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 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.     

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

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

宰前处理对畜禽肉品质影响的研究进展

综述了宰前运输、禁食、静养及致晕方式对畜禽宰后肌肉pH、肉色、持水力及嫩度等肉质特性的影响。宰前处理产生的应激反应会改变畜禽宰前体内糖原含量,改变宰后肉中糖酵解和蛋白质降解程度。宰前处理也可能通过应激激素和宰后肉pH变化来影响肉中内源蛋白酶活性,从而导致肉质差异。其中宰前处理造成的宰后糖酵解改变是影响肉质的主要因素。开展针对不同畜种的宰前处理研究,制定出一套适合我国生产实际的宰前处理操作规范,可以避免宰前处理对肉质造成的消极影响,为优质肉的生产提供保障。      

Metmyoglobin reducing activity and colour stability of ovine longissimus muscle

Characteristics of metmyoglobin reducing activity in ovine longissimus were determined, and its effect on colour and colour stability of muscle was investigated in two experiments. In the first experiment vacuum packed ovine longissimus samples were incubated at 5–35°C during the first 16 h post mortem (n=8 per treatment). Metmyoglobin reducing activity was negatively affected by incubation temperatures above 30°C, but colour and colour stability were little affected at 24 h post mortem and after 2 weeks of vacuum storage at 2°C. In the second experiment the effects of pre-slaughter stress and electrical stimulation on metmyoglobin reducing activity, colour and colour stability of ovine longissimus (n=40) with an ultimate pH below 5.8 were investigated. Neither of the treatments had an effect on metmyoglobin reducing activity or colour parameters. The relatively large variation in metmyoglobin activity and colour parameters allowed correlation analysis. Metmyoglobin reducing activity was not correlated to colour or the colour stability parameters. The results of the present study indicate that metmyoglobin reducing activity is not the primary determinant of colour or colour stability of ovine longissimus muscle.     

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

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

钙激活酶与肌肉嫩化的研究

宰后肌肉嫩度的变化是在多种酶的协同作用下完成的,其中一个重要部分是钙激活酶,主要论述了钙激活酶对肌肉嫩化的作用机理、钙激活酶嫩化模型、氯化钙与肉的嫩化和影响钙激活酶活性的因素等方面的内容。     

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

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

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).     

Low stress pre-slaughter handling: effect of lairage time on the meat quality of pork

The effect of lairage time on meat quality was investigated when crossbred pigs were subjected to low stress pre-slaughter handling, where pigs were treated in mixed groups of 15 from the farm to group CO(2) stunning, and where electric goads were not used at any time. Two experiments were carried out, one in spring (n=270) using very standardised conditions and one producer, and one in summer (n=630) using a representative randomly chosen sample of producers. In the first experiment three lairage times were used, less than 30 min (average 26 min), 90 min (average 83 min) and more than 150 min (average 170 min) and no showering. The pH and temperature were measured in the m. longissimus dorsi at various times post mortem, and colour (L(*), a(*), b(*)), internal reflectance and drip loss the day after slaughter. Sensory evaluation was carried out on 16 randomly chosen samples from the shortest and longest lairage time groups. Drip loss, pH(ultimate) and internal reflectance were also measured in the m. biceps femoris and pH(ultimate) and internal reflectance in the m. semimembranosus. Finally, pH(ultimate) was measured in the m. semispinalis capitis. In the second experiment only two lairage times were used, less than 30 min (average 17 min) and more than 130 min (average 150 min) and with intermittent showering and only a subset of the meat quality measurements were made. Lairage time had no effect on any of the meat quality parameters measured in experiment 1. In experiment 2 the shortest lairage time led to a higher temperature in the m. longissimus dorsi at 2 min post mortem, a higher drip loss in the m. biceps femoris and higher internal reflectance values in both muscles the day after slaughter. The differences were, however, very small and may have been an effect of showering.     

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.     

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.     

Influence of age at slaughter, rearing technique and pre-slaughter treatment on some quality traits of lamb meat

The influences of rearing technique and age on muscle fibre type, and of rearing technique, age and pre-slaughter transport on the meat quality characteristics of sheep were investigated using thirty lambs of a Bulgarian coarse-fleeced breed (Karakatchanska). The animals were reared on pasture or in barns and slaughtered at 22 or 30 weeks of age. Muscle fibre type and meat quality were studied in three muscles of different metabolic type—Longissimus dorsi (LD), Supraspinatus (SS) and Rectus abdominis (RA). Fibre type distribution was influenced by age but not by rearing technique. Pigment content of muscles was higher in older animals. Water binding capacity (WBC) increased—and cooking loss decreased—with age. There was an interaction between muscle and pre-slaughter stress with respect to pH, the latter being increased in SS muscle, as was WBC. Cooking loss was decreased by transport stress in the three muscles and by pre-slaughter stress. However, meat organoleptic characteristics (flavour, tenderness and juiciness, as judged by a taste panel) were not influenced by age, rearing technique or pre-slaughter treatment.     

The effects of breed,sex, intramuscular fat and ultimate pH on pork tenderness

A study was conducted to evaluate the influence of breed and sex of animals on tenderness of pork. For evaluation, carcasses of pure breed barrows and gilts of Large White, Czech pig meat, Landrace and Duroc were used. For laboratory investigations, the samples of musculus longissimus lumborum et thoracis (20 mm thick) were taken from the same place, at the first cruciate vertebra 48 h post mortem. Seven days post mortem, the texture of heat-processed meat was measured objectively by the shear method on Instron equipped with Warner–Bratzler shear device. Meat tenderness and juiciness were also evaluated sensorially. It was observed that the tenderness of cooked meat is influenced by breed (the tenderest meat was from Duroc breed). The sex of animals has significant effect on meat tenderness too. At the same time, the effects of pH 45 minutes (pH₄₅) and 24 hours (pH₂₄) post mortem and intramuscular fat content on meat tenderness were evaluated. Correlations were found between shear force (tenderness) and intramuscular fat content and also between shear force and pH value 45 min post mortem. The shear force decreased with increasing intramuscular fat content and with increasing pH₄₅ value. Sensory evaluation of tenderness confirmed the objectively measured data.     

The effect of exercise stress, adrenaline injection and electrical stimulation on changes in quality attributes and proteins in Semimembranosus muscle of lamb

Exercise pre-slaughter has previously been shown to increase drip loss and tenderness in the longissimus muscle of lambs. The mechanism causing higher water loss in post-mortem muscle of lambs is not well understood. This experiment examines the effects of exercise stress, adrenaline injection and electrical stimulation (ES) on meat tenderness and water holding capacity. Forty crossbred lambs (20±2 kg live weight) were used in this study. Meat quality measurements were carried out on the Semimembranosus muscle (SM). The ultimate pH was higher with exercise stress (pH 5.93) compared to controls (pH 5.55; P<0.01). As expected the glycogen levels 30 min and 24 h post-mortem in the exercise stressed (P<0.01) muscle were lower. Lactate concentration at 30 min post-mortem in the electrical stimulation (ES: P<0.05) treated muscle was higher than all other treatment combinations. Myofibrillar protein denaturation, measured by protein solubility, was higher (P<0.05) and the rate of proteolysis of muscle proteins titin and troponin-T, as observed with western blots, increased with exercise stress. However, there were no treatment effects on Warner-Braztler shear force (WBSF). Exercise stress and an interaction with adrenaline caused increased drip loss (P<0.05) and purge (P<0.01) from the muscle. Muscle drip from the exercise stress treatment group had lower Mg(2+) (P<0.01) and K(+) (P<0.01) than controls. The main findings were that exercise stress pre-slaughter increased water loss and the rate of titin breakdown but had no effect on tenderness measured by WBSF. Together the different rates of proteolysis, protein denaturation and ionic conditions may have caused the reduced capacity of the muscle proteins to hold water, despite their relatively high ultimate pH.     

The colour and colour stability of beef Longissimus dorsi and Semimembranosus muscles after effective electrical stimulation

The influence of effective low voltage electrical stimulation (ES) of beef on the colour and colour stability of longissimus dorsi (LD) and semimembranosus (SM) muscles, during storage and retail display was studied by tristimulus colorimetry and reflectance spectrophotometry. ES had no significant effect on the colour of the LD muscles, but some significant effects on SM muscles of ultimate pH 5·5-5·7. Three hours after slicing into steaks at 5 days post mortem, stimulated SM muscles had a paler/lighter colour than non-stimulated controls. During a retail display of 3 days, all steaks exhibited a loss of colour quality manifested in loss of redness and decreases in both hue and chroma (saturation). These changes were most marked in the stimulated SM muscles, and analysis indicated that they were due almost exclusively to the formation of metmyoglobin (metMb). Ageing the meat, as primals cuts, for 33 days at 0°C led to no significant differences in the perceived colour three hours after slicing. The colour changes observed during the 3-day retail display of steaks occurred more rapidly in both (ES and non-ES) 33 day-aged samples than in the 5 day-aged ones. The result of this was that the colour stability of non-stimulated steaks prepared at 33 days was similar to that of ES steaks prepared fresh (5 day post mortem). In SM muscles of pH 5·8-6·0 the apparent differences in colour of the ES and non-ES samples were not significant. However, meat of pH > 5·8, although darker than meat of lesser pH, had less tendency to form metmyoglobin during retail display.

The present work also confirmed that seemingly small differences in display conditions, especially temperature, have a marked effect on metmyoglobin formation.     

Influence of ultimate pH on bovine meat tenderness during ageing

The aim of this work was to evaluate the influence of ultimate pH and ageing at 2±2°C on the tenderness of beef. The m.longissimus thoracis et lumborum from 23 young bulls excised at 28 h post mortem were grouped into: Normal (pH 5.5 to 5.8) moderate DFD (mod DFD) (5.8p<0.05) lower in the DFD group than in the Normal one and a significant (p<0.001) linear relationship was found between ultimate pH and tenderness as evaluated by both methods. The myofibrillar protein solubility (MPS) at pH 7.0 was significantly higher in the DFD group at all post mortem times whereas for myofibrillar fragmentation index (MFI) higher values (p<0.05) were only found in the DFD group at day 1. In all three groups toughness decreased (p<0.05) from 1 to 6 days, with no further decrease to 13 days. This decrease in toughness was associated with an increase of MFI in all pH groups. Collagen solubility in all three groups was not affected by ageing. No significant (p>0.05) differences in soluble collagen and myofibrillar protein solubility (MPS) at pH 5.5 were found between the pH groups at any time. The tenderness evaluated by both methods was significantly (p<0.05) related to MFI, MPS at pH 7.0, cooking loss and juiciness. Total and soluble collagen, sarcomere length, intramuscular fat and MPS at pH 5.5 were not significantly (p>0.05) related with tenderness.     

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

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

Effects of pre-slaughter administration of antifreeze proteins on frozen meat quality

The effects of pre-slaughter administration of antifreeze glycoproteins to lambs were assessed on lamb meat quality after thawing. Various concentrations of antifreeze glycoproteins (AFGP) from Antarctic Cod were injected intravenously into lambs (35 ± 5 kg liveweight) at various times prior to slaughter. The lambs were electrically stunned, slaughtered, then subjected to high voltage electrical stimulation. The rate of glycolysis was assessed by monitoring the rate of pH fall and the ultimate pH. Longissimus dorsi muscles were removed from the carcasses 24 h post-slaughter. Samples were vacuum packed and stored frozen at -20 °C for 2-16 weeks. Upon thawing, samples were assessed for drip loss and sensory properties (foreign flavour, storage flavour, texture, tenderness, juiciness and overall acceptability). At certain times, frozen samples were examined by scanning electron microscopy after ice sublimation. Injection of AFGP had no effect on the rate of pH decline, and for all treatments the pH of samples was not significantly different. Injection of AFGP 10 min before slaughter had no effect at any of the concentrations of AFGP for any of the factors assessed, suggesting that 10 min was insufficient time for the AFGP to become associated with the muscle tissue. Injection of AFGP at either 1 or 24 h before slaughter reduced drip loss and ice crystal size. Crystals were smallest in the lambs injected to a final concentration of 0.01 μg/kg AFGP, particularly when injected 24 h before slaughter. These results suggest that the addition of AFGP could reduce damage due to frozen storage of meat, if a cost-effective and consumer-acceptable method could be developed to incorporate these proteins into meat prior to freezing.