The influence of high temperature, type of muscle and electrical stimulation on the course of rigor, ageing and tenderness of beef muscles

The Quality Changes and Proteomic Analysis of Cattle Muscle Postmortem during Rigor Mortis

Rigor mortis occurs in a relatively early postmortem period and is a complex biochemical process in the conversion of muscle to meat. Understanding the quality changes and biomarkers during rigor mortis can provide a theoretical basis for maintaining and improving meat quality. Herein, a tandem mass tag proteomic method is used to investigate the effects of differentially expressed proteins on the meat quality of cattle Longissimus lumborum muscle postmortem (0, 6, and 24 h). The pH, total sulfhydryl content and sarcomere length decrease significantly during storage. In contrast, meat color values (L*, a*, and b*) and the myofibril fragmentation index increase significantly. Altogether, 147 differentially expressed proteins are identified, most being categorized as metabolic enzymes, mitochondrial proteins, necroptosis and ferroptosis proteins and structural proteins. The results also reveal additional proteins that are potentially involved in rigor mortis, such as cardiac phospholamban, acetyl-coenzyme A acyltransferase, and ankyrin repeat domain 2. The current results provide proteomic insights into the changes in meat quality during rigor mortis.

Resistance to pH decline and slower calpain-1 autolysis are associated with higher energy availability early postmortem in Bos taurus indicus cattle

Beef from Bos taurus indicus is associated with toughness compared to Bos taurus taurus, suggesting there is antagonism between adaptability to heat and beef quality. Resistance to cellular stress in muscle may be protective postmortem, thereby delaying its conversion to meat. Therefore, our objective was to determine pH decline, calpain-1 and caspase 3 activation, and proteolysis in different biological cattle types. Angus, Brangus, and Brahman steers (n = 18) were harvested, and Longissimus lumborum were assessed postmortem for pH decline, ATP content, protease activation, and calpastatin content; and myofibrillar protein degradation was evaluated in beef aged to 14d. Brahman Longissimus lumborum exhibited resistance to pH decline, greater ATP content at 1 h, and delayed calpain-1 autolysis. Although content of caspase-3 zymogen was lower in Brahman, there was no evidence of caspase-3 mediated proteolysis. Greater resistance to energetic and pH changes early postmortem in Brahman Longissimus lumborum are associated with calpain-1 autolysis but not mitochondria mediated apoptosis.

Volatile Flavor Components as a Function of Electrical Stimulation and Chiller Aging for m. longissimus and biceps femoris of Hanwoo Beef

The aim of the study was to evaluate the effect of an early post-mortem low voltage electrical stimulation (ES) to localized part of carcasses [m.longissimus lumborum (LL) and m.biceps femoris (BF)] and determined the tenderness and flavor compounds of Hanwoo steers (n=16). Carcasses were stimulated within 30 min post-mortem for 60s using 60 volts and muscles aged 2 and 14 d. Degradation of Troponin-T were accelerated by ES and degraded little faster in BF muscle than LL. Level of free amino acid content of stimulated and aged muscles was significantly (p<0.05) greater than control for both muscles. Totally 63 volatile compounds were identified by using SPME-GC. The ES treatment significantly (p<0.05) affected the level of 20 volatile compounds of LL as well 15 volatiles in BF muscle along with total amounts of ketones, sulfur containing, pyrazines and furans. Low voltage ES could be applied to reduce the aging time and improve volatile flavor development by increasing important desirable volatile compounds such as 2-methylpyrazine, 2,5-dimethylpyrazines and 2-acetylthiazole etc. due to released free amino acids from protein degradation.

Effects of electrical stimulation and pre-rigor conditioning temperature on aging potential of hot-boned beef M. longissimus lumborum

The objective of this study was to create various pH/temp decline rates in hot-boned bull beef M. longissimus lumborum (LL) through a combination of electrical stimulation (ES) and pre-rigor holding temperature. The relationship between the pre-rigor interventions, the activities of µ-calpain and small heat shock proteins (sHSP), and the impacts on meat product quality were determined. Paired LL loins from 13 bulls were hot-boned within 40 min of slaughter, immediately ES and subjected to various holding temperatures (5, 15, 25, and 35°C) for 3 hr. The rate of muscle pH decline, sarcomere length, shear force, and proteolysis of muscle proteins were measured. ES-25°C had a longer sarcomere length compared to non-electrical stimulation samples. ES-25°C and ES-35°C samples had lower shear force values, higher µ-calpain activity and higher desmin, troponin-T, and sHSP degradation. The above findings suggest that pH/temp decline rates created in hot-boned muscle impacted muscle protein proteolysis by increasing the activity of proteases and degradation of sHSP.

Mechanical and Biochemical Methods for Rigor Measurement: Relationship with Eating Quality

Meat quality parameters are affected by a complex series of interacting chemical, biochemical, physical, and physiological components that determine not only the suitability for consumption and the conditions for further processing and storage but also consumer acceptability. Deep understanding and careful manipulation of these intrinsic and extrinsic factors have to be taken in account to ensure high quality of meat, with better technological properties and increased safety for consumers. Among meat quality characteristics, meat tenderness has been perceived as the most important factor governing consumer acceptability. Therefore, being able to early predict meat texture and other related parameters in order to guarantee consistent eating quality to the final consumer is one of the most sought-after goals in the meat industry. Accurate measurements of both the biochemical and mechanical characteristics that underpin muscle and its transformation into meat are key factors to an improved understanding of meat quality, but also this early-stage measurements may be useful to develop methods to predict final meat texture. It is the goal of this review to present the available research literature on the historical and contemporary analyses that could be applied in early postmortem stages (pre-rigor and rigor) to determine the biochemical and physical characteristics of the meat that can potentially impact the eating quality.

Effect of Proteolytic Enzymes and Ginger Extract on Tenderization of M. pectoralis profundus from Holstein Steer

The effects of proteolytic enzymes (bromelain and bromelain+papain) and a ginger extract were assessed on collagen content and solubility, thermal shrinkage temperature of connective tissue, pH, cooking loss, drip loss, and Warner-Bratzler shear force (WBSF) of M. pectoralis profundus isolated from the beef brisket cut. Both proteolytic enzymes and ginger extract led to a significant increase in cooking loss and collagen solubility compared with untreated controls. On the other hand, the peak (T_p) thermal shrinkage temperature markedly decreased in all treatments compared with those in controls. Samples treated with bromelain, bromelain + papain, and ginger extract showed a significant decrease in WBSF by 36%, 40%, and 37%, respectively, compared with untreated controls. Our findings suggest that ginger extract are useful for postmortem tenderization of meat containing high levels of collagen, compared to control even though, bromelain and bromelain + papain treatments have higher collagen solubility than ginger extract.

Variation in instrumental meat quality among 15 muscles from 14-month-old sheep and its relationship with fibre typing

The aims of the present study were to describe intermuscular differences in meat-quality traits in 15 young-sheep muscles, and to study the associations between meat quality and fibre typing across all (pooled) muscles as well as in previously selected homogeneous contractile–metabolic groups of muscles (slow-oxidative, intermediate and fast-glycolytic muscles). Meat-quality traits (pH, colour, expressed juice, cooking losses, tenderness and sarcomere length) and fibre typing were evaluated after 24 h of slaughter in 15 muscles from five cross-bred young sheep. Across all the studied muscles, intermuscular differences in some meat-quality traits (pH24, a* and expressed juice) seemed to be mainly explained by muscle oxidative activity, while intermuscular variation in other meat-quality traits (L*, b* and Warner–Bratzler shear force) were mainly explained by differences in fibre sizes. Within fast-glycolytic muscles, larger fast-glycolytic fibres and reduced oxidative activity were generally associated with lower ultimate pH, higher L* values, lower a* values and longer sarcomeres. Within intermediate muscles, larger fast-glycolytic fibres and reduced oxidative activity were generally associated with lower ultimate pH, higher L* values, shorter sarcomeres and reduced meat tenderness. Within slow-oxidative muscles, larger fast-glycolytic fibres and reduced oxidative activity were generally associated with lower amounts of expressed juice, lower a* values and reduced meat tenderness. The present study has contributed to a better understanding of the influence of muscle fibre types on intermuscular meat-quality variation, suggesting that although muscle fibre diversity may explain, at least in part, intermuscular differences in meat quality, these associations can also slightly vary among muscle contractile–metabolic groups.

Monitoring microstructural variations of fresh skeletal muscle tissues by Mueller matrix imaging

Recently many attempts have been made for extracting the structural information of myofibrils as indicators for diseases of skeletal muscle. In this paper we adopt wide-field illumination and take the backscattering Mueller matrix images of bovine skeletal muscle tissues during the 24-hour experimental time after the animal's death. The 2D images of Mueller matrix elements and their frequency distribution histograms (FDHs) reveal rich qualitative information on the changes in the microstructures of the skeletal muscle. The temporal variations of the sample are quantitatively analyzed using two Mueller matrix transformation (MMT) parameters. The characteristic features of the temporal plots are attributed to the rigor mortis and proteolysis processes. For a deeper insight on the relationship between the features of the MMT parameters and the microstructures during the rigor mortis and proteolysis processes, Monte Carlo (MC) simulations are carried out based on sphere-cylinder birefringence model (SCBM). The good agreement between the experimental and MC simulated results show that the FDHs and MMT parameters can describe more clearly the characteristic microstructural features of skeletal muscle tissues. The techniques are useful for the characterization of physiological status of tissues, or quantitative assessment of meat qualities in food industry.

The influence of post-mortem conditioning on the tenderness of Egyptian goose (Alopochen aegyptiacus) breast meat (M. pectoralis major)

BACKGROUND

Egyptian goose breast meat has been found to be very tough compared to the meat of other well-known fowl species. In attempting to clarify the toughness of the meat, the physical and biochemical changes during post-mortem conditioning (14 days) was investigated.

RESULTS

Although there was increased cathepsin (B, B & L and H) activity, together with a decrease (P ≤ 0.05) in myofibrillar fragmentation lengths (32-25 µm) with conditioning, no change (decline) in shear force values was observed. The higher (P ≤ 0.05) shear force of the male breast portions may be linked to the higher (P ≤ 0.05) concentrations of total and insoluble collagen.

CONCLUSIONS

No significant change (decline) in shear force values was observed. Conditioning of Egyptian goose meat as a means of improving the overall toughness cannot therefore not be proposed. The higher shear force and lower sensory tenderness of the male breast portions, as previously observed, may be linked to higher concentrations of total and insoluble collagen.

Post mortem rigor development in the Egyptian goose (Alopochen aegyptiacus) breast muscle (pectoralis): factors which may affect the tenderness

BACKGROUND

Baseline research on the toughness of Egyptian goose meat is required. This study therefore investigates the post mortem pH and temperature decline (15 min-4 h 15 min post mortem) in the pectoralis muscle (breast portion) of this gamebird species. It also explores the enzyme activity of the Ca(2+)-dependent protease (calpain system) and the lysosomal cathepsins during the rigor mortis period.

RESULTS

No differences were found for any of the variables between genders. The pH decline in the pectoralis muscle occurs quite rapidly (c = -0.806; ultimate pH ∼ 5.86) compared with other species and it is speculated that the high rigor temperature (>20 °C) may contribute to the increased toughness. No calpain I was found in Egyptian goose meat and the µ/m-calpain activity remained constant during the rigor period, while a decrease in calpastatin activity was observed. The cathepsin B, B & L and H activity increased over the rigor period.

CONCLUSION

Further research into the connective tissue content and myofibrillar breakdown during aging is required in order to know if the proteolytic enzymes do in actual fact contribute to tenderisation.

Effect of rigor temperature, ageing and display time on the meat quality and lipid oxidative stability of hot boned beef Semimembranosus muscle

The effects of rigor temperature (5, 15, 20 and 25°C), ageing (3, 7, 14, and 21 days) and display time on meat quality and lipid oxidative stability of hot boned beef M. Semimembranosus (SM) muscle were investigated. Ultimate pH (pH(u)) was rapidly attained at higher rigor temperatures. Electrical conductivity increased with rigor temperature (p<0.001). Tenderness, purge and cooking losses were not affected by rigor temperature; however purge loss and tenderness increased with ageing (p<0.01). Lightness (L*) and redness (a*) of the SM increased as rigor temperature increased (p<0.01). Lipid oxidation was assessed using (1)H NMR where changes in aliphatic to olefinic (R(ao)) and diallylmethylene (R(ad)) proton ratios can be rapidly monitored. R(ad), R(ao), PUFA and TBARS were not affected by rigor temperature, however ageing and display increased lipid oxidation (p<0.05). This study shows that rigor temperature manipulation of hot boned beef SM muscle does not have adverse effects on lipid oxidation.

Regulation of post-mortem glycolysis in ruminant muscle

As a tissue, muscle has the unique ability to switch its metabolic source of ATP, the energy currency underpinning muscle function. During oxygen debt, such as that occurring immediately following the death of animals, anaerobic metabolism is initiated in an attempt to restore homeostasis within the muscle. The cascade of biochemical events that are initiated is paramount in the context of meat quality. This review revisits this reasonably well-known subject but takes a new perspective by drawing on the understanding outside the traditional discipline of meat science. Our understanding of the intrinsic regulators of glycolytic flux has improved but knowledge gaps remain. Further efforts to understand how the glycolytic enzyme kinetics are influenced by both pre- and post-slaughter factors will be beneficial in the ongoing quest to maximise fresh meat quality.

Pre-rigor carcass stretching counteracts the negative effects of high rigor temperature on tenderness and water-holding capacity – using lamb muscles as a model

High pre-rigor muscle temperature has negative consequences on quality and has been predominantly studied in the excised longissimus muscle of beef and lamb carcasses. There is little data on other muscles, the application in whole carcasses or potential amelioration techniques such as stretching. This study evaluated the effects of electrical stimulation, high pre-rigor temperature and stretching of lamb sides on quality traits and protein denaturation in four leg muscles [gluteus medius (GM), rectus femoris (RF), semimembranosus (SM) and semitendinosus (ST)]. Twenty lamb carcasses were used with two electrical stimulation treatments (stimulated or non-stimulated, +/−) and two pre-rigor temperature treatments (chilled at 2°C directly after slaughter, or held in 37°C water for 4.5 h before transfer to a 2°C chiller) applied. One side of each carcass was suspended from the Achilles tendon, whereas the other side was stretched by allowing the leg to drop and tying it to the ribs. Electrical stimulation did not influence the different traits except for pH fall post slaughter and myosin denaturation. Stretching resulted in greater muscle and sarcomere lengths for the GM, SM and ST, but a decrease in sarcomere length for the RF. For the non-stretched GM and SM, the 37°C treatment resulted in tougher meat at 1 and 8 days post mortem compared with the 2°C treatment. In contrast, the stretched 37°C treatment resulted in more tender meat for the GM, SM and ST at 1 day post mortem compared with the 2°C treatment. For all muscles, the 37°C treatment resulted in a decrease in the water-holding capacity (increased purge, surface exudate and cooking losses). The magnitude of this effect was generally diminished by stretching for the GM, SM and ST, but for the RF, (which was not stretched by the treatment) this effect was reversed. The 37°C treatment resulted in paler meat (increased L*-values) for the GM, SM and ST relative to the 2°C treatment. The observed effects of the 37°C treatment on water-holding capacity and colour could be explained by the effects of this treatment on indicators of protein denaturation (sarcoplasmic protein solubility and myofibrillar ATPase activity), which were decreased for the GM, SM and ST. The response to both temperature and stretching varied between the muscles, due to different anatomical location and also due to postulated differences in the fibre types. In conclusion, pre-rigor stretching of lamb sides can counteract the negative effects of high early post-mortem temperature on tenderness and water-holding capacity for those muscles that are stretched as a result of this hanging method.

Influence of high pre-rigor temperature and fast pH fall on muscle proteins and meat quality: a review

The impacts of accelerated pH decline combined with high muscle temperature on post-mortem muscle metabolism and subsequent meat quality attributes have been extensively studied. Traditionally, this phenomenon has been observed in pork muscles, primarily due to the relatively fast post-mortem glycolysis rate and its relationships to stress susceptibility of pigs before slaughter. However, the protein-denaturing condition of high temperature/rapid pH fall and subsequent PSE (pale, soft and exudative)-like abnormal meat quality characteristics have been observed in muscles from other species such as beef, lamb, venison and even poultry. Various pre-rigor conditions including the application of electrical stimulation, hot-boning, and/or pre-rigor carcass chilling temperatures in various muscles, in conjunction with carcass stretching/hanging methods, can also contribute to muscle-protein denaturation pre-rigor. This review considers the influence of a faster than normal pH fall at a higher than normal pre-rigor temperature on glycolysis, post-mortem muscle proteins and subsequently meat quality attributes. Gaps in current knowledge are identified and recommendations made for additional research.

Techniques to reduce the temperature of beef muscle early in the post mortem period – a review

A review of the literature was conducted on the effects of high temperature and low pH (HTLP) on meat quality, with a focus on interventions that increase the rate of cooling post slaughter. HTLP can potentially change meat tenderness, water-holding capacity and colour due primarily to protein denaturation during the first 5 h post mortem. Deep muscles in large carcasses are susceptible to HTLP when cooled conventionally. Ante mortem and post mortem solutions that increase the rate of carcass cooling are discussed. Ante mortem solutions include access to feed and water, showering with water and provision of shade. Post mortem solutions included vascular flushing, hot fat trimming, opening seams, hot boning, spray chilling, blast chilling, immersion cooling, and very fast chilling. Accelerating rigor with electrical stimulation before HTLP remains controversial. Combinations of different techniques, that suit the specific requirements of a particular processing plant, is the likely best solution to HTLP, but further development of commercial solutions is suggested.

Effect of low voltage electrical stimulation on protein and quality changes in bovine muscles during postmortem aging

This experiment was conducted to determine the influence of low voltage electrical stimulation (ES) on the tenderness development of beef round muscles. Eight steers were slaughtered, and ES applied to one side of each carcass within 90 min of exsanguination. Steaks from M. longissimus dorsi, semimembranosus, adductor, and gracilis were vacuum packaged and aged at 4 °C for 9 d. Star probe, sensory evaluation, Western blot assays of troponin-T and μ-calpain autolysis and 2D-DIGE were conducted. ES resulted in accelerated (P<0.05) pH decline of the longissimus in the first 24h postmortem. ES did not influence (P>0.05) proteolysis and tenderness, but did alter the predominance of metabolic proteins in the soluble fraction of muscle. Aging for 9 d improved tenderness (P<0.05). The data confirmed that low voltage ES at 90 min of exsanguination had no effect on proteolysis and tenderness development in the longissimus dorsi, semimembranosus, adductor or gracilis in beef.

Effect of pre-rigor stretch and various constant temperatures on the rate of post-mortem pH fall, rigor mortis and some quality traits of excised porcine biceps femoris muscle strips

Porcine biceps femoris strips of 10 cm original length were stretched by 50% and fixed within 1 hr post mortem then subjected to temperatures of 4 °, 15 ° or 36 °C until they attained their ultimate pH. Unrestrained control muscle strips, which were left to shorten freely, were similarly treated. Post-mortem metabolism (pH, R-value) and shortening were recorded; thereafter ultimate meat quality traits (pH, lightness, extraction and swelling of myofibrils) were determined. The rate of pH fall at 36 °C, as well as ATP breakdown at 36 and 4 °C, were significantly reduced by pre-rigor stretch. The relationship between R-value and pH indicated cold shortening at 4 °C. Myofibrils isolated from pre-rigor stretched muscle strips kept at 36 °C showed the most severe reduction of hydration capacity, while paleness remained below extreme values. However, pre-rigor stretched myofibrils - when stored at 4 °C - proved to be superior to shortened ones in their extractability and swelling.

Ultra-fast freezing and low storage temperatures are not necessary to maintain the functional properties of manufacturing beef

The effects of freezing rates and subsequent storage temperatures on the functional properties of meat were assessed. In the first trial, 24 Semitendinosus muscles were allocated to four freezing treatments to determine the effect of freezing rate alone (no frozen storage) on the functional properties of thawed muscle proteins. In the second trial, the effect of freezing rate, storage temperature and time were determined: 24 semimembranosus muscles were assigned to 30 treatment combinations using an incomplete factorial design with two freezing rates × three storage temperatures × five storage times. All samples individually sealed in water impermeable bags were thawed in water at 10 °C and then analysed. The rate of freezing alone in both trials and for both muscles had no effect on protein solubility; sulphydryl content; surface hydrophobicity; emulsion activity index or meat colour. Slowly frozen semimembranosus had more drip than fast frozen muscles. Semimembranosus muscle sarcoplasmic protein solubility increased and myofibrillar protein solubility decreased with storage temperature below -18 °C. Storage temperature did not affect the other attributes measured. Functional properties were mainly affected by storage time and the interaction between storage time and freezing rate. It is concluded that the current practice of blast freezing and storage at -18 to 20 °C is sufficient to maintain the quality of manufacturing beef.

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

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

miRNA-dysregulation associated with tenderness variation induced by acute stress in Angus cattle

miRNAs are a class of small, single-stranded, non-coding RNAs that perform post-transcriptional repression of target genes by binding to 3’ untranslated regions. Research has found that miRNAs involved in the regulation of many metabolic processes. Here we uncovered that the beef quality of Angus cattle sharply diversified after acute stress. By performing miRNA microarray analysis, 13 miRNAs were significantly differentially expressed in stressed group compared to control group. Using a bioinformatics method, 135 protein-coding genes were predicted as the targets of significant differentially expressed miRNAs. Gene Ontology (GO) term and Ingenuity Pathway Analysis (IPA) mined that these target genes involved in some important pathways, which may have impact on meat quality and beef tenderness.

Muscle transcriptomic analyses in Angus cattle with divergent tenderness

Beef tenderness contributes significantly to variation of beef palatability, and is largely influenced by various genetic and environmental factors. To identify candidate genes and pathways related to beef tenderness, we analyzed the longissimus dorsi (LD) muscle of Angus cattle that had different degrees of tenderness, measured by Warner-Bratzler shear force (WBSF). Microarray and RT-PCR analyses identified 53 genes that were differentially expressed in LD samples categorized as either tough or tender, including myosin, heavy chain 3 skeletal muscle embryonic (MYH3), myosin heavy chain 8 skeletal muscle perinatal (MYH8), guanylate binding protein 5 (GBP5), fatty acid binding protein 4 (FABP4), Stearoyl-coenzyme A desaturase (SCD), Fatty acid synthase (FASN), ubiquitin-like with PHD and ring finger domains 1 (UHRF1). Most of these genes are involved in lipid metabolism and skeletal muscle contraction. Employing Gene ontology (GO) and Ingenuity Pathway Analysis (IPA), several GO terms and pathways were found to be related to hydrolase, peptidase and GTPase activity, lipid metabolism, small molecule biochemistry, molecular transport, and tissue development. Overall, this analysis provides insight into the metabolic relationships between muscle biology and beef quality.

Length of exposure to high post-rigor temperatures affects the tenderisation of the beef M. longissmus dorsi

This experiment examined the effect of length of exposure of bovine M. longissmus dorsi to high temperatures (37°C) on proteolytic activity during post-mortem aging and subsequent meat tenderness. To avoid confounding between pH decline and incubation treatments, the experiment was conducted on post-rigor meat (pH < 5.6), which had entered rigor at 15°C. This meat was first incubated at 15°C until rigor (pH < 5.6), whereupon samples were then reheated and maintained at 37°C for 0, 1 or 3 h. Following incubation, samples were aged at 1°C for 1–21 days. Control groups were incubated at either 15 or 37°C until pH < 5.6, followed by aging at 1°C. High rigor temperatures accelerated post-mortem proteolysis early in the post-mortem period, as indicated by a rapid decline in shear force (P < 0.01), but post-mortem aging ceased at about day 3 post-mortem and the high rigor temperature treatment was ultimately 30% tougher at day 21 post-mortem (P < 0.01). The process of reheating samples from 15 to 37°C had minimal effect on tenderness levels, but was associated with a slight increase in proteolysis, identified by myofibril length, and was associated with an increase in cook loss percentage (P < 0.05). Shear force in the length of exposure experiment was affected by an incubation time × post-mortem aging interaction (P < 0.01). This indicated an initial acceleration of post-mortem aging with increased length of exposure, but also a reduction in the ultimate tenderness of product after extended post-mortem aging. This was presumably due to the loss of proteolytic enzyme activity caused by the instability of proteolytic enzymes at high ionic strength conditions such as those present in post-mortem muscle.

Development of a commercial system to apply the Meat Standards Australia grading model to optimise the return on eating quality in a beef supply chain

A major trial was conducted to develop, test and demonstrate the application of Meat Standards Australia (MSA) research findings in a beef retailing environment. A new concept retail store was established whereby a mix of raw beef products and pre-cooked meals were merchandised under an eating quality grade defined by MSA palatability scores. Products were presented fully prepared within cooking method with pricing based on the predicted cooked results. Large price differentials were established between the three grades offered, with 5-star product priced at more than double the 3-star product. The principle of pricing being directly related to eating quality was extended from the retail store sales to fabrication and the purchase of source cattle from producers. This encouraged considerable innovation to optimise eating quality and returns, demonstrating the potential for truly transparent value-based pricing systems to achieve change. Novel systems were developed to break down and fabricate the carcass into ‘retail-ready’ product with extensive software development to trace the eating quality, value and location of individual cuts and products. Detailed feedback provided the producer with an accurate measure of value and sufficient data to evaluate possible alternative production strategies. Results at each level of the supply chain were encouraging with compound annual growth in sales exceeding 12% at retail level and continued innovation through fabrication and on-farm areas combining to improve eating quality and financial outcomes. It was demonstrated that the consumer focus delivered by MSA grades could be applied at a commercial level providing an opportunity to reposition beef as a contemporary consumer product and to implement a value-based system across all sectors.

Imaging 2D optical diffuse reflectance in skeletal muscle

We discovered a unique pattern of optical reflectance from fresh prerigor skeletal muscles, which can not be described using existing theories. A numerical fitting function was developed to quantify the equiintensity contours of acquired reflectance images. Using this model, we studied the changes of reflectance profile during stretching and rigor process. We found that the prominent anisotropic features diminished after rigor completion. These results suggested that muscle sarcomere structures played important roles in modulating light propagation in whole muscle. When incorporating the sarcomere diffraction in a Monte Carlo model, we showed that the resulting reflectance profiles quantitatively resembled the experimental observation.

Critical control points for meat quality in the Australian sheep meat supply chain Critical control points for meat quality in the Australian sheep meat supply chain

The sheep meat eating quality research program has identified a number of outcomes and critical control points in the supply chain from live sheep genetics to cooked meat. The critical control points, which are largely independent of each other, can be translated into quality management systems to increase average eating quality of all cuts and lower variability. The choice of sire was a critical control point in that selecting for high growth rate and muscling can adversely affect eating quality. The challenge is to make sure that high yield traits are not promoted at the expense of eating quality. Animal age was a critical control point but it was clear that the definition of hogget could be revised to include slightly older animals with teeth in eruption but not in wear. Moreover, M. longissumus dorsi from older animals had only slightly lower eating quality than that from lamb such that this cut could be positioned as a premium product at all maturities, complementing the universally tender muscle psoas major. There was no doubt, however, that over all muscles, lamb remained the premium product. The critical control point for nutrition is that it be adequate, typically to ensure growth of at least 50 g/animal.day. Meat quality is improved through higher glycogen concentrations in muscles at slaughter, higher intramuscular fat content, and possibly reduced collagen crosslinking. Critical control points between muster and slaughter are more difficult to define but are generally aimed at stress reduction to minimise occurrence of the high ultimate pH condition. They include avoiding temperature extremes, loud noises and use of dogs, implementation of good lairage design and the use of skilled animal handlers. Stress is best monitored by ultimate pH measurements in abattoirs, rather than at remote points down the supply chain. After slaughter, the use of electrical stimulation to accelerate post mortem glycolysis is a critical control point. Its use is indicated where 2 conditions are simultaneously met: carcasses are Achilles-hung throughout processing, and the meat is destined for early consumption, as would normally be the case for the domestic market. By accelerating glycolysis, the temperature at rigor can be optimised for rapid tenderisation of low-connective tissue muscles through ageing. The alternative to electrical stimulation of these muscles for the local market is Tenderstretch hanging where rapid ageing is less temperature dependent. Where electrical stimulation is applied the monitoring of its effects with a temperature probe and a pH metre is a critical control point. Even where stimulation is not applied, measurement of average muscle temperature and pH is useful for defining any process. This is because the first 24 h after slaughter sets the scene for later meat storage/distribution, which has its own critical control point: the temperature at which meat is held between abattoir and consumption. Where meat is destined for early sale, the temperature of processing and storage can and should be higher than where the meat is destined for long-term storage as in export markets. For early sale, rapid ageing to optimum eating quality is promoted by higher temperature (2–4°C), whereas for export sale, very cool meat will slowly age in the weeks before consumption while at the same time minimising spoilage and maximising display life. Thus, matching the time–temperature profile of processing and storage to a particular market is a critical control point. The retail end of the supply chain has its own control points, principally display temperature and choice of display packaging, which have major effects on chilled display life. The cooler the better. Compared with conventional overwrap packs, modified atmosphere packs extend display life by typically 80%. However, these more sophisticated packs cost more and will not suit all domestic retailers. The matching of muscles by age with recommended cooking method is a critical control point at retail for ensuring consumer satisfaction. The challenge is effective communication with consumers and is part of the wider challenge of effectively communicating quality-related information at all links of the supply chain.