>0.05), indicating that early pre-salting protected the meat from cold shortening during rapid temperature decline. A process combination of grinding, followed by immediate pre-salting and CO(2) chilling within 312h post-mortem of non-stimulated beef muscles is likely to yield superior binding properties of cooked patties and similar ground beef products.     

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/dt 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/dt 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/dt, loss of glycogen, mitochondrial swelling but no gross sarcomere changes. The Longissimus dorsi and Sternomandibularis had a moderate ΔpH and an increase in dpH/dt 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/dt 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.     

Influence of pH on the Warner-Bratzler shear properties of mutton

Initial yield and peak shear force values obtained for stretched muscles cooked at 80°C for different times decreased linearly at a similar rate with increasing pH, which is consistent with the prime effect of pH being on the myofibrillar structure. The tenderising effect of pressure-heat treatment on stretched and cold-shortened muscle decreased rapidly with increase in ultimate pH until, at values near 7, the effect disappeared. Increased ultimate pH effectively eliminated the large increase in shear force values, occurring in cold-shortened muscle of normal pH and attributable to heat denaturation of myosin, as cooking temperature was increased above 60°C.     

The influence of biochemical differences on the variation in tenderness of M. longissimus dorsi of Belgian Blue steers managed homogenously pre and post-slaughter

The objective of this experiment was to determine the contribution of some biochemical processes of postmortem muscle to the variation in tenderness of beef from Belgian Blue bull cross Holstein-Friesian steers (n=10). These animals were managed optimally from conception to consumption with the aim of reducing tenderness variation. The M. longissimus dorsi (LD) from the left hand side (LHS) and the right hand side (RHS) were analysed for variation in tenderness using Bartletts test. The quality measurements included pH, temperature, Warner Bratzler shear force, sensory tenderness, chemical composition and sarcomere length. Biochemical measurements included myofibrilar proteolysis, glycolytic potential, adenine/inosine ratio and collagen content. No difference for variances or means were observed between LHS and RHS for chemical, quality or biochemical attributes. Biochemical variation was greater than the variation observed in most of the quality attributes measured. Proteolysis was the main biochemical contributor to the variation in shear force tenderness after 2 and 7 as postmortem, but not sensory tenderness. Glycolysis levels and adenine/inosine ratio explained much of the variation in sensory tenderness, but not WBSF. Collagen content in the LD muscles did not explain variation in shear force or sensory tenderness. This would suggest biochemical variation is one of the main contributors to variation in tenderness of beef managed optimally pre- and post-slaughter.     

Effect of chilling applied to suckling lamb carcasses on hygienic, physicochemical and sensory meat quality

The effect of post mortem temperature treatment on suckling lamb carcass and meat quality was study. Conventional (2°C for 24h), ultra-rapid (-20°C for 3.5h, 2°C until 24h) and slow chillings (12°C for 7h, 2°C until 24h) were compared. Total viable counts (TVC), weight losses, and pH and temperature falls were recorded on carcasses. Meat colour, water holding capacity (WHC), Warner-Bratzler shear force, sarcomere length and sensory analysis were evaluated in M. longissimus. Ultra-rapid treatment reduced TVC and weight losses. The pH decline was faster in slow chilled carcasses than in faster chilled carcasses. No significant differences were found for colour and WHC. Slow treatment carcasses showed significantly lower shear force and higher sarcomere length. In the sensory analysis, tasters also rated the early post mortem slow-treated meat as more tender, less fibrous and chewy. Therefore, delay chilling in suckling lamb carcasses made it possible to obtain meat with better organoleptic characteristics, without affecting weight loss or hygienic quality.     

Effect of exercise and pre-slaughter stress on pork muscle characteristics

The effects of exercise, stress and chill temperature on pork muscle characteristics were studied in a 3 × 2 × 2 factorial experiment in which treatments were assigned to blocks made up of six pigs of the same sex from the same litter. Pigs were fed a corn-soybean meal diet with the two littermate pigs on each treatment fed together. Treatments were (1) a control group receiving no exercise and fed in an 8 m(2) pen; (2) a treatment group fed in an 8 m(2) pen and driven 1·6 km/day for 100 days prior to slaughter; and (3) a treatment group fed in pens with 40 m(2) floor space with feeders placed 5 m from their waterers. When the animals averaged approximately 105 kg in weight, one animal from each pair treated alike was subjected to standardized stress. After slaughter, one side was chilled at 2-3°C and the other at 13-15°C for 24 h. Both sides were then chilled at 2-3°C for an additional 24 h. Exercise did not affect average daily gain (ADG), feed efficiency, yield of total wholesale cuts, muscle pH, protein solubility, fiber diameter and sarcomere length of the Longissimus dorsi (LD) and Quadriceps femoris (QF) muscles or the tenderness of the QF muscle. Exercise decreased backfat thickness and the subjective tenderness of the LD muscle. The effects of stress on the characteristics evaluated were consistent with those that have been previously reported. Chilling temperature and interactions involving chilling temperature did not affect any of the characteristics studied. No exercise × stress interactions were observed. Protein solubility values indicated that pale, soft exudative (PSE) muscle was not a factor in any of the treatments. It was concluded that exercise will produce leaner carcasses but less tender muscle and that exercise will not counteract the effects of pre-slaughter stress.     

Shortening and tenderness of pre-rigor heated beef: Part 2 - Effect of heating rate on muscles of electrically stimulated carcasses

This study was conducted to compare the effects of rapid and slow heating rates on muscles from electrically stimulated beef carcasses. Myofibrillar and cooking shortening and related changes were measured with physiograph recordings on pre-rigor M. triceps brachii strips suspended in paraffin oil during heating. Warner-Bratzler shear values were determined on pre-rigor and post-rigor M. triceps brachii samples heated at approximately the same rates at which muscle strips were heated (2°C/2 min and 2°C/12 min), on pre-rigor M. triceps brachii samples heated at 2°C/6 min, 2°C/9 min and 2°C/12 min and on pre-rigor and post-rigor M. triceps brachii and M. longissimus muscle heated similarly at 2°C/12 min. Rapid heating (2°C/2 min) of pre-rigor muscle produced more severe myofibrillar shortening that was complete at higher muscle temperature than slow heating (2°C/12 min). Slow heating, in contrast to rapid heating, resulted in a cooked product of lower shear value in both the pre-rigor and post-rigor states. The slower the heating rate of the pre-rigor M. triceps brachii, the more tender was the product. Heating at a rate of 2°C/12 min produced acceptable tenderness in both the pre-rigor M. longissimus and M. triceps brachii muscles but even greater tenderness when both muscles were heated in the post-rigor state. The tenderizing action of severe muscle shortening could not be induced in electrically stimulated muscle.