Factors determining the time course of rigor mortis

Meta-Regression Analysis of Relationships between Fibre Type and Meat Quality in Beef and Pork-Focus on Pork

This meta-regression analysis was conducted to identify the relationship between fibretype cross-sectional area (CSA) and frequency (%) and meat quality traits, especially tenderness (sensory and Warner-Bratzler Shear Force, WBSF). Literature searches were conducted using specific keywords which resulted in 32 peer-reviewed manuscripts that contained averages and correlation coefficients for fibre type (frequency and CSA) and quality traits of longissimus muscle for beef and pork (7 and 25 studies respectively). Correlations were analysed in meta-regression using R-Studio and linear regression was also conducted. For the combined beef and pork analysis, only pH, WBSF, and drip loss were associated with fibre type frequency and CSA (p < 0.05 for all). Limiting the analysis to pork, the key results were frequency of type I fibres were associated with decreased drip loss, increased cook loss, decreased lightness (L*) and increased sensory tenderness whereas frequency of type IIb fibres were associated with increased drip loss (p < 0.05 for all). In addition, the CSA of type I and IIb fibres was associated with colour traits lightness and redness (p < 0.05 for all). Future research should focus on fibre type across breeds and muscles to further understand the impacts of fibre type frequency and CSA on quality.

Postmortem submersion interval estimation of cadavers recovered from freshwater based on gut microbial community succession

Microbial community succession during decomposition has been proven to be a useful tool for postmortem interval (PMI) estimation. Numerous studies have shown that the intestinal microbial community presented chronological changes after death and was stable in terrestrial corpses with different causes of death. However, the postmortem pattern of intestinal microbial community succession in cadavers retrieved from water remains unclear. For immersed corpses, the postmortem submersion interval (PMSI) is a useful indicator of PMI. To provide reliable estimates of PMSI in forensic investigations, we investigated the gut microbial community succession of corpses submersed in freshwater and explored its potential application in forensic investigation. In this study, the intestinal microbial community of mouse submersed in freshwater that died of drowning or CO2 asphyxia (i.e., postmortem submersion) were characterized by 16S rDNA amplification and high-throughput sequencing, followed by bioinformatic analyses. The results demonstrated that the chronological changes in intestinal bacterial communities were not different between the drowning and postmortem submersion groups. α-diversity decreased significantly within 14 days of decomposition in both groups, and the β-diversity bacterial community structure ordinated chronologically, inferring the functional pathway and phenotype. To estimate PMSI, a regression model was established by random forest (RF) algorithm based on the succession of postmortem microbiota. Furthermore, 15 genera, including Proteus, Enterococcus, and others, were selected as candidate biomarkers to set up a concise predicted model, which provided a prediction of PMSI [MAE (± SE) = 0.818 (± 0.165) d]. Overall, our present study provides evidence that intestinal microbial community succession would be a valuable marker to estimate the PMSI of corpses submerged in an aquatic habitat.

Insights on meat quality from combining traditional studies and proteomics

Following a century of major discoveries on the mechanisms determining meat colour and tenderness using traditional scientific methods, further research into complex and interactive factors contributing to variations in meat quality is increasingly being based on data-driven "omics" approaches such as proteomics. Using two recent meta-analyses of proteomics studies on beef colour and tenderness, this review examines how knowledge of the mechanisms and factors underlying variations in these meat qualities can be both confirmed and extended by data-driven approaches. While proteomics seems to overlook some sources of variations in beef toughness, it highlights the role of post-mortem energy metabolism in setting the conditions for development of meat colour and tenderness, and also points to the complex interplay of energy metabolism, calcium regulation and mitochondrial metabolism. In using proteomics as a future tool for explaining variations in meat quality, the need for confirmation by further hypothesis-driven experimental studies of post-hoc explanations of why certain proteins are biomarkers of beef quality in data-driven studies is emphasised.

Cancer biology as revealed by the research autopsy

A research autopsy is a post-mortem medical procedure performed on a deceased individual with the primary goal of collecting tissue to support basic and translational research. This approach has increasingly been used to investigate the pathophysiological mechanisms of cancer evolution, metastasis and treatment resistance. In this Review, we discuss the rationale for the use of research autopsies in cancer research and provide an evidence-based discussion of the quality of post-mortem tissues compared with other types of biospecimens. We also discuss the advantages of using post-mortem tissues over other types of biospecimens, including the large amounts of tissue that can be obtained and the extent of multiregion sampling that is achievable, which is not otherwise possible in living patients. We highlight how the research autopsy has supported the identification of the clonal origins and modes of spread among metastases, the extent that selective pressures imposed by treatments cause bottlenecks leading to parallel and convergent tumour evolution, and the creation of rare tissue banks and patient-derived model systems. Finally, we comment on the future of the research autopsy as an integral component of precision medicine strategies.

Biomechanical Analysis of Porcine Cartilage Elasticity

Grafting of tissue-engineered cartilage to joints with osteoarthritis has the potential to supersede arthroplasty as the standard of care. However, in order to support the development of functional tissue engineering methods, the subfailure biomechanics of the individual cartilage types that comprise joints must be determined. Current methods for analyzing tissues are based on imaging and are therefore unable to profile the strain dependence of mechanical behaviors within different cartilage types. Recently, an analysis technique based on Optical Fiber Polarimetric Elastography (OFPE) has overcome these challenges. OFPE has been used to characterize the different mechanical behaviors of a range of unprocessed biomaterials and tissues. In the present work, this technique is used to characterize the biomechanics of both articular cartilage and meniscal fibrocartilage within a porcine knee. OFPE testing of the tissue is conducted over a range of physiological loading and unloading values. These results demonstrate the distinctive mechanics of each cartilage type. Due to their different locations within the knee, each cartilage type exhibits distinctly unique biomechanical behavior. Based on the results of OFPE, we correlate the specific buckling, delamination, and bridging events to maxima and minima along the loading and unloading curves. This provides unprecedented detail with regard to the subfailure biomechanics. This information is integral to the design of the next generation of tissue-engineered constructs. Therefore, OFPE will be used across multiple disciplines to rapidly determine the mechanical behavior of tissue-engineered constructs to support functional tissue engineering efforts.

Mechanical Analysis of the Uterosacral Ligament: Swine vs. Human

The uterosacral ligament (USL) is a major suspensory structure of the female pelvic floor, providing support to the cervix and/or upper vagina. It plays a pivotal role in surgical procedures for pelvic organ prolapse (POP) aimed at restoring apical support. Despite its important mechanical function, little is known about the mechanical properties of the USL due to the constraints associated with in vivo testing of human USL and the lack of validated large animal models that enable such investigations. In this study, we provide the first comparison of the mechanical properties of swine and human USLs. Preconditioning and pre-creep data up to a 2 N load and creep data under a 2 N load over 1200 s were obtained on swine (n = 9) and human (n = 9) USL specimens by performing planar equi-biaxial tensile tests and using the digital image correlation method. No differences in the peak strain during preconditioning tests, secant modulus of the pre-creep response, and strain at the end of creep tests were detected in the USLs from the two species along both axial loading directions (the main in vivo loading direction and the direction that is perpendicular to it). These findings suggest that the swine holds promise as large animal model for studying the mechanical role of the USL in apical vaginal support and treatment of POP.

The effect of ATP marination on the depolymerization of actin filament in goose muscles during postmortem conditioning

In order to study the tenderization mechanism of ATP treatments by depolymerizing actin filaments, breast muscles of Eastern Zhejiang White Geese were randomly divided into 3 groups: control, 10 and 20 mM groups. Shear force (SF), sarcomere length (SL) and myofibrillar fraction index (MFI), the content of F-actin and G-actin, the expression of actin associated proteins (cofilins and tropomodulins) were investigated during conditioning. In 20 mM group, cofilins content increased from 48 to 168 h, while tropomodulins decreased; the content of F-actin decreased from 24 to 168 h, while the increased G-actin was observed upto 48 h. In the control, the degraded tropomodulins were observed at 168 h, and the increased cofilins and G-actin were detected at the same time; the increase of MFI and decrease of F-actin content were shown at 96 and 168 h. Compared to control group, 20 mM group accelerated the transformation of F-actin into G-actin; it showed higher SL and MFI, and lower SF at 48, 96 and 168 h, respectively. We concluded that depolymerization of actin filaments, which was regulated by cofilins and tropomodulins, contributed to myofibrillar fraction and low SF during conditioning.

Role of extracellular matrix in the biomechanical behavior of pancreatic tissue

Correlating the biomechanical properties of tissue with its function is an emerging area of research with potential impact in diagnostics, therapeutics, and prognostics. A critical stepping-stone in developing structure-function models is creating methods that can correlate the tissue structure with its mechanical behavior. As an initial step in addressing this challenge, we have characterized the mechanical behavior of unprocessed pancreatic tissue using optical fiber polarimetric elastography. To correlate the observed behavior to physiologically relevant structural features, a series of architectures are designed and fabricated using 3D printing. The mechanical response of the 3D printed elastomeric structures is analyzed using compressive testing and modeled using finite element analysis. The biomechanical behavior and buckling point of the 3D printed structures is used to create a calibration curve to understand the measured response of the resected pancreatic tissue. Based on the modeling and biomimetic results, the biomechanical behavior of pancreatic tissue is likely due to the collagen IV network.

Differences in global gene expression in muscle tissue of Nellore cattle with divergent meat tenderness

Background

Meat tenderness is the consumer’s most preferred sensory attribute. This trait is affected by a number of factors, including genotype, age, animal sex, and pre- and post-slaughter management. In view of the high percentage of Zebu genes in the Brazilian cattle population, mainly Nellore cattle, the improvement of meat tenderness is important since the increasing proportion of Zebu genes in the population reduces meat tenderness. However, the measurement of this trait is difficult once it can only be made after animal slaughtering. New technologies such as RNA-Seq have been used to increase our understanding of the genetic processes regulating quantitative traits phenotypes. The objective of this study was to identify differentially expressed genes related to meat tenderness, in Nellore cattle in order to elucidate the genetic factors associated with meat quality. Samples were collected 24 h postmortem and the meat was not aged.

Results

We found 40 differentially expressed genes related to meat tenderness, 17 with known functions. Fourteen genes were up-regulated and 3 were down-regulated in the tender meat group. Genes related to ubiquitin metabolism, transport of molecules such as calcium and oxygen, acid-base balance, collagen production, actin, myosin, and fat were identified. The PCP4L1 (Purkinje cell protein 4 like 1) and BoLA-DQB (major histocompatibility complex, class II, DQ beta) genes were validated by qRT-PCR. The results showed relative expression values similar to those obtained by RNA-Seq, with the same direction of expression (i.e., the two techniques revealed higher expression of PCP4L1 in tender meat samples and of BoLA-DQB in tough meat samples).

Conclusions

This study revealed the differential expression of genes and functions in Nellore cattle muscle tissue, which may contain potential biomarkers involved in meat tenderness.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4323-0) contains supplementary material, which is available to authorized users.

Microbiome Tools for Forensic Science

Microbes are present at every crime scene and have been used as physical evidence for over a century. Advances in DNA sequencing and computational approaches have led to recent breakthroughs in the use of microbiome approaches for forensic science, particularly in the areas of estimating postmortem intervals (PMIs), locating clandestine graves, and obtaining soil and skin trace evidence. Low-cost, high-throughput technologies allow us to accumulate molecular data quickly and to apply sophisticated machine-learning algorithms, building generalizable predictive models that will be useful in the criminal justice system. In particular, integrating microbiome and metabolomic data has excellent potential to advance microbial forensics.

Comment on "Promising blood-derived biomarkers for estimation of the postmortem interval" by I. Costa, F. Carvalho, T. Magalhães, P. G. de Pinho, R. Silvestre & R. J. Dinis-Oliveira. (Toxicol. Res., 2015, , 1443-1452)

Recently, Costa et al. published an article about promising biomarkers for estimating the postmortem interval. Instead of postmortem blood, antemortem blood was putrefied in vitro by exposing the blood to a temperature gradient. However, in this way several other influencing factors were excluded, hence, the accuracy of the proposed model is doubtful. Therefore, the aim of this comment is to discuss the methodology, results and shortcomings of the study of Costa et al.

Optimisation of tenderisation, ageing and tenderness

Tenderness is an important part of meat acceptability and is affected by variations in production and processing. The tenderisation process was modelled on the activity of calpain proteinases. The extent of tenderisation is proportional to the level of calpains which accounts for the toughness of meat from β-adrenergic agonists. The rate of tenderisation increases with higher temperature and faster rigor development. These are responsible for the faster tenderisation in chicken, in meats following the use of electrical stimulation and in meats of high ultimate pH. Knowledge of these mechanisms of tenderisation afforded processes for optimisation of tenderness.

The concentrations of free magnesium and free calcium ions both increase in skeletal muscle fibres entering Rigor mortis

Metabolic inhibitors have been used to induce rigor in mammalian muscle fibres previously injected with the Ca(2+)- and Mg(2+)-binding dye arsenazo III. The spectral changes which ensue, after the onset of rigor, indicate that a large increase in intracellular free Ca(2+) occurs (to more than 10(-4)m) but that this is preceded and accompanied by a substantial increase in free Mg(2+) concentration (to 2 mm or more) presumably as a result of the decline in the ATP concentration within the cell. Fibres in rigor have been treated with the divalent cation ionophore A23187 to enable Ca(2+) and Mg(2+) to be extracted selectively from the cell by extracelluar chelating agents. Optical measurements performed during this extraction, confirm that both Ca(2+)- and Mg(2+)-binding to arsenazo III contribute to the absorption change which is recorded, whilst the treatment of relaxed fibres with the ionophore together with EDTA, produces an absorption change which, in combination with other measurements, indicates that in the sarcoplasm of the resting relaxed cell, approximately one third of the dye is complexed with Mg(2+). This indicates that the cytoplasmic free Mg(2+) concentration, prior to rigor onset, is about 0·5 mm.

Predation or scavenging? Thoracic muscle pH and rates of water loss reveal cause of death in arthropods

The difficulty of directly observing predatory events hinders a complete understanding of how predation structures food webs. Indirect approaches such as PCR-based and isotopic analyses clarify patterns of resource consumption but fail to distinguish predation from scavenging. Given that facultative scavenging is a ubiquitous and phylogenetically widespread foraging strategy, an improved ability to discriminate prey from carrion is needed to enhance an understanding of the demographic effects of consumption and the true nature of trophic interactions. Using physiological properties of muscle tissue – specifically pH and rate of water loss – we develop a novel method to discriminate prey from carrion collected by scavenging hymenopteran predators. Our focal system is the western yellowjacket (Vespula pensylvanica), a common scavenging predator in Hawaii and western North America. Prior to consumption, the physical properties of hymenopteran muscle tissue change in a quantifiable and deterministic manner post mortem and can be used to estimate the time and putative cause of death of diet items. Applying this method in laboratory and field situations resulted in the correct identification of prey and carrion in 49 out of 56 cases (88%). Although further investigation is needed to determine how post-mortem physiology of diet items changes in the guts of consumers, the approaches developed in this study can be used to distinguish predation from scavenging by central-place foragers (particularly arthropods). Such information will provide a more definitive characterization of species interactions and food webs.

Long persistence of rigor mortis at constant low temperature

We studied the persistence of rigor mortis by using physical manipulation. We tested the mobility of the knee on 146 corpses kept under refrigeration at Torino's city mortuary at a constant temperature of +4 degrees C. We found a persistence of complete rigor lasting for 10 days in all the cadavers we kept under observation; and in one case, rigor lasted for 16 days. Between the 11th and the 17th days, a progressively increasing number of corpses showed a change from complete into partial rigor (characterized by partial bending of the articulation). After the 17th day, all the remaining corpses showed partial rigor and in the two cadavers that were kept under observation "à outrance" we found the absolute resolution of rigor mortis occurred on the 28th day. Our results prove that it is possible to find a persistence of rigor mortis that is much longer than the expected when environmental conditions resemble average outdoor winter temperatures in temperate zones. Therefore, this datum must be considered when a corpse is found in those environmental conditions so that when estimating the time of death, we are not misled by the long persistence of rigor mortis.

Differential rigor development in red and white muscle revealed by simultaneous measurement of tension and stiffness

Based on the molecular mechanism of rigor mortis, we have proposed that stiffness (elastic modulus evaluated with tension response against minute length perturbations) can be a suitable index of post-mortem rigidity in skeletal muscle. To trace the developmental process of rigor mortis, we measured stiffness and tension in both red and white rat skeletal muscle kept in liquid paraffin at 37 and 25 degrees C. White muscle (in which type IIB fibres predominate) developed stiffness and tension significantly more slowly than red muscle, except for soleus red muscle at 25 degrees C, which showed disproportionately slow rigor development. In each of the examined muscles, stiffness and tension developed more slowly at 25 degrees C than at 37 degrees C. In each specimen, tension always reached its maximum level earlier than stiffness, and then decreased more rapidly and markedly than stiffness. These phenomena may account for the sequential progress of rigor mortis in human cadavers.

Method for determining if a corpse has been frozen: measuring the activity of short-chain 3-hydroxyacyl-CoA dehydrogenase (SCHAD)

Accidental deaths by exposure to the cold have figured in many publications, whereas the freezing of the corpse is not well known. The study which we have reported was motivated by an observation of homicide in which ignorance of the fact that the body had been frozen was responsible for an underestimation of the time since death. It proved that measuring the activity of short-chain 3-hydroxyacyl-CoA dehydrogenase (SCHAD) could reveal that the body had been frozen.

Development of rigor mortis is not affected by muscle volume

There is a hypothesis suggesting that rigor mortis progresses more rapidly in small muscles than in large muscles. We measured rigor mortis as tension determined isometrically in rat musculus erector spinae that had been cut into muscle bundles of various volumes. The muscle volume did not influence either the progress or the resolution of rigor mortis, which contradicts the hypothesis. Differences in pre-rigor load on the muscles influenced the onset and resolution of rigor mortis in a few pairs of samples, but did not influence the time taken for rigor mortis to reach its full extent after death. Moreover, the progress of rigor mortis in this muscle was biphasic; this may reflect the early rigor of red muscle fibres and the late rigor of white muscle fibres.

Reconsideration of the sequence of rigor mortis through postmortem changes in adenosine nucleotides and lactic acid in different rat muscles

We examined the changes in adenosine triphosphate (ATP), lactic acid, adenosine diphosphate (ADP) and adenosine monophosphate (AMP) in five different rat muscles after death. Rigor mortis has been thought to occur simultaneously in dead muscles and hence to start in small muscles sooner than in large muscles. In this study we found that the rate of decrease in ATP was significantly different in each muscle. The greatest drop in ATP was observed in the masseter muscle. These findings contradict the conventional theory of rigor mortis. Similarly, the rates of change in ADP and lactic acid, which are thought to be related to the consumption or production of ATP, were different in each muscle. However, the rate of change of AMP was the same in each muscle.

Estimating time of death from measurement of the electrical excitability of skeletal muscle

Post-mortem contraction was measured using sensitive force transducers inserted into human muscle. The muscle was stimulated using rectangular impulses of 1 sec duration and known current intensity. After some time, a noticeable change of the muscular contraction occurred, from a two-peak to a one-peak shape. The maximum force of the muscular contraction using a stable current intensity decreased with time since death, but relaxation time increased. The decrease of the maximum force and the increase of the relaxation time were used as criteria for extrapolating the time since death in a random sample of 50 bodies. The calculated 95% limits of confidence were 2.85 h (decrease of the maximum force) and 2.7 h (increase of relaxation time) up to 13 hours post mortem. The calculated 95% limits of confidence were checked on an independent sample of 21 bodies and proved to be reliable.

Effect of stresses before slaughter on changes to the physiological, biochemical and physical characteristics of duck muscle

1. This experiment was designed to study the effects of fasting and enforced exercise on the physiological, biochemical and physical characteristics of duck muscle. 2. Sixty 75-d-old male ducks weighing 3.0 +/- 0.2 kg were assigned to three treatments: a control, and an 8 and 24 h fast plus enforced exercise for 10 min. The ducks were then sacrificed and the carcass stored at 4 degrees C for 24 h. 3. Although the pH and serum lactate contents gradually increased with fasting time the responses were not significant. The ultimate pH was elevated and the lactate of breast and thigh muscles was lower in stressed birds. 4. The activity of lactic dehydrogenase was significantly increased by the stress, and the activities of creatine phosphokinase and alkaline phosphatase were also increased slightly. However, no effect was found on the ATPase activity of the myofibrillar protein of either breast or thigh muscle as a result of the stress. The ATPase activity of myofibrillar protein of breast muscle significantly increased with storage time. 5. The extractability of myofibrillar protein increased with storage time for all treatments. The SDS-PAGE patterns of myofibrillar proteins were also studied. 6. Consequently DFD-like muscle was observed in the breast and thigh muscles of ducks which had been stressed.