Postmortem proteome degradation profiles of longissimus muscle in Yorkshire and Duroc pigs and their relationship with pork quality traits

Conversion of muscle to meat is regulated by complex interactions of biochemical processes that take place during postmortem storage of the carcass. Enzymatic proteolysis, among other postmortem biochemical phenomena; e.g. glycolysis; changes tough intact muscle tissue into more tender meat. Knowledge on proteome-wide proteolysis of muscle tissue in relation to meat quality is limited and potential breed-specific differences have received little attention. Therefore, we investigated meat quality traits and proteolysis profiles of the longissimus proteome of five Yorkshire and five Duroc pigs at slaughter and after 1, 2, 3, 7, and 10 days of ageing. Drip loss increased with ageing while cooking loss was unchanged in both breeds. Shear force varied between animals and decreased with ageing. Analysis of the proteomes showed four types of temporal expression profiles. Association analysis suggested several potential protein biomarkers for drip loss and shear force in both breeds, but none for cooking loss.     

The postmortem μ‐calpain activity,protein degradation and tenderness of sheep meat from Duolang and Hu breeds

This study aimed to investigate the differences in meat tenderisation between two Chinese native sheep breeds, Duolang and Hu. The tenderness of longissimus thoracis (LT) muscle, μ‐calpain autolysis and proteolysis of myofibrillar protein was measured at 1‐ and 7‐days postmortem storage at 4 °C. At 7‐days postmortem ageing, meat from Duolang sheep was more tender compared to that from Hu sheep. The Warner–Bratzler shear force of Duolang and Hu sheep was reduced by 55.20% and 41.51% at 7 days compared with 1 day, respectively. In Duolang LT, a higher proportion of 80‐kDa μ‐calpain was autolyzed than in the Hu samples at 1‐day postmortem ageing, but they did not differ significantly at 7 days. More titin, desmin and troponin‐T were degraded in Duolang sheep compared to Hu sheep. Additionally, pH values at the different ageing time were not significantly different, indicating that pH may be not a determinant factor contributing to the tenderness difference between the two breeds. Our data suggest the earlier activation of μ‐calpain and a larger extent of proteolysis of key structural proteins may contribute to the higher rate of tenderisation of Duolang compared to Hu sheep during postmortem ageing.     

Post-harvest interventions to reduce/eliminate pathogens in beef

This study was conducted to assess postmortem proteolysis using a proteomics approach, and to determine the relationship of proteolysis to WB-shear force, drip loss, and hunter L¹ value during chiller ageing in pig longissimus muscle. To generate various meat qualities, 20 male landraces were assigned into 2 × 2 factorial (10 pigs fasted for 18 h and 10 pigs fed until the morning of slaughter × 20 sides placed at −3 °C and 20 sides at 6 °C). An interaction between muscle temperature at pH 6.2 (TpH6.2) and ageing for both WB-shear force and drip loss showed that a high TpH6.2 produced meat with a lower shear force, but the advantage was gradually eroded by extended ageing (i.e., 1, 3 and 7 d). On the other hand, the detrimental effect of a high TpH6.2 on drip loss became more apparent as ageing time increased (i.e., 3 and 7 d). Changes in the objective quality traits and semi-quantitative spot density for 27 out of 133 identified proteins coincided during ageing. The proteins included myosin light chain 1, desmin, troponin T, cofilin 2, F-actin capping protein β subunit, ATP synthase, carbonate dehydratase, triosephosphate isomerase, actin and its relevant peptides, peroxiredoxin 2, α-b crystalline and heat shock protein 27 kDa.     

Effects of phospholipid hydroperoxide glutathione peroxidase mRNA expression on meat quality of <Emphasis Type="Italic">M. longissimus dorsi</Emphasis> in pigs

Antioxidant enzymes protect muscle tissues against oxidation from reactive oxygen species and increase the stability of the muscle. Phospholipid hydroperoxide glutathione peroxidase (GPx4) is an important antioxidant enzyme in muscle tissue. So the aim of this study was to identify the effects of mRNA expression level of GPx4 gene on meat quality properties in Longissimus dorsi of three pig breeds. Total 36 pigs (12 pigs for each breed) were used to measure the meat quality properties and to analyze the expression levels of GPx4 gene by quantitative real-time PCR. The results showed that meat quality, GPx4 activity, and GPx4 mRNA levels were affected by pig breeds. There were the lowest expressible moisture, drip loss, and cooking loss in Laiwu Pig among the three breeds, and also there were the highest GPx4 activity and the expression levels of GPx4 gene in Laiwu Pig compared with the other two pig breeds. Analysis of meat samples divergent for water-holding capacity identified highly negative associations between expressions levels of GPx4 gene and expressible moisture, drip loss and cooking loss. These results suggest that the higher mRNA expression level of GPx4 gene up-regulate the water-holding capacity and the activity of GPx4, and the expression of GPx4 gene plays an important role in physiological changes related to the meat quality properties and the mechanisms of the antioxidant ion of meat.     

Apoptosis during postmortem conditioning and its relationship to duck meat quality

The aim of this work was to examine the relationship of skeletal muscle apoptosis and postmortem development of meat quality. Colour, cooking loss, myofibril fragmentation index (MFI) and shear force of duck breast and thigh meat postmortem were measured, and changes of positive nuclei were assessed with Terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphophate nick end-labelling method (TUNEL). Correlation analysis revealed that apoptosis were positively correlated with colour (L^∗, a^∗ and b^∗), cooking loss and MFI (P < 0.05), while it is negatively correlated with shear force (P < 0.05). Our results indicate the growing level of duck skeletal muscle cell apoptosis was associated with the postmortem development of meat quality traits such as meat colour, water holding capacity and tenderness.     

Effect of fiber type on postmortem proteolysis in longissimus muscle of Landrace and Korean native black pigs

The current study was conducted to characterize objective meat quality, fiber type and their relations to postmortem proteolysis in longissimus muscle of Landrace and Korean native black (KNP) pigs. Longissimus muscles from each 10 market-weighted male pigs were removed after conventional slaughtering and chilling procedures, and aged for 1 or 7 days at 4 °C to determine WB-shear force, objective meat color, proportion of myosin heavy chain I (MyHC I), intramuscular fat content and rate of proteolysis by a proteomics approach. KNP had a significantly (p < 0.05) higher content of MyHC I, and that concurred with greatly (p < 0.05) higher intramuscular fat content and Hunter a^* value, and significantly (p < 0.05) lower drip loss than those seen in Landrace. One-dimension SDS-PAGE indicated that GAPDH, troponin I and creatine kinase were prominent proteolytic products during chiller ageing. By applying a gel-based proteome analysis, 26 proteins were identified, which showed different degradation properties during ageing between the breeds. Biopsied sample revealed that myosin regulatory light chain 2, myosin light chain isotype v/sb, fatty acid-binding protein and albumin were expressed at a greatly higher level for KNP, but their relation to fiber type (or genetic background) is unclear. It was particular noticeable that different actin isoforms showed various degradation behavior during ageing time.     

Validation of a Combi Oven Cooking Method for Preparation of Chicken Breast Meat for Quality Assessment

ABSTRACT: Quality assessment results of cooked meat can be significantly affected by sample preparation with different cooking techniques. A combi oven is a relatively new cooking technique in the U.S. market. However, there was a lack of published data about its effect on quality measurements of chicken meat. Broiler breast fillets deboned at 24‐h postmortem were cooked with one of the 3 methods to the core temperature of 80 °C. Cooking methods were evaluated based on cooking operation requirements, sensory profiles, Warner–Bratzler (WB) shear and cooking loss. Our results show that the average cooking time for the combi oven was 17 min compared with 31 min for the commercial oven method and 16 min for the hot water method. The combi oven did not result in a significant difference in the WB shear force values, although the cooking loss of the combi oven samples was significantly lower than the commercial oven and hot water samples. Sensory profiles of the combi oven samples did not significantly differ from those of the commercial oven and hot water samples. These results demonstrate that combi oven cooking did not significantly affect sensory profiles and WB shear force measurements of chicken breast muscle compared to the other 2 cooking methods. The combi oven method appears to be an acceptable alternative for preparing chicken breast fillets in a quality assessment.     

An evaluation of the growth, carcass and meat quality characteristics of Omani goat breeds

Body weight, growth, carcass and meat quality characteristics were evaluated in three breeds of goats (Batina, Dhofari and Jabal Akdhar) in Oman. Fourteen intact male goats from each breed were used. Jabal Akdhar goats had significantly heavier slaughter, empty body, and carcass weights and higher growth rates than Dhofari and Batina goats. Jabal Akdhar goats had significantly heavier internal organs than the other two breeds. Dressing-out percent (based on empty body weight) of goats ranged between 53 and 57%, with the Dhofari goats having the highest value. Longissimus muscle dimensions varied between the three breeds, with Jabal Akdhar having a significantly larger area than Batina with Dhofari in between. Dhofari goats produced significantly shorter and wider carcasses than Batina and Jabal Akhdar goats. Carcass cuts were significantly heavier in Jabal Akdhar than the other two breeds. Four muscles (Mm. longissimus dorsi, biceps femoris, semitendinosus, and semimembranosus) from both sides of each carcass were subjected to two different ageing periods (1 day vs. 6 day) and evaluated for ultimate pH, expressed juice, percent cooking loss, colour (L*, a* and b*), and Warner-Bratzler shear force. Breed had a significant influence on pH and percent cooking loss but not on expressed juice, shear force value and colour (CIE L*,a*, b* values). Muscles from the Batina goats had significantly higher ultimate pH values and lower percent cooking loss than Dhofari and Jabal Akdhar goats. Ageing from 1 to 6 days increased tenderness significantly (27%), but decreased cooking loss by 5%.     

Effect of Pulsed Electric Field Treatment on Cold-Boned Muscles of Different Potential Tenderness

Despite the release of several reports highlighting the potential benefits of pulsed electric field (PEF) technology in food processing, there are limited studies on the use of PEF in meat processing, in particular with fresh meat. The effect of PEF on the quality of beef loins (Musculus longissimus lumborum, LL) at 1 day postmortem and topsides (Musculus semimembranosus: SM) at 1 and 3 days postmortem was investigated using a range of treatment combinations [voltages (5 and 10 kV) and frequencies (20, 50 and 90 Hz)]. The investigated parameters were purge loss, cooking loss and meat tenderness (shear force) to identify the optimum PEF treatment conditions for each muscle to evaluate the economic (in terms of purge and cooking losses) and texture benefits of PEF treatments. The tenderness of the loin samples was found to benefit from PEF treatment (19.5 % reduction in the shear force) regardless of the electrical input, whereas the level of tenderness of the topsides was increased by increasing the treatment frequency (4.1, 10.4 and 19.1 % reduction in the shear force at 20, 50 and 90 Hz, respectively). Higher purge loss (%) and lower cooking loss (%) were found in PEF-treated samples. It is interesting to observe that the level of SM tenderness improvement was not dependent on the meat postmortem time up to 3 days which allows greater flexibility in the use of PEF technology.     

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

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

Electrical stimulation - when more is less

This study was conducted to determine whether electrical stimulation per se can be omitted when other electrical inputs to beef carcasses (stunning and immobilisation) are used. In addition, we investigated which sample preparation method at 1 day post mortem (p.m.), cooked fresh, frozen, or after thawing, had the best predictive value for shear force after ageing of the muscle. Beef carcasses were electrically immobilized (75 V, 15 Hz) before and during exsanguination for 20 or 80 s and meat quality characteristics of the longissimus were determined at 1 and 7 days post mortem. Muscles from carcasses receiving the higher electrical input were similar in tenderness at 1 day p.m., but tougher at 7 days p.m. This result could be explained by the effect of muscle shortening and post mortem proteolysis on tenderness. These results indicate that even low electrical input during immobilization can adequately stimulate carcasses and avoid cold shortening. Freezing samples resulted in a considerable improvement in tenderness and cooking samples from the frozen state had the highest predictive value for tenderness after ageing. In a second experiment it was determined that freezing and thawing did not result in appreciable differences in cooking loss or proteolysis. The tenderising effect of freezing may be explained by tissue damage due to ice formation.     

优质鸡肉质性状相互关系的研究

本试验研究了优质鸡胸肌和腿肌肌肉性状间的相互关系,并对肉质性状进行了主成分分析。结果表明,肌肉IMF与pH1、pH2、肌纤维密度呈正相关,而与烹饪损失、肌肉剪切力、肌纤维直径呈负相关。肌肉pH与烹饪损失、剪切力、肌纤维直径呈负相关,而与肌纤维密度呈极显著正相关。滴水损失与烹饪损失、肌纤维密度呈负相关,而与剪切力、肌纤维直径呈正相关。肌肉烹饪损失、剪切力与肌纤维直径呈正相关,而与肌纤维密度呈显著负相关。另外,主成分分析表明,胸肌肉质性状可以用4个主成分因子进行表示,腿肌肉质性状可以用2个主成分因子进行表示。     

Effects of ageing and cooking on the tenderness of beef muscle

When beef sternomandibularis muscle was subjected to prolonged cooking, toughness, measured by shearing force across the grain, was reduced by about 50%. The shortened state of the muscle determined the final shear-force value attained as in normal cooking, being considerably higher in meat at 40% shortening, than in either unshortened meat or in meat shortened by 60%. The tenderising effect of ageing was additional to that from long cooking. Ageing reduced the tensile strength of the myofibrils as measured by resistance to the shearing stresses of homogenisation. Cooking tenderising resulted from a breakdown in the collagen of the interstitial connective tissue. In cooked meat distinct linkages were shown to exist between Z-lines of adjacent myofibrils. The mechanical strength of cooked meat is ascribed to the tensile strength of the fibrous components of muscle and these lateral linkages.     

Effect of freezing on sensory quality, shear force and water loss in beef M. longissimus dorsi

The objective of this study was to determine how sensory quality, shear force and water loss differ between beef stored either chilled or frozen before cooking. Meat tenderness was analysed instrumentally and sensorially using both a consumer panel and a semi-trained panel. Both M. longissimus dorsi (LD) from eight young Holstein bulls were cut into eight samples, weighed, vacuum packed and aged at 4 °C for 2, 7 or 14 days. After ageing, the frozen samples were kept at −20 °C prior to heat treatment. Water holding capacity was recorded as purge or thawing loss and cooking loss or as combined loss. Sensory analyses were performed on samples aged 7 days. Peak force values declined with ageing time and freezing. Frozen meat aged 2 days had the same peak force values as chilled meat aged 7 days. Total energy was the same for both treatments at day 2 and 7, whereas at day 14 frozen samples showed significantly higher values than chilled samples. The sensory panel experienced the chilled meat to be more tender, juicier and having a more intense meat taste than the frozen meat, whereas the consumers could not find any significant difference in degree of liking. Water holding capacity was lower for the frozen samples. The results indicate that conclusions from studies concerning sensory quality of beef will depend on whether the meat has been kept chilled or frozen before testing.     

Postmortem changes in muscle electrical properties of bovine M. longissimus dorsi and their relationship to meat quality attributes and pH fall

Heifers (n=47) were slaughtered and hung conventionally in an industrial meat plant. Electrical impedance (Py) and conductivity (EC) were studied for their ability to indicate or predict selected meat quality attributes i.e. Warner-Bratzler shear force (WBSF), sensory tenderness, texture, flavour and acceptability, water holding capacity (WHC) and colour. pH, electrical impedance (meat check) and electrical conductivity (pork quality meter) measurements were taken at hourly intervals up to 8 h and again at 1 and 2 days postmortem. Electrical measurements were taken again at 7 and 14 days postmortem. Freshly cut steaks (2.5 cm thick) were taken from the longissimus dorsi (LD) muscle at 2, 7 and 14 days postmortem, vacuum-packaged in plastic bags and stored at -20°C for WBSF and sensory analysis. Freshly cut steaks were used for WHC and colour measurements. During the development of rigor and over the ageing period, electrical changes occur in muscle tissue. Electrical measurements were found to change significantly between 1 and 14 days postmortem and when measured over the ageing period (at 2, 7 and 14 days postmortem) were significantly correlated to WBSF, sensory tenderness and Hunter 'a' and 'b' values (r=±0.56-±0.68, p<0.001) and weakly to moderately correlated to other sensory attributes (r=±0.31-0.58, p<0.001) measured at the same times postmortem; thus showing potential for these rapid physical measurements as indicators of meat quality if both electrical measurements and quality attributes are measured at the same times postmortem and correlations are calculated over the ageing period. However, electrical measurements taken at specific times at the early postmortem period (i.e. at 1 or 2 days) showed only a few weak relationships with meat quality attributes measured at later times postmortem (i.e. 7 or 14 days) demonstrating that early postmortem electrical measurements are not suitable for the prediction of ultimate meat quality. Py values taken between 7 h and 7 days postmortem were significantly correlated with all pH measurements with the exception of 1 day values. Two day Py measurements showed the highest correlations (r=0.45-0.62, p<0.01-0.001) with pH. EC was also found to be moderately correlated with pH although correlations were slightly lower than those obtained for Py. Highest correlations (r=0.47-0.59, p<0.01) were obtained for 7 h values.     

宰后成熟时间对不同年龄牦牛肉用品质的影响

研究宰后成熟时间对不同年龄牦牛肉用品质（pH值、肉色、肌红蛋白含量、剪切力、失水率、蒸煮损失率）的影响,并分析成熟时间、年龄与肉用品质之间的相关性。结果表明：宰后成熟过程中,不同年龄牦牛肉L*值和b*值随着成熟时间的延长先上升后下降,而a*值先下降后上升;肌红蛋白含量随着成熟时间的延长而降低;pH值在成熟的前3 d发生了显著的变化（P＜0.05）,成熟过程中不同年龄牦牛肉pH值没有显著差异（P＞0.05）;失水率和蒸煮损失率在宰后成熟的第3天时达到最大;成熟3 d后,剪切力值显著降低（P＜0.05）;年龄与牦牛肉用品质指标均呈正相关,而成熟时间与L*值、b*值、失水率、蒸煮损失率呈较强的正相关,与剪切力、肌红蛋白含量呈显著负相关（P＜0.05）;牦牛宰后经过7 d的成熟,可以降低因屠宰年龄不同而产生的差异,同时也可以改善肉的嫩度。     

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

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

Skeletal muscle fiber type and myofibrillar proteins in relation to meat quality

Although numerous studies have reported the relationships among muscle fiber characteristics, lean meat content and meat quality, controversial perspectives still remain. Conventional histochemical classifications may be involved in a high level of error, subjectivity and it could not clearly explain variety of myofibrillar protein isoforms. Therefore, more information is needed on how different factors, such as species, breeds, gender, nutrient conditions, physiological state of animals, and environment factors, affect ultimate meat quality in order to evaluate these uncertainness. Unfortunately, there is little information that completely covers with relationship among the muscle fiber types, myofibrillar proteins and enzymatic proteolysis. In addition to the perspective of postmortem metabolism, protein quality control in skeletal muscle and proteolytic degradation of muscle proteins during postmortem period could help to clarify this relationship. Therefore, the present review will focus on muscle fiber types, typing methods, muscle proteins and meat quality, and will summarize aspects of enzymatic view of proteasome.     

Meat quality and cooking attributes of thawed pork with different low field NMR T(21)

A relationship of low field NMR T(2) components to meat quality and cooking attributes of pork was investigated. Longissimus muscle was removed from 23 pig carcasses at 24h postmortem for meat quality measurements and cooking test. Frozen samples were classified into three groups by LF-NMR T(21) of thawed samples: A (<40ms), B (40-44ms) and C (>44ms). There were significant differences (P<0.05) in pH, lightness (L* value) and pressing loss among the three groups. Cooking time to attain 70°C was slightly lower in group C than the other groups. Shear force value of cooked samples was not affected by T(21). The component T(21) correlated (P<0.05) with L* value, muscle pH and pressing loss, while L* value correlated (P<0.05) with thawing loss and muscle pH. Therefore, combined LF-NMR and color measurements could be a good way to differentiate water holding capacity of pork.     

Tenderness of pre- and post rigor lamb longissimus muscle

Lamb longissimus muscle (n=6) sections were cooked at different times post mortem (prerigor, at rigor, 1dayp.m., and 7 days p.m.) using two cooking methods. Using a boiling waterbath, samples were either cooked to a core temperature of 70 °C or boiled for 3h. The latter method was meant to reflect the traditional cooking method employed in countries where preparation of prerigor meat is practiced. The time postmortem at which the meat was prepared had a large effect on the tenderness (shear force) of the meat (P<0.01). Cooking prerigor and at rigor meat to 70 °C resulted in higher shear force values than their post rigor counterparts at 1 and 7 days p.m. (9.4 and 9.6 vs. 7.2 and 3.7 kg, respectively). The differences in tenderness between the treatment groups could be largely explained by a difference in contraction status of the meat after cooking and the effect of ageing on tenderness. Cooking pre and at rigor meat resulted in severe muscle contraction as evidenced by the differences in sarcomere length of the cooked samples. Mean sarcomere lengths in the pre and at rigor samples ranged from 1.05 to 1.20 μm. The mean sarcomere length in the post rigor samples was 1.44 μm. Cooking for 3 h at 100 °C did improve the tenderness of pre and at rigor prepared meat as compared to cooking to 70 °C, but not to the extent that ageing did. It is concluded that additional intervention methods are needed to improve the tenderness of prerigor cooked meat.