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

Myofibrillar proteins' intermolecular interaction weakening and degradation: Are they mainly responsible for the tenderization of meat containing l-arginine, l-lysine, or/and NaCl?

This study explored the effects of l-arginine, l-lysine, and NaCl alone and in combination on the tenderness of porcine meat. Arg, Lys, and NaCl alone improved the tenderness, decreased the cooking loss, and increased the myofibrillar fragmentation index (MFI) of porcine meat; Both Arg and Lys cooperated with NaCl to better achieve this effect. Furthermore, Arg/Lys collaborated with NaCl to increase muscle fiber swelling and moisture content of the meat and promoted the extraction of main myofibrillar proteins. FT-IR revealed that Arg, Lys, or NaCl alone or in combination caused changes in protein-water interactions. Western blotting revealed varying degrees of meat protein degradation in all cases, but the results did not well coincide with those of shear force and the MFI. Therefore, the weakening of intermolecular forces between myofibrillar proteins was considered the main reason for meat tenderization under the present study conditions.

Effect of accelerated aging on shelf-stability, product loss, sensory and biochemical characteristics in 2 lower quality beef cuts

The aim of this study was to determine the impact of accelerated aging (AA) on shelf stability, product loss, sensory and biochemical characteristics of 2 lower quality beef cuts. Triceps brachii (TB) and semimembranosus (SM) were collected and fabricated from 10 USDA Choice beef carcasses and assigned to 1 of 6 treatments: 3 d cooler aged (control), 21 d cooler aged, AA 49 °C for 2 h, AA 49 °C for 3 h, AA 54 °C for 2 h, and AA 54 °C for 3 h. The results showed that AA can decrease APC counts on steak surface and in purge and redness, but increase lightness and product loss of the steaks (P < 0.01). Lower shear force was also found for AA steaks compared to those from the control (P < 0.01), with the AA 54 °C treatments being comparable to 21 d cooler aging. However, the trained sensory panel determined AA steaks were less juicy and flavorful than those from the control and 21 d cooler aged samples (P < 0.05). There was no off-flavor detected in AA steaks though lipid oxidation was higher in AA samples than those in the control steaks (P < 0.01). The AA treatments stimulated cathepsin activity (P < 0.05), which may have enhanced the solubilization of stromal proteins and led to a different troponin-T degradation pattern compared to those from the 21 d aged samples (P < 0.01). Although AA is an economical and time-efficient method to increase tenderness of lower-quality beef cuts, further research is needed to determine strategies to mitigate the decrease in juiciness from AA treatments.

Impacts of long-time transportation on whiteleg shrimp (Penaeus vannamei) muscle quality and underlying biochemical mechanisms

BACKGROUND

Shrimp is widely consumed around the world. Since muscle is the primary edible component of shrimp, muscle quality (particularly texture) has a direct impact on the economic value of shrimp products. However, reports on the shrimp muscle quality influenced by transportation are rather limited, and the underlying mechanism remains unknown.

RESULTS

During the simulated transportation, the water pH and total ammonia-nitrogen content and un-ionized ammonia contents were elevated. Furthermore, reductions in shrimp muscle water-holding capacity, hardness, and shear value with intensive myofibrillar protein degradation were detected. Simulated transportation decreased the pH and glycogen content of shrimp muscle while increasing lactic dehydrogenase activity and lactate content, resulting in an elevated level of free calcium ions and increased μ-calpain and general proteolytic activities. Water exchange could improve the water quality and reduce the mortality of shrimp during transportation, as well as decrease muscle textural softening by alleviating these stress responses.

CONCLUSIONS

Maintaining water quality and, in particular, reducing ammonia are critical to improving shrimp survival and muscle quality during live transportation. This study is of great significance for the better maintenance of the textural properties of shrimp meat. © 2023 Society of Chemical Industry.

Effect of temporary freezing on postmortem protein degradation patterns

BACKGROUND

A precise determination of time since death plays a major role in forensic routine. Currently available techniques for estimating the postmortem interval (PMI) are restricted to specific time periods or cannot be applied for individual case-specific reasons. During recent years, it has been repeatedly demonstrated that Western blot analysis of postmortem muscle protein degradation can substantially contribute to overcome these limitations in cases with different background. Enabling to delimit time points at which certain marker proteins undergo distinct degradation events, the method has become a reasonable new tool for PMI delimitation under various forensic scenarios. However, additional research is yet required to improve our understanding of protein decomposition and how it is affected by intrinsic and extrinsic factors. Since there are temperature limits for proteolysis, and investigators are confronted with frozen corpses, investigation of the effects of freezing and thawing on postmortem protein decomposition in the muscle tissue is an important objective to firmly establish the new method. It is also important because freezing is often the only practical means to intermittently preserve tissue samples from both true cases and animal model research.

METHODS

Sets of dismembered pig hind limbs, either freshly detached non-frozen, or thawed after 4 months of freeze-storage (n = 6 each), were left to decompose under controlled conditions at 30 °C for 7 days and 10 days, respectively. Samples of the M. biceps femoris were regularly collected at predefined time points. All samples were processed via SDS-PAGE and Western blotting to identify the degradation patterns of previously characterized muscle proteins.

RESULTS

Western blots show that the proteins degrade predictably over time in precise patterns that are largely unaffected by the freeze-and-thaw process. Investigated proteins showed complete degradation of the native protein band, partly giving rise to degradation products present in distinct time phases of the decomposition process.

CONCLUSION

This study provides substantial new information from a porcine model to assess the degree of bias that freezing and thawing induces on postmortem degradation of skeletal muscle proteins. Results support that a freeze-thaw cycle with prolonged storage in frozen state has no significant impact on the decomposition behavior. This will help to equip the protein degradation-based method for PMI determination with a robust applicability in the normal forensic setting.

Relationship between pre-rigor temperature of pork longissimus muscle, myofibril-bound calpain activity and protein degradation

The effect of pre-rigor temperature incubation on the activity and distribution in sarcoplasmic and myofibrillar fractions of calpains, and meat quality attributes was investigated. Porcine longissimus thoracis muscles were incubated pre-rigor at 14, 22, 30 and 38 °C to 6 h postmortem, followed by another 2 h incubation at 14 °C. Thereafter, muscles were stored at 2 °C for 1 or 4 days. With higher pre-rigor temperature, sarcoplasmic Ca²⁺ concentration, purge loss and myofibril-bound calpain-1 content increased, while shear force declined. Water-holding capacity of isolated myofibrils was lower after pre-rigor incubation at 38 °C. Desmin and troponin T degradation, and myofibril fragmentation was greater upon incubation of isolated myofibrils with added Ca²⁺ in the order 800 μM Ca²⁺ > 40 μM Ca²⁺ > no Ca²⁺, suggesting that calpain-1 and calpain-2 were associated to myofibrils and proteolytically active with sufficient Ca²⁺. Activity of myofibril-bound calpain-1 in muscle incubated pre-rigor at 22 and 30 °C were higher than when incubated at 14 and 38 °C. These results indicate that calpains translocate from the sarcoplasm onto myofibrils with higher pre-rigor temperature to 30 °C and the proteolytic potential of myofibril-associated calpains is thereby increased.

Postmortem calpain changes in longissimus muscle from Lanyu native and Kaohsiung crossbred black pigs

The purpose of this study was to compare postmortem calpain changes in porcine muscle between Lanyu native (n = 10) and Kaohsiung crossbred (50% Meishan and 50% Duroc, n = 10) black pigs. Longissimus dorsi (LM) muscles (4th to 10th ribs) from both sides of carcasses were hot-sectioned in 30 min postmortem, vacuum-packaged, and stored at 5°C. LM samples from the left side of carcasses were sampled at 0 (30 min postmortem), 3, 6, 12, 24, 48, and 72 h of storage. The 24 and 72 h samples of shear force measurement were taken from the LM at the 8th and 10th ribs of the right side of carcasses, respectively. Our results showed that the decreases in calpain-1 activity, desmin content, and shear force were slower (P < 0.05) in Lanyu native black pig than in Kaohsiung crossbred black pig samples. Therefore, postmortem proteolysis and tenderization were more limited in LM from Lanyu native pigs than from Kaohsiung crossbred pigs.

Application of gamma radiation in the beef texture development during accelerated aging

This study aimed to evaluate the effects of gamma radiation (3 kGy) on the quality of post-rigor beef (M. longissimus lumborum) aged for up to 21 days at different temperatures (1, 7, and 15°C). Irradiation reduced the mesophilic and lactic acid bacteria counts, which were higher in the non-irradiated samples aged at 7 and 15°C. The water retention capacity was lower in the irradiated beef, resulting in higher values of exudation and cooking losses. High aging temperatures increased the exudation loss and myofibrillar proteolysis (lower fragmentation index; FI) and reduced the total and insoluble collagen contents and the beef Warner-Bratzler square Shear Force (WBsSF). However, irradiated beef had higher FI and SF than non-irradiated ones, increasing the time required for the beef tenderizing. Gamma irradiation (3 kGy) can be used to ensure the microbiological safety during short storage at high temperatures (up to 15°C) in order to accelerate the process of beef tenderizing.

Differences in carcass chilling rate underlie differences in sensory traits of pork chops from pigs with heavier carcass weights

Pork hot carcass weights (HCW) have been increasing 0.6 kg per year, and if they continue to increase at this rate, are projected to reach an average weight of 118 kg by the year 2050. This projection in weight is a concern for pork packers and processors given the challenges in product quality from heavier carcasses of broiler chickens. However, previous work demonstrated that pork chops from heavier carcasses were more tender than those from lighter carcasses. Therefore, the objective was to determine the effects of pork hot carcass weights, ranging from 90 to 145 kg with an average of 119 kg, on slice shear force and sensory traits of Longissimus dorsi chops when cooked to 63°C or 71°C, and to assess if differences in chilling rate can explain differences in sensory traits. Carcasses were categorized retrospectively into fast, medium, or slow chilling-rates based on their chilling rate during the first 17 h postmortem. Loin chops cut from 95 boneless loins were cooked to either 63°C or 71°C and evaluated for slice shear force and trained sensory panel traits (tenderness, juiciness, and flavor) using two different research laboratories. Slopes of regression lines and coefficients of determination between HCW and sensory traits were calculated using the REG procedure in SAS and considered different from 0 at P ≤ 0.05. As hot carcass weight increased, chops became more tender as evidenced by a decrease in SSF (63°C ß = -0.0412, P = 0.01; 71°C ß = -0.1005, P < 0.001). Further, HCW explained 25% (R 2 = 0.2536) of the variation in chilling rate during the first 5 h of chilling and 32% (R 2 = 0.3205) of the variation in chilling rate from 5 h to 13 h postmortem. Slow and medium-rate chilling carcasses were approximately 12 kg heavier (P < 0.05) than fast chilling carcasses. Slice shear force of chops cooked to 63° and 71°C was reduced in slow and medium chilling compared with fast chilling carcasses. Carcass temperature at 5 h postmortem explained the greatest portion of variation (R 2 = 0.071) in slice shear force of chops cooked to 63°C. These results suggest that carcasses tend to chill slower as weight increases, which resulted in slight improvements in sensory traits of boneless pork chops regardless of final degree of doneness cooking temperature.

Biochemical and Physicochemical Changes in Spaghetti Meat During Refrigerated Storage of Chicken Breast

This study investigated postmortem muscle protein degradation and myowater properties in broiler breasts afflicted with the Spaghetti Meat (SM) myopathy during 7 days of storage. Severe SM and unaffected (NORM) breast fillets were analyzed at days 0, 3, and 7 postmortem for TD-NMR myowater traits, myofibrillar protein profiles, calpain activity, free calcium, and desmin and troponin-T degradation patterns. Only at day 0, muscle histology, fiber size and sarcomere length were assessed on multiple fillet portions. In SM breasts, the intramyofibrillar water population exhibited longer relaxation times (p = 0.0172) and a lower proportion (p = 0.0118) compared to NORM. SM had a greater proportion of extramyofibrillar water (p = 0.0080) possessing a longer relaxation time (p = 0.0001). Overall, the SM myopathy had only a minor impact on the myofibrillar proteins profiles and did not affect either free calcium concentration, calpain activity, or the degradation of desmin and TnT, while storage time strongly affected all the traits measured. At microscopic level, muscle tissue from SM fillets exhibited the typical indicators of myodegeneration mostly in the superficial-cranial portion of the breast, while fiber size and sarcomere length were similar between the two muscle conditions irrespectively from the portion considered. The lack of overall significant interaction effects between muscle condition and storage period suggested that SM and NORM breast meat experience similar proteolytic and physical changes during the postmortem period.

Identification of Potential Peptide Marker(s) for Evaluating Pork Meat Freshness via Mass Spectrometry-Based Peptidomics during Storage under Different Temperatures

This study applied peptidomics to investigate potential biomarkers for evaluating pork-meat freshness. The spoilage time points of pork meat stored at −2, 4, 10, and 25 °C were defined by evaluating meat freshness indicators (color, total viable count, pH, and total volatile basic nitrogen). Peptide MVHMASKE was identified as a potential peptide marker via multivariate analysis. Pearson correlation revealed a negative correlation between intensity of MVHMASKE and total viable count/total volatile basic nitrogen. In addition, the correlation between peptide content and the change in pork-meat freshness was verified using real-life samples, and the content of MVHMASKE showed a significant decline during storage under 4 and 25 °C, correspondingly reflecting the change of pork meat from fresh to spoiled. This study provides favorable evidence to evaluate pork-meat freshness by monitoring the change of peptide MVHMASKE in content based on mass spectrometry-based peptidomics.

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.

Effects of chilling rate on progression of rigor mortis in postmortem lamb meat

This work investigated the effects of chilling rate on the progression of rigor mortis and explored possible mechanisms. Silverside from 18 lamb carcasses was assigned to control group (1.94 °C/h), very fast chilling-I group (VFC-I, 12.19 °C/h) and VFC-II group (15.10 °C/h). The shear force, myofibril fragmentation index (MFI), actomyosin ATPase activity, protein degradation and actomyosin dissociation were determined. There was no increase in the shear force in VFC-II group. The activation of actomyosin ATPase at 2-4 h postmortem in VFC-II group resulted in super-contracted sarcomeres and an increase in MFI. The degradation of μ-calpain, troponin T and desmin in VFC-II group was higher than that in control group from 6 to 24 h postmortem. These results suggested that rigor mortis was influenced which resulted in decreased shear force at a chilling rate of 15.10 °C/h by activating actomyosin ATPase and μ-calpain at early postmortem and promoted actomyosin dissociation.

An investigation on the influence of various biochemical tenderness factors on eight different bovine muscles

This study's objective was to understand the relationships between biochemical tenderness components and subject/objective tenderness of eight muscles from beef carcasses. Longissimus thoracis (LT), pectoralis profundus (PP), supraspinatus (SS), triceps brachii (TB), gluteus medius (GM), rectus abdominus (RA), rectus femoris (RF), and semitendinosus (ST) were collected from 10 USDA upper 2/3 Choice beef carcasses and assigned to a two- or 21-day aging period (n=160). Troponin-T (TNT) degradation, desmin degradation, sarcomere length, collagen content, mature collagen crosslink density, intramuscular lipid content, pH, Warner-Bratzler Shear Force (WBSF) and trained sensory panel analyses were measured. A Pearson correlation analysis was conducted to determine the relationship between each tenderness contributor measured in this study with WBSF or the overall tenderness evaluated by the trained panelist for each of the eight muscles. In addition, multivariate regression models were constructed to confirm this relationship. The results showed that muscle anatomical locations and physiological functions driven by muscle fiber types may explain some of the biochemical/tenderness differences found in this study. The correlation analysis showed that each muscle had a specific tenderness factor(s) that contributed to the overall tenderness. For instance, tenderness for LT, TB, GM, RA, and ST may be influenced more by proteolytic degradation, while the collagen characteristics may primarily influence tenderness for PP. Also, lipid content has a significant influence on GM tenderness. Finally, the multivariate regression model showed that almost all of the biochemical measurements conducted in this study played a minor but important role as an overall tenderness predictor on a whole carcass basis. Increasing the knowledge base on the various tenderness components' level of contribution will allow end-users to develop specific tenderness management strategies to ensure consistent tenderness in beef products.

Sarcoplasmic and myofibril-bound calpains during storage of pork longissimus muscle: New insights on protein degradation

The subcellular distribution of calpain-1 and -2 and the proteolytical activity of myofibril-bound calpains in pork were investigated during 12 days cold storage. The content of sarcoplasmic calpain-1 decreased during storage while myofibril-bound calpain-1 content first increased (P < 0.05) to 17% of that of 12 h-sarcoplasmic calpain-1 on day 6 followed by a gradual decrease with subsequent storage, suggesting that calpain-1 gradually translocated from sarcoplasm to myofibrils during the initial 6 days of postmortem storage. Intact desmin decreased (P < 0.05) after incubation of myofibrils with 0.05 mM Ca²⁺, and this was more pronounced with 5 mM Ca²⁺ (P < 0.05). Ca²⁺ titration curves of day 6 myofibrils showed two distinct proteolytic activities becoming activated in the range 0.03 to 0.06 mM and 0.4 to 0.8 mM Ca²⁺, respectively. The results suggest that both calpain-1 and calpain-2 binds to myofibrils during storage and subsequently degrade structural proteins including desmin.

AMP-activated protein kinase contributes to myofibrillar protein hydrolysis in bovine skeletal muscle through postmortem mitochondrial dysfunction-induced apoptosis

This study aimed to verify the role of AMP-activated protein kinase (AMPK) in mitochondrial dysfunction-induced apoptosis and postmortem bovine muscle tenderization. AMPK phosphorylation levels, mitochondrial dysfunction, mitochondrial apoptotic factors, and myofibrillar protein hydrolysis were assessed in the control group and Compound C (AMPK inhibitor) group over a 168 hr aging period. Compared with the Compound C group, the control group had an extremely significantly increased AMPK activity at 6-120 hr (p < .01) and a 62.3% and 42.1% higher mitochondrial Bax/Bcl-2 ratio at 6 and 12 hr, respectively (p < .05). Moreover, the control group had a significantly or extremely significantly higher mitochondrial dysfunction and cytoplasmic cytochrome c content at 6-72 and 12-72 hr, respectively (p < .05, p < .01); a 23.2%, 26.5%, and 26.1% increased caspase-3 expression levels at 12, 24, and 72 hr, respectively (p < .05); a significantly higher proportion of apoptotic nuclei at 24-168 hr (p < .05); and a 30.8%, 35.8%, 43.9%, and 39.5% increased production of 45-, 38-, 36-, 30-, and 28-kDa proteins at 168 hr, respectively (p < .05). Taken together, these results suggested that activated AMPK promoted mitochondrial apoptosis and bovine muscle tenderization during postmortem aging by increasing the Bax/Bcl-2 ratio on the mitochondrial membrane. PRACTICAL APPLICATIONS: Based on consumer preference, chilled fresh meat is gradually becoming the future trend of the meat industry. Poorly tenderized beef often affects consumers' desire to make secondary purchases and leads to large losses to the meat industry. Therefore, AMP-activated protein kinase, which regulates postmortem mitochondrial apoptosis and bovine muscle tenderization, is a valid research target.

Feeding strategies and ageing time alter calpain system proteins activities and meat quality of Braford steers

Objective

The aim of this study was to evaluate the effect of ageing and feeding strategies on the calpain protease system and meat quality traits in Braford steers.

Methods

Thirty Braford steers were employed; 15 animals were supplemented with corn silage during finishing and 15 were kept only on pasture. Meat quality traits and calpain system protein activity were evaluated in longissimus thoracis et lumborum (LTL) steaks aged for 2, 7, 14, and 21 days.

Results

Aged meat showed higher pH and calcium content, while Warner Bratzler shear force (WBSF) decreased to day 21. No interaction between ageing and diet was seen for quality traits. Steers finished with corn silage showed higher values of water holding capacity, WBSF and free calcium, and lower values of pH and cooking loss. Calpain and calpastatin activities decreased with ageing. Finishing steers on pasture produced higher values of calpains and lower values of calpastatin activities. The higher values of calpain 1 activity were observed in muscles aged 2 days from pasture finished animals, and the lower activity of the inhibitor in the 21 days aged samples of the same group.

Conclusion

These results suggest a diet by ageing interaction in calpains and calpastatin and this interaction impact in Warner Bratzler Shear Force in Braford LTL muscle.

Endogenous Proteolytic Systems and Meat Tenderness: Influence of Post-Mortem Storage and Processing

Meat proteolytic systems play a crucial role in meat tenderisation. Understanding the effects of processing technologies and post-mortem storage conditions on these systems is important due to their crucial role in determining the quality characteristics of meat and meat products. It has recently been proposed that tenderisation occurs due to the synergistic action of numerous endogenous proteolytic systems. There is strong evidence suggesting the importance of μ-calpain during the initial post-mortem aging phase, while m-calpain may have a role during long-term aging. The caspase proteolytic system is also a candidate for cell degradation in the initial stages of conversion of muscle to meat. The role of cathepsins, which are found in the lysosomes, in post-mortem aging is controversial. Lysosomes need to be ruptured, through aging, or other forms of processing to release cathepsins into the cytosol for participation in proteolysis. A combination of optimum storage conditions along with suitable processing may accelerate protease activity within meat, which can potentially lead to improved meat tenderness. Processing technologies such as high pressure, ultrasound, and shockwave processing have been reported to disrupt muscle structure, which can facilitate proteolysis and potentially enhance the aging process. This paper reviews the recent literature on the impacts of processing technologies along with post-mortem storage conditions on the activities of endogenous proteases in meat. The information provided in the review may be helpful in selecting optimum post-mortem meat storage and processing conditions to achieve improved muscle tenderness within shorter aging and cooking times.

Influencing Factors on Postmortem Protein Degradation for PMI Estimation: A Systematic Review

The present review provides an overview of the current research status on the effects of influencing factors on postmortem protein degradation used to estimate the PMI (postmortem interval). Focus was set on characteristics of internal and external influencing factors and the respective susceptibility and/or robustness of protein degradation. A systematic literature search up to December 2020 was conducted on the effect of influencing factors investigated in the context of postmortem protein degradation in the tissues of animals and humans using the scientific databases PubMed and Google Scholar, as well as the reference lists of eligible articles. We identified ten studies investigating a total of seven different influencing factors in degrading tissues/organs (n = 7) of humans and animals using six different methodological approaches. Although comparison of study outcomes was impeded by the high variety of investigated factors, and by high risk of bias appraisals, it was evident that the majority of the influencing factors concerned affected protein degradation, thus being able to modulate the precision of protein degradation-based PMI estimation. The results clearly highlight the need for a thorough screening for corresponding factors to enable the introduction of appropriate correction factors and exclusion criteria. This seems especially relevant for the protein degradation-based study of human PMI to increase the reliability and precision of the method and to facilitate a broader applicability in routine forensic casework.

Tenderness-related index and proteolytic enzyme response to the marination of spent hen breast by a protease extracted from Cordyceps militaris mushroom

Objective

The effects of a crude protease extracted from Cordyceps militaris (CM) mushrooms on the postmortem tenderization mechanism and quality improvement in spent hen breast were investigated.

Methods

Different percentages of the crude protease extracted from CM mushrooms were introduced to spent hen breast via spray marination, and its effects on tenderness-related indexes and proteolytic enzymes were compared to papain.

Results

The results indicated that there was a possible improvement by the protease extracted from CM mushroom through the upregulation of endogenous proteolytic enzymes involved in the calpain system, cathepsin-B, and caspase-3 coupled with its nucleotide-specific impact. However, the effect of the protease extracted from CM mushroom was likely dose-dependent, with significant improvements at a minimum level of 4%. Marination with the protease extracted from CM mushroom at this level led to increased protein solubility and an increased myofibrillar fragmentation index. The sarcoplasmic protein and collagen contents seemed to be less affected by the protease extracted from CM mushroom, indicating that substrate hydrolysis was limited to myofibrillar protein. Furthermore the protease extracted from CM mushroom intensified meat product taste due to increasing the inosinic acid content, a highly effective salt that provides umami taste.

Conclusion

The synergistic results of the proteolytic activity and nucleotide-specific effects following treatments suggest that the exogenous protease derived from CM mushroom has the potential for improving the texture of spent hen breast.

Dry-aging of beef as a tool to improve meat quality. Impact of processing conditions on the technical and organoleptic meat properties

Meat consumers are demanding products of higher and consistent quality, with a distinctive flavor and aroma, able to provide a particular sensorial experience when consuming beef. The impact of all the factors affecting the final eating quality, known as the farm to fork approach, has been extensively studied in the last decades. This includes genetic factors, production system, transport, carcass intervention, aging, packaging and cooking method, among others. Aging is, one of the most important steps in producing high quality tender beef. During this step, flavor is developed and the meat is tenderized. Dry-aging although considered a traditional method, is currently attracting attention from consumers, producers and researchers because of the characteristics of the final products in terms of flavor, aroma and texture. This chapter will describe the series of biochemical changes, which combined with the loss of water, generates a final product that is highly appreciated by niche consumers. This will include the changes that the muscle undergoes to be transformed to meat, the main factors driving the dry-aging process and how the flavor and aroma compounds are generated during this process.

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.

Impact of beef carcass size on chilling rate, pH decline, display color, and tenderness of top round subprimals

Beef carcass weights in the United States have continued to increase over the past 30 yr. As reported by the United States Department of Agriculture, grid-based carcass weight discounts begin when carcasses exceed 408 kg. Despite weight discounts, beef carcass weights continue to increase. At the same time, an increased prevalence of discoloration and color variability in top round subprimals has been observed throughout the industry which may be influenced by the increases in carcass weights. The objectives of this study were to assess the effects of beef carcass size and its relationship to chill time, color, pH, and tenderness of the beef top round. In the current study, eight industry average weight beef carcasses (AW, 341–397 kg) and eight oversized beef carcasses (OW, exceeding 432 kg) were evaluated. Temperatures and pH measurements were observed on both sides of all carcasses for the initial 48 h postharvest at a consistent superficial and deep anatomical location of the respective top rounds. Carcasses were fabricated into subprimals at 48 h and top rounds were aged at 2 °C for an additional 12 d. The superficial location of both AW and OW carcasses cooled at a faster rate (P < 0.01) than the deep locations. The deep location of OW carcasses had a lower pH and a more rapid (P < 0.01) initial pH decline. Quantitative color of steaks from OW carcasses had greater mean L* (lightness; P = 0.01) and initial b* (yellowness; P < 0.01) values. The delayed temperature decline and the accelerated pH decline of the deep location of the top round of OW carcasses occur at different rates than AW carcasses. Delayed rate of cooling leads to irreversible impacts on steak appearance of top round steaks fabricated from OW beef carcasses when compared with AW carcasses.

Expression of calpastatin isoforms in three skeletal muscles of Angus steers and their association with fiber type composition and proteolytic potential

This study aimed to evaluate the expression of calpastatin (CAST) isoforms and their potential associations with fiber type composition (%RA), calpastatin activity (CA) and myofibril fragmentation index (MFI) in three muscles with known differences in tenderness (infraspinatus, triceps brachii and semitendinosus) of Angus steers. Expression of total CAST (CAST-T) and CAST isoforms I, II, III (2-3) and III (2-4) (including or not exon 3) was evaluated by qRT-PCR. CAST expression and CA were significantly higher and MFI was lower in semitendinosus, the muscle with the highest %RA of IIX fibers. Differential expression of isoforms defined the variability in CAST-T among muscles. Semitendinosus had a higher expression of isoforms II and III (2-3), but lower expression of III (2-4) compared to the other two muscles. Relative expression of isoforms II and III that were defined by promoter preference linked to alternative splicing, seem to be the main factors explaining differences in CAST expression and ultimately in MFI among muscles.

Calpain activation and proteolysis in postmortem goose muscles

Meat tenderness is considered as the most important criterion for meat quality by consumers and can be improved by the actions of endogenous proteases, mainly calpains, during postmortem storage at 0-5°C. The purpose of this study, therefore, was to examine the postmortem calpain activation and proteolysis in breast (BM) and leg and thigh (LM) muscles of White Roman goose. BM and LM were taken from goose carcasses (n = 15) at 0 (10-15 min postmortem), 1, 3, and 7 days of storage at 5°C. The decrease in postmortem pH, calpain-1 and -11 activities, and contents of the calpain-1 80 kDa subunit and desmin was more rapid (p < .05) in BM than in LM. Our results show that postmortem proteolysis was more extensive in BM than in LM of White Roman goose, not only because the difference in fiber type composition between two muscles, but because the rate and extent of calpain activation were greater in BM as well. These results may provide useful information to optimize meat processing for different muscles in goose industry.

Protein degradation and structure changes of beef muscle during superchilled storage

This study investigated the effect of superchilled storage (-4 °C) on protein degradation and structural changes of beef steaks from M. longissimus lumborum compared with traditional chilling (2 °C) and frozen storage (-18 °C). Traditional chilling induced significantly greater degradation of troponin T and desmin, and more rapid loss of calpain activity, compared to superchilled or frozen storage treatments. The proteolysis of key myofibrillar proteins resulted in a sharp decline of WBSF values during traditional chilled storage. For frozen beef samples, no major changes were observed with respect to protein degradation or muscle structure during storage. However, superchilled samples exhibited wider gaps between muscle fibers at 12 weeks storage, associated with muscle fiber shrinkage.

Changes in Cathepsin Activity during Low-Temperature Storage and Sous Vide Processing of Beef Brisket

It is believed that two main proteolytic systems are involved in the tenderization of meat: the cathepsins and the calpains. Many researchers consider the calpain system to be the major contributor to meat tenderness during post-mortem storage. However, the role and activity of cathepsins during post-mortem storage or low temperature meat processing is unclear, particularly for the tough meat cuts like brisket. Thus, the study was designed to investigate the effects of cold (refrigerated and frozen) storage and sous vide processing on the activities of cathepsin B, H, and L in beef brisket. There were no significant changes in pH and cathepsin H activity throughout the 18 d of storage at both temperatures. However, an increase in cathepsin B activity was observed during the first 4 d at both storage temperatures, but subsequently the activity remained unchanged. Cathepsins B and L were found to be more heat stable at sous vide temperatures (50°C for 24 h, 55°C for 5 h and at 60°C and 70°C for 1 h) compared to cathepsin H. Cathepsin B+L activity was found to increase after sous vide cooking at 50°C for 1 h but decreased to about 47% relative to the uncooked control after 24 h of cooking. These results suggest that cathepsins B and L may contribute to the improved meat tenderness usually seen in sous vide cooked brisket meat.

Effects of µ-calpain oxidation on Coregonus peled myofibrillar protein degradation in vitro

The aim of this study was to evaluate the effect of µ-calpain oxidation on Coregonus peled myofibrillar protein degradation. In the present study, a hydroxyl radical oxidation system was selected to investigate oxidative modification on µ-calpain activity and its degradation on C. peled myofibrillar protein. When subjected to oxidation, the carbonyl content of µ-calpain significantly increased with the increasing of oxidation levels, and oxidation modification promoted the µ-calpain activity. Incubation of C. peled myofibrillar protein with oxidized µ-calpain resulted in the enhanced degradation of myosin heavy chains, actin, and troponin T, but the degradation of desmin at higher levels of oxidation was slightly inhibited, based on sodium dodecyl sulfate polyacrylamide gel electrophoresis and western blotting. This study suggests that oxidation treatment of µ-calpain could accelerate myofibrillar proteolysis through regulating the enzyme activity during postmortem aging. PRACTICAL APPLICATION: Endogenous proteases, especially µ-calpain, are reported to be involved in fish softening during early postmortem storage, which is critical to muscle quality. The cysteine residues of proteins are particularly sensitive to oxidation. The investigation of the effect of oxidation on µ-calpain (a cysteine protease) activity allows for the monitoring of its role in the postmortem proteolysis of fish myofibrils and the associated softening of fish meat, in an attempt to minimize this softening.

Feeding strategies alter gene expression of the calpain system and meat quality in the longissimus muscle of Braford steers

Objective

The aim of the present study was to determine the effect of supplementing pasture-finished steers with corn silage on the expression level of the calpain system proteins and beef tenderization.

Methods

Thirty Braford steers grazing on summer pasture were used for the study. For 120 days fifteen animals were supplemented with corn silage at 1% of body weight per head per day (Suppl) whereas the remaining 15 steers only received pasture (Contr). Carcass and meat traits were evaluated and compared between groups. Gene expression and activities of proteases (calpain 1 and calpain 2) and inhibitor (calpastatin) were measured using real-time polymerase chain reaction and casein zymography.

Results

Carcass and meat traits were significantly different between feeding systems. Supplemented steers showed higher hot carcass weight (p<0.01), fat content (p = 0.02), and Warner-Bratzler shear force (p = 0.03). Furthermore, the control group showed higher protease:inhibitor ratios, at mRNA (p = 0.01) and protein levels (p<0.10). Warner-Bratzler shear force and mRNA calpains:calpastatin ratio were associated in both feeding systems (p<0.01).

Conclusion

Based on the results obtained in the study, beef tenderness differences among finishing strategies could be modulated through differential expression of the calpain system proteins.

The Effect of µ/m-Calpain on Protein Degradation of Chicken Breast Meat

This study was designed to determine the effects of µ/m-calpain on the degradation of cytoskeletal proteins in pectoralis major. Four chickens were slaughtered and the breasts were removed and stored for 12 hr at 4 °C. Each sample was divided into three groups and respectively immersed in control reagent, calpain inhibitor, and caspase inhibitor at 4 °C. The samples were used to evaluate troponin-T and desmin degradation, calpain activity, and myofibril ultrastructure at 12 hr, day 1, day 3, and day 7. Casein zymography revealed that µ-calpain could not be detected in all samples after 12 hr postmortem. The calpain inhibitor inhibited µ/m-calpain activity and reduced troponin-T and desmin degradation during 7 day postmortem. The caspase inhibitor inhibited µ/m-calpain activity and, troponin-T and desmin degradation before day 3 postmortem. The findings suggest that, µ/m-calpain had an effect on cytoskeletal protein degradation after 12 hr postmortem.

Study on the apoptosis mediated by apoptosis-inducing-factor and influencing factors of bovine muscle during postmortem aging

This study investigated the apoptosis pathway mediated by apoptosis-inducing factors (AIF) and internal factors that influence the release of AIF. The results indicated that the AIF expression was decreased in mitochondria and increased in nucleus (P < 0.05). However, no significant differences were observed in the AIF expression in mitochondria with caspase inhibitor treatment. The optical density of nucleus and mitochondrial swelling was significant increased (P < 0.05). Reactive oxygen species (ROS) fell gradually within the first 6 h and increased in the next 24 h. Calpain I activity was decreased, Ca²⁺ concentration, cathepsin B and D activities was increased (P < 0.05). The results demonstrated that AIF-mediated caspase-dependent pathway was a new mitochondrial apoptosis pathway and that mitochondrial swelling, ROS content, Ca²⁺ concentration, calpain I, cathepsin B and cathepsin D activities are the key influencing factors in apoptosis in postmortem bovine muscle.

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.

Effect of extended aging on calpain-1 and -2 activity in beef longissimus lumborum and semimembranosus muscles

Our objectives were to (Exp. 1) determine the effect of postmortem aging (2, 3, 4, 14, 28, and 42days) on calpain-1 and -2 activity in beef longissimus lumborum (LL) and semimembranosus (SM) steaks and (Exp. 2) determine the effect of postmortem aging for two extended periods (63 and 84days) on calpain-2 activity of beef SM steaks. Calpain-1 was not active in either muscle following 14days of aging. Native calpain-2 activity decreased (P<0.001) with longer aging periods for both the LL and SM in Exp. 1 and for the SM in Exp. 2. Autolyzed calpain-2 activity increased (P<0.001) with longer aging for the LL and SM in Exp. 1 and for the SM in Exp. 2. Our results indicate that both calpain-1 and calpain-2 may contribute to the postmortem improvement of beef tenderness, with calpain-1 being responsible for the tenderness improvement early postmortem and calpain-2 responsible for additional tenderization during extended aging.