Combined effect of epinephrine and exercise on calpain/calpastatin and cathepsin B and L activity in porcine longissimus muscle

Development of temperature control algorithm for supercooling storage of pork loin and its feasibility for improving freshness and extending shelf life

Supercooling storage refers to lowering the product temperature below its freezing point without phase transition and has the potential to extend shelf life. Nevertheless, supercooled objects are in a thermodynamically unstable state, and nucleation can occur spontaneously. To achieve supercooling storage, slow cooling and insulation are essential. Hence, a stepwise algorithm for the supercooling storage of pork loins was designed and validated in this study. Pork loins were stored at 3°C, −18°C, and −3°C (freezing), and supercooled for 16 days. All samples remained in a supercooled state and were unfrozen at the end of storage. Supercooled pork loins were superior in terms of drip loss, cooking loss, and water-holding capacity compared to frozen samples. Additionally, supercooling treatment prevented discoloration, increase of volatile basic nitrogen, and microbial growth. Thus, supercooling of pork loin was achieved using a stepwise program and was effective to maintain meat quality.

Cortisol differentially affects the viability and myogenesis of mono- and co-cultured porcine gluteal muscles satellite cells and fibroblasts

Cortisol is a ubiquitously expressed stress hormone. In this study, we investigated the effects of exogenous cortisol on porcine gluteal muscles primary cultured satellite cells and fibroblasts. Satellite cells and fibroblasts were mono-or co-cultured, and cells in each type of culture were categorized into the control and cortisol-treated (treatment) groups. We selected 28 μmol mL^-1 cortisol for treatment based on their efficacy. Cortisol treatment reduced viability of monocultured satellite cells and fibroblasts. In both monocultured and co-cultured cells, the nucleus in the treatment group was damaged than that control group. Moreover, the total cell cycle duration was shorter in the treatment group than the control group. PAX-7 expression was upregulated in the control group of co-cultured satellite cells and fibroblasts than those remaining groups. Moreover, MyoD expression was downregulated in the cortisol treated group of both mono-and co-cultured satellite cells compared with that in the control group. In co-cultured fibroblasts, MyoD and MyoG expression was upregulated than those remaining groups. The Cyto-C expression was upregulated in the treatment group compared to the control mono-and co-cultured both cells. These results suggest that the selected experimental dose of cortisol reduced cell viability and myogenesis-related gene expression in the monoculture compared to that in the co-culture of satellite cells and fibroblasts.

Ca2+-induced binding of calpain-2 to myofibrils: Preliminary results in pork longissimus thoracis muscle supporting a role on myofibrillar protein degradation

The aim of this study was to investigate the role of Ca²⁺ in the process of calpain-2 becoming associated to myofibrils and the potential of myofibril-bound calpain to degrade myofibrillar proteins. Different Ca²⁺ concentrations were applied to myofibrils mixed with partially purified calpain-2. Ca²⁺ induced binding of calpain to myofibrils in a concentration-dependent manner. The half-maximal Ca²⁺ requirements for binding of calpain-2 to myofibrils and for calpain-2 proteolysis of myofibrils were 0.60 mM and 0.29 mM, respectively. To investigate the proteolytic activity of myofibril-bound calpain, a mixture of myofibrils and calpain-2 was briefly incubated with Ca²⁺. Unbound calpain was removed by washing with a Ca²⁺-free buffer. The myofibril-bound calpain maintained proteolytic activity and degraded desmin when re-activated with Ca²⁺. In conclusion, the results suggest that an increase in Ca²⁺ will activate and induce binding of calpain to myofibrils. Subsequently, calpain is relatively tightly bound and proteolytically active.

Proteolysis in pork loins during superchilling and regular chilling storage

This study aimed to address the proteolytic phenomena taking place in pork loins during prolonged storage at superchilling (SC) temperature. Loins were stored at either chilling (CH) conditions (2-4 °C) for 4 weeks or at SC temperature (around -1 °C) for 12 weeks. Storage at SC temperatures slowed down the rate of proteolysis in pork loins, so that final levels of most indicators for proteolysis, including after 12 weeks of SC storage were similar to those after 4 weeks at CH conditions. Consequently, the texture of SC pork under extended storage was not so different to that of CH pork. However, total amino acid content peaked by the end of SC storage, pointing out to a potential ongoing exopeptidase activity. Overall, proteolysis seemed to be slowed down in pork at SC conditions, with similar levels for most indicators after 12 weeks of SC storage or 4 weeks at CH conditions.

Muscle structure, sarcomere length and influences on meat quality: A review

The basic contractile unit of muscle, the sarcomere, will contract as the muscle goes into rigor post-mortem. Depending on the conditions, such as the rate of pH decline, the cooling rate and the mechanical restraints on the muscles, this longitudinal shortening will result in various post-mortem sarcomere lengths as well as lateral differences in the distances between the myosin and actin filaments. This shortening is underlying the phenomena described as rigor contraction, thaw rigor, cold shortening and heat shortening. The shortening in combination with the molecular architecture of the sarcomere as defined by the myosin filaments and their S-1 and S-2 units, the interaction with the actin filaments, and the boundaries formed by the Z-disks will subsequently influence basic meat quality traits including tenderness and water-holding capacity. Biochemical reactions from proteolysis and glycogen metabolism interrelate with the sarcomere length in a complex manner. The sarcomere length is also influencing the eating quality of cooked meat and the water-holding in meat products.

Implementing meta-analysis from genome-wide association studies for pork quality traits

Pork quality plays an important role in the meat processing industry. Thus, different methodologies have been implemented to elucidate the genetic architecture of traits affecting meat quality. One of the most common and widely used approaches is to perform genome-wide association (GWA) studies. However, a limitation of many GWA in animal breeding is the limited power due to small sample sizes in animal populations. One alternative is to implement a meta-analysis of GWA (MA-GWA) combining results from independent association studies. The objective of this study was to identify significant genomic regions associated with meat quality traits by performing MA-GWA for 8 different traits in 3 independent pig populations. Results from MA-GWA were used to search for genes possibly associated with the set of evaluated traits. Data from 3 pig data sets (U.S. Meat Animal Research Center, commercial, and Michigan State University Pig Resource Population) were used. A MA was implemented by combining -scores derived for each SNP in every population and then weighting them using the inverse of estimated variance of SNP effects. A search for annotated genes retrieved genes previously reported as candidates for shear force (calpain-1 catalytic subunit [] and calpastatin []), as well as for ultimate pH, purge loss, and cook loss (protein kinase, AMP-activated, γ 3 noncatalytic subunit []). In addition, novel candidate genes were identified for intramuscular fat and cook loss (acyl-CoA synthetase family member 3 mitochondrial []) and for the objective measure of muscle redness, CIE a* (glycogen synthase 1, muscle [] and ferritin, light polypeptide []). Thus, implementation of MA-GWA allowed integration of results for economically relevant traits and identified novel genes to be tested as candidates for meat quality traits in pig populations.

Long-term changes in performance and meat quality of Danish Landrace pigs: a study on a current compared with an unimproved genotype

An experiment was conducted in 1995 in order to examine muscle growth, muscle histochemical properties, muscle metabolism and meat quality of two types of Danish Landrace pigs representing the growth potential of years 1976 and 1995, respectively. Danish Landrace pigs representing 1976 (slow-growing, SG) originated from a breeding station where the population was maintained without being selected for production traits such as daily gain, food conversion ratio and meat content. Pigs representing Danish Landrace of 1995 (fast-growing, FG) were bought from certified Danish pig breeders. The pigs were simultaneously tested for performance from 40 to 95 kg live weight. The daily gain, food conversion ratio and meat content of the carcass were improved proportionately by 0·43, 0·24 and 0·03 in FG pigs compared with SG pigs. In m. longissimus dorsi (LD), the cross-sectional area of muscle fibres was smaller in FG pigs compared with SG pigs indicating increased muscle fibre number. Data further suggest increased satellite cell proliferation in muscles of FG pigs. Serum from FG pigs stimulated the proliferation of C2C12 muscle cells to a greater extent than serum from SG pigs, although the serum level of insulin-like growth factor 1 did not differ between pig types. The effect of serum on protein turn-over of C2C12 myotubes did not depend on pig type. The glycogen concentration in the LD did not differ significantly between pig types, while the activity of citrate synthase, 3-OH-acyl-CoA-dehydrogenase, and lactate dehydrogenase were higher in the LD of SG pigs compared with FG pigs. Pork chop colour of FG pigs was proportionately 0·09 lighter (L⋆) and 0·13 less red (a⋆) than pork chops of SG pigs. The total muscle pigment concentration in the LD, m. biceps femoris and m. vastus intermedius was proportionately reduced by 0·17, 0·19 and 0·11, respectively, in FG pigs compared with SG pigs. In the LD, the concentration of myoglobin was proportionately reduced by 0·17 in FG pigs. The chemical composition of the LD differed between pig types such that the water content was higher and protein content lower in LD from FG pigs compared with SG pigs. The pH of the LD measured 45 min and 24 h post mortem, drip loss and thawing loss were similar for both pig types. Meat tenderness of conditioned pork chops of FG pigs was slightly reduced in accordance with a decreased intensity of the 31 kDa peptide band and increased cooking loss. The present study suggests that increased muscle fibre number and rate of muscle DNA deposition (satellite cell proliferation) have contributed to the increased muscle growth as a result of selection for performance in pigs under Danish conditions. However, the increase in growth performance was accompanied by deterioration in muscle colour and slightly reduced tenderness.

Effect of cortisol on calpains in the C2C12 and 3T3-L1 cells

The present study was carried out to understand the effect of cortisol on calpain system in the C2C12 and 3T3-L1 adipocyte cells under co-culture system. Cells were co-cultured by using transwell inserts with a 0.4 μm porous membrane to separate C2C12 and 3T3-L1 preadipocyte cells. Each cell type was grown independently on the transwell plates. Following cell differentiation, inserts containing 3T3-L1 cells were transferred to C2C12 plates. Ten microgram per milliliter of cortisol was added to the medium. Following treatment for 3 days, the cells in the lower well were harvested for analysis. Calpains such as μ-calpain, m-calpain, and calpastatin were selected for the analysis. RT-PCR results indicated the significant increase in the mRNA expression of μ-calpain, m-calpain, and calpastatin. In addition, the confocal microscopical investigation indicated the cortisol treatment increases calpain expression in the C2C12 and 3T3-L1 cells. Taking all these together, cortisol treatment with co-culture system shows most reliable status of calpains expression in the cells, which is quite distinct from one-dimensional monocultured cells.

Effects of stress hormone cortisol on the mRNA expression of myogenenin, MyoD, Myf5, PAX3 and PAX7

The present investigation was carried out to evaluate the effect of stress hormone cortisol on the myogenic markers in the C2C12 cells co-cultured with 3T3-L1 preadipocytes. Co-culturing was achieved by transwell inserts with a 0.4 μm porous membrane. C2C12 and 3T3-L1 cells were grown independently on the transwell plates. After differentiation, inserts containing 3T3-L1 cells were transferred to C2C12 plates for co-culturing. 10 μg/μl of cortisol was added to the medium. After 72 h of treatment, C2C12 cells which were in the lower well were harvested for analysis. RT-PCR analysis of myogenic markers such as of myogenin, MyoD, Myf5, PAX3 and PAX7 showed a significant reduction in the mRNA expression of these myogenic markers. In addition, cortisol increased calpain activity, which led to accelerated protein degradation, which in turn reduced the myogenic rate. In conclusion, cortisol treatment reduced mRNA expression of myogenic markers in the co-cultured C2C12 cells, which is quite distinct from one dimensional mono-cultured C2C12 cells.

The development of meat tenderness is likely to be compartmentalised by ultimate pH

Bull Musculus longissimus dorsi (n=63) were categorised into high (pH≥6.2), intermediate (pH 5.8-6.19) and low (≤5.79) ultimate pH (pHu) and aged up to 28 days post mortem at -1°C. High pHu samples were acceptably tender at 1 day post mortem and significantly more tender than low pHu meat at all ageing timepoints (p<0.05). Rapid autolysis of μ-calpain in high pHu meat was linked with the more rapid degradation of titin, nebulin and filamin in this pHu group. Desmin degraded faster in low pHu meat and was concurrent with an increase of cathepsin B levels. The results from this study support the hypothesis that beef tenderisation is pHu compartmentalised with tenderness in high and low pHu meat characterised by variable rate of degradation of high and low molecular weight myofibrillar proteins during ageing, which are in turn regulated by μ-calpain and cathepsin B activities.

Effect of fasting on energy metabolism and tenderizing enzymes in chicken breast muscle early postmortem

Pre-slaughter fasting is a very important practice in the meat industry. The present study was designed to investigate the effect of fasting on energy metabolism and tenderizing enzymes in chicken muscle early postmortem. A total of 30 Yellow-feathered chickens were deprived of feed for 0 h, 12 h and 24 h before slaughter (n=10 each group). Breast muscles were removed and cut into 3 parts and stored at 0°C for 0 h, 3 h and 10 h. Samples were used for analyses of zymography, cathepsins, pH, glycogen/ATP/ADP/AMP, hormones and ultrastructure. Fasting caused the accelerated depletion (p<0.05) of glycogen, ATP and ADP before or immediately after slaughter, but no difference existed in ATP at 3 and 10 h (p>0.05). Fasting resulted in greater ultimate pH (p<0.05). Zymography indicated that fasting delayed the activation of μ/m-calpain (p<0.05), however, it accelerated the release of lysosomal enzymes (p<0.05). Fasting for 24 h resulted in greater ultrastructural changes and plasma corticosterone levels than fasting for 12 h and control groups. Therefore, fasting for no more than 12 h is acceptable in practice.

Effect of rate of pH decline on muscle enzyme activities in two pig lines

Muscle enzyme activities were measured in m. transversus abdominis (TA) samples of two pig lines, differing in stress sensitivity and in breeding objectives. Animals of line one were stress sensitive and selected for a high carcass lean content (LEAN), those of line two were homozygous stress resistant and selected for maximum live weight gain (GROWTH). Muscle samples of 16 pigs per line were excised at 1 h and sampled at 3 h post mortem. Boars, gilts and barrows were almost equally represented. Pigs of line GROWTH had a higher fat and lean tissue gain (P<0.01) and a lower carcass lean content (P<0.001) than those of line LEAN. Lower activities of μ-calpain, m-calpain, pyroglutamyl aminopeptidase I, acid lipase and neutral phospholipase were measured in TA muscle samples of line LEAN compared with line GROWTH (P<0.05). Activities of dipeptidyl peptidase IV and acid phospholipase tended to be somewhat lower for line LEAN, whereas activities of calpastatin, cathepsin (B+L) and cathepsin D were not different. Sex-class effects were analogous to line effects. Significant correlation coefficients between activities of several enzymes and pH values 1 h post mortem, both within and across lines, suggest that lower enzyme activities are a consequence of a more pronounced denaturation due to a faster post mortem pH decline.

The effect of temperature on the activity of μ- and m-calpain and calpastatin during post-mortem storage of porcine longissimus muscle

The experiment was conducted to determine the effect of temperature during post-mortem muscle storage on the activity of the calpain system, the myofibril fragmentation and the free calcium concentration. Porcine longissimus muscle were incubated from 2h post-mortem at temperatures of 2, 15, 25 and 30 °C and sampling times were at 2, 6, 24, 48 and 120 h post-mortem. After 120 h at 30 °C the free calcium concentration increased to 530 μM from 440 μM at 2 °C. Incubation at temperatures higher than 2 °C resulted in the appearance of autolyzed m-calpain activity and a decrease of native m-calpain activity. Native m-calpain decreased more slowly than native μ-calpain, and the autolysis process started later. Myofibril fragmentation increased with storage time and incubation temperature, while calpastatin activity decreased. The study showed that high temperature incubation not only rapidly activated μ-calpain but at higher temperatures and later time points also m-calpain.

Electrical stimulation affects metabolic enzyme phosphorylation, protease activation, and meat tenderization in beef

The objective of this study was to investigate the response of sarcoplasmic proteins in bovine LM to low-voltage electrical stimulation (ES; 80 V, 35 s) after dressing and its contribution to meat tenderization at an early postmortem time. Proteome analysis showed that ES resulted in decreased (P < 0.05) phosphorylation of creatine kinase M chain, fructose bisphosphate aldolase C-A, β-enolase, and pyruvate kinase at 3 h postmortem. Zymography indicated an earlier (P < 0.05) activation of μ-calpain in ES muscles. Free lysosomal cathepsin B and L activity increased faster (P < 0.05) in ES muscles up to 24 h. Immunohistochemistry and transmission electron microscopy further indicated that lysosomal enzymes were released at an early postmortem time. Electrical stimulation also induced ultrastructural disruption of sarcomeres. In addition, ES accelerated (P < 0.05) the depletion of ATP, creatine phosphate, and glycogen, as well as a pH decline and the more preferred pH/temperature decline mode. Finally, ES accelerated meat tenderization, resulting in lesser (P < 0.05) shear force values than the control over the testing time. A possible relationship was suggested between a change in the phosphorylation of energy metabolic enzymes and the postmortem tenderization of beef. Our results suggested the possible importance of the activation of μ-calpain, phosphorylation of sarcoplasmic proteins, and release of lysosomal enzymes for ES-induced tenderization of beef muscle.

A mouse model for monitoring calpain activity under physiological and pathological conditions

Calpains are Ca(2+)-dependent cysteine proteases known to be important for the regulation of cell functions and which aberrant activation causes cell death in a number of degenerative disorders. To provide a tool for monitoring the status of calpain activity in vivo under physiological and pathological conditions, we created a mouse model that expresses ubiquitously a fluorescent reporter consisting of eCFP and eYFP separated by a linker cleavable by the ubiquitous calpains. We named this mouse CAFI for calpain activity monitored by FRET imaging. Our validation studies demonstrated that the level of calpain activity correlates with a decrease in FRET (fluorescence resonance energy transfer) between the two fluorescent proteins. Using this model, we observed a small level of activity after denervation and fasting, a high level of activity during muscle regeneration and ischemia, and local activity in damaged myofibers after exercise. Finally, we crossed the CAFI mouse with the alpha-sarcoglycan-deficient model, demonstrating an increase of calpain activity at the steady state. Altogether, our results present evidence that CAFI mice could be a valuable tool in which to follow calpain activity at physiological levels and in disease states.

Effects of available dietary carbohydrate and preslaughter treatment on glycolytic potential, protein degradation, and quality traits of pig muscles

The current study was conducted to determine the interactive effects of a glycogen-reducing diet fed to finishing pigs and length of preslaughter transportion on muscle metabolic traits, proteolysis of intermediate filament and costameric proteins, and meat quality traits. Large White gilts and barrows (n = 48) were selected at 88 kg of BW and individually fed for 21 d a diet (2.6 kg/d) either high (HC) or low (LC) in available carbohydrates. Six gilts and 6 barrows fed the HC and LC diets were subjected to 0 or 3 h of transportation on the day of slaughter. Muscle temperature and pH were measured at 0.5, 1.5, 2.5, 3.5, 4.5, 5.5, and 24 h postmortem in the LM and 24 h postmortem in the dark (STD) and light (STL) portion of the semitendinosus. At 24 h postmortem, glycolytic potential (GP) was determined in the LM, STD, and STL, as well as proteolysis of titin, nebulin, desmin, vinculin, and talin in the LM and STD. The GP was lower (P < 0.05) in muscles from LC-pigs than in muscles from HC-pigs. The LC diet also resulted in lower (P < 0.05) pH, and a darker (P = 0.03), less (P < 0.01) yellow color in the STL. The LC diet decreased (P = 0.04) cooking losses in the STL and STD. The 3-h journey further decreased (P = 0.05) the GP in the STD, regardless of the diet, but transport had no effect (P > or = 0.67) on the GP of the LM and STL. Ultimate pH of the LM was lower (P = 0.02), and both portions of the semitendinosus were darker (P = 0.01) and less yellow (P < 0.01), in pigs transported 3 vs. 0 h. In pigs transported for 3 h, intact vinculin tended to be more (P = 0.08) degraded in the LM, which coincided with lower (P = 0.04) drip losses in the LM of pigs transported for 3 compared with 0 h. Increased (P < 0.01) proteolysis of titin paralleled lower (P = 0.02) shear force values in the STD of pigs transported 3 vs. 0 h. Although the present results demonstrated the potential of a glycogen-reducing diet to alter the GP of different porcine muscles, the effect of these changes on meat quality traits was limited to higher ultimate pH and darker color in the STL. The positive effects of length of transportation on water-holding capacity (LM and STD) and meat color (STD and STL) were only partially related to the resting muscle glycogen concentration because the 3-h transport lowered the GP only in the muscle with the lowest basal glycogen concentration.

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.

Effect of freezing temperature, thawing and cooking rate on water distribution in two pork qualities

The effects of freezing temperature (-20 versus -80°C) in combination with long-term freezer storage (-20°C) on water mobility and distribution in pork of two qualities (normal and high ultimate pH) were explored using low-field NMR T(2) relaxometry. A marked effect of freezing temperature on the characteristics of intra- and extramyofibrillar water (T(2) relaxation times) in the thawed pork was demonstrated, implying that the freezing temperature in combination with prolonged freezer storage affects the distribution and chemical-physical state of water in the thawed meat. Determination of technological properties (thawing and cooking loss) revealed that the observed T(2) variations related to water distribution and water properties, which were found to be consistent with the degree of structural damage assessed by light microscopy, also were reflected in the technological quality of the meat. Low freezing temperature in combination with prolonged freezer storage was associated with increased thawing and cooking loss. In addition, pH in the fresh meat had a pronounced effect on the distribution of myofibrillar water, as a more homogenous pore size distribution was evident in meat with high pH compared with normal pH. A clear effect of cooking rate on the T(2) relaxation characteristics in the cooked pork was also demonstrated, probably reflecting a cooking rate-induced effect on the myofibrillar structures. The effect of cooking rate on water distribution resulted in a significantly lower cooking loss upon a slow cooking rate (0.5°C/min from 25 to 65°C and 0.3°C/min from 65 to 80°C) compared with a fast cooking rate (1°C/min).

A capillary electrophoresis method to study postmortem proteolysis in relation to pork tenderness

Identification of factors that determine meat tenderness is of high priority. The aim of this work was to develop a method that can detect indicators of proteolysis in meat early postmortem. The method was validated on pork samples. A procedure to detect differences of extractable lower molecular weight compounds after a prerigor freeze/thaw cycle of meat was developed using capillary electrophoresis. The procedure was able to separate 39 peaks in the electropherograms. Eight of the peaks were correlated (P < 0.1) to Warner-Bratzler shear forces 1 day postmortem (WB1). A multiple linear regression model explained 69% of the variation in WB1 using the areas of four peaks. Several of the peaks used in modeling WB1 were related to the at-slaughter activity of the calpain system. The results presented show that the developed method is able to detect indicators of proteolysis and tenderness at an early time point after slaughter. The method is a new tool intended for studies regarding the mechanisms of postmortem proteolysis and tenderization.

Dietary-induced changes of muscle growth rate in pigs: effects on in vivo and postmortem muscle proteolysis and meat quality

The effects of various growth rates in pigs induced by four different feeding strategies on the activity of the calpain system and on postmortem (PM) muscle proteolysis and tenderness development were studied. An increased growth rate may be caused by an increased protein turnover, which results in up-regulated levels of proteolytic enzymes in vivo that, in turn, possibly will affect PM tenderness development. It can be hypothesized that increased proteolytic activity pre-slaughter will increase the PM tenderization rate. From postnatal d 28 to d 90 (phase 1) the pigs were divided into two groups, given either ad libitum (A) or restricted (R, 60% of ad libitum) access to feed. The two groups were then divided into two subgroups, given either restricted or ad libitum access to feed from d 91 to slaughter at d 165 (phase 2). Measurements of the activity of mu-calpain, m-calpain, and calpastatin; concentrations of total collagen and the percent of soluble collagen; and RNA, DNA, and elongation factor-2 where made at slaugther. Myofibrillar fragmentation index (MFI) was determined at slaughter and 24 h PM. Warner-Braztler shear force was determined 1 d and 4 d PM. Pigs fed restricted diets in phase 1 and fed ad libitum in phase 2 (RA pigs) had increased growth rates in the last phase compared to pigs fed ad libitum during both phase 1 and phase 2 (AA pigs). The increased growth rate (compensatory growth) was followed by an increased proteolytic potential (mu-calpain:calpastatin ratio), increased MFI values, and higher tenderization rates. There was a positive correlation between the activities of m-calpain and growth rates (r = 0.35, P = 0.03), and between RNA levels and growth rates (r = 0.43, P = 0.006). The proposed hypothesis is largely supported by the results. The activities of both mu- and m-calpain at slaughter were highest in fast-growing pigs. The calpain activity was highest in RA pigs, which in turn also had the fastest growth rates prior tslaughter among the four groups. This implies that the synthesis of these enzymes was up-regulated during the second feeding period to a larger extent in RA pigs. The proteolytic potential and the MFI values indicate that the up-regulated in vivo calpain activity had an effect on PM protein degradation, which also is supported by the higher tenderization rate in RA pigs.

Identification of protein degradation during post-mortem storage of pig meat

Eighteen proteins and peptides that were found to change post-mortem in Longissimus dorsi from pig muscle were identified by the use of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The 18 peptides originate from 9 different proteins including the 3 structural proteins (actin, myosin heavy chain, and troponin T) and the 6 metabolic proteins glycogen phosphorylase, creatine kinase, phosphopyruvate hydratase, myokinase, pyruvate kinase, and dihydrolipoamide succinyltransferase. The molecular weight and estimated sequence length of the identified spots show that these fragments result from proteolytic activity in meat. Identification of the parent proteins and the enhanced post-mortem appearance of the degradation products make these specific peptides good candidates for meat quality markers, and further studies of these specific fragments will lead to a better understanding of the proteolytic activities involved in the post-mortem conversion of muscle to meat.

Effect of preslaughter feed withdrawal period on longissimus tenderness and the expression of calpains in the ovine

The objective was to study the role of calpains in meat tenderness. Lambs were fasted for various periods of time to generate differences in meat tenderness and to determine in tandem the expression of calpain 1, calpain 2, calpain 3, and calpastatin. The assumption has been that increased calpain expression associated with an increase in tenderness indicates a role for calpain in the tenderization process and vice versa. Fasting lambs for 1 day caused a significant improvement in longissimus (LD) tenderness compared to the control. Correlations between the tenderness of the LD and the expression of the calpains and calpastatin were significant for calpains 1 and 3 but not for calpain 2 or calpastatin. Consequently, this study supports a role for calpains 1 and 3, but not for calpain 2, in the tenderization of the LD from fasted lambs during post-mortem aging.

Epinephrine upregulates calpain activity in cultured C2C12 muscle cells

C2C12 cells were grown to confluence at 37 degrees C under a continuous 5% CO(2) stream and myotube formation was stimulated. The cultures were then incubated with or without 2 microg/mL epinephrine for 18 h prior to harvesting and calpain extraction. Epinephrine treatment resulted in a three-fold increase in extractable mu-calpain activity (P < 0.05), a three-fold increase in extractable m-calpain activity (P < 0.05), a 36% increase in calpastatin activity (P < 0.001), and a 16% decrease (P < 0.05) in the total protein content in the C2C12 cell homogenate. These results suggest that calpains may play a role in protein metabolism and that the hormone epinephrine may be directly involved in the regulation of their cellular expression.