Environmental enrichment improves growth and fillet quality in rainbow trout

BACKGROUND

Some environmental enrichment methods, such as occupational enrichment (OE), can improve fish growth, but little is known about its effects on fillet quality. In this study, we evaluated the effects of OE using underwater currents on different aspects of fillet quality and muscle metabolism in rainbow trout (Oncorhynchus mykiss), before and after a handling procedure (fasting). The trout were placed in groups of 30 in separate tanks in three treatments for 30 days: no artificial currents (CON), randomly fired underwater currents (RFC), and continuous underwater currents (CUC). Additionally, half of the individuals in each treatment were fasted (5 days, 45.2 °C days).

RESULTS

Slaughter weight, condition factor, and relative growth were lower in CON fish, indicating a positive effect of OE on growth. Rigor mortis, muscle pH, and muscle glycogen levels were similar among treatments, indicating no effect of OE on classical measures of fillet quality. However, significant differences were found regarding fillet colour and muscle enzymes. The fillets of RFC fish were more salmon-pink in colour, which is favoured by consumers. Also, activity levels of pyruvate kinase and glycogen phosphorylase in muscle were significantly higher in CUC fish, probably due to increased energy demands, as pumps were on continually in that treatment.

CONCLUSION

Overall, RFC fish seemed to have received enough stimulation to improve growth while not being excessive in terms of exhausting the animals (avoiding negative effects on muscle metabolism), whereas OE may have provided a hormetic effect, allowing fish to better adjust to fasting. © 2023 Society of Chemical Industry.

Estimation of the post-mortem interval; added value of mechanical excitability of human skeletal muscle

Estimation of the post-mortem interval (PMI) is mainly based on the state of body cooling, post-mortem lividity (livor mortis) and post-mortem muscle stiffness (rigor mortis). However, the time span of development of these post-mortem phenomena are influenced by a variety of factors concerning the body of the deceased and the environment in which the body is found. Subsequently, this leads to a substantial spread in upper and lower limits of PMI based on determination of the state of these phenomena. Moreover, interpretation of post-mortem phenomena like lividity, rigor and interpretation of the correction factor for Henssge's nomogram is subjective. For this reason, PMI estimations are often broad, possibly too broad to be helpful for answering questions which are relevant for the criminal investigation. Therefore, combining the outcome of different methods for estimating the PMI, the so-called compound method, is recommended. Supravital muscle reaction by mechanical stimulation of skeletal muscle is a less known aspect of the compound method. Here we present a series of cases series in which supravital muscle reaction contributed to a more precise estimation of the PMI.

A comprehensive review of the spoilage of shrimp and advances in various indicators/sensors for shrimp spoilage monitoring

Shrimp is a popular internationally traded shellfish due to its unique taste, texture, and nutritional value. Shrimp is highly perishable because it has enough free amino acids, high moisture levels, non-nitrogenous compounds used for microbial growth, and melanosis. Shrimp spoilage after death is caused by various reasons, like autolysis (endogenous proteinases actions during shrimp storage), growth of spoilage microorganisms, ATP degradation, melanin formation, and lipid peroxidation. A microbial byproduct, total volatile basic nitrogen, is one of the major reasons for the generation of foul odors from shrimp spoilage. Shrimp freshness monitoring is crucial for market sellers and exporters. Traditional methods for estimating shrimp freshness are expensive and inaccessible to the general public. Sensors are rapid, sensitive, selective, and portable food toxins' detection tools, devoid of expensive instruments, skilled people, sample pretreatment, and a long detection time. This review addresses shrimp spoilage causes. The mechanisms of different stages of shrimp spoilage after death, like rigor mortis, dissolution of rigor mortis, autolysis, and microbial spoilage mechanisms, are discussed. This review highlights the last five years' advances in shrimp freshness detection sensors and indicators like colorimetric pH indicators, fluorescence sensors, electronic noses, and biosensors, their working principles, and their sensitivities. Commercially available indicators and sensors for shrimp spoilage monitoring are also discussed. A review highlighting the applications of the different sensors and indicators for monitoring shrimp freshness is unavailable to date. Challenges and future perspectives in this field are explained at the end.

Technical note: Validity of a non-destructive device for opening dental arches in rigor mortis cadavers

Forensic dental autopsy is a fundamental procedure for the study of a death under judicial investigation in the search for postmortem (PM) information that can be compared with the antemortem (AM) data available from the cadaver. One of the major difficulties in taking postmortem evidence is the opening of the mouth, limited in many cases by the phenomenon of cadaveric rigidity or rigor mortis. The aim of this study was to evaluate the effectiveness of a new device designed to facilitate the opening of the dental arches in rigor mortis corpses. For this purpose, a sample of 30 corpses (22 men and 8 women; mean age 42.18 years and 38.75 years) from the Institute of Legal Medicine of the city of Lima (Peru) was analyzed. A forensic odontologist designed and manufactured the apparatus and carried out the sample analysis process. The initial and maximum measurements of oral cavity opening were recorded and a paired Student's t-test was applied to observe the difference between these initial and maximum measurements obtained (p < 0.05). The results showed that the average oral opening obtained with the new appliance was 43.83 ± 3.62 mm, with an average initial opening of 6.49 ± 3.04 mm (p < 0.001). The efficacy was similar in men and women (maximum opening M: 51.70 mm - F: 53.00 mm). In 29 of the 30 carcasses studied (96.7%) an opening greater than 40 mm was obtained, the latter being a minimum measurement sufficient to access the oral cavity. The efficacy of this new instrument for oral autopsy purposes is highlighted, since it does not cause destruction of the soft tissues and allows the correct manipulation of the oral structures present.

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.

Effects of super-chilling storage on shelf-life and quality indicators of Coregonus peled based on proteomics analysis

The advantages of super-chilling storage at -2 °C for maintaining the quality of Coregonus peled muscle were investigated using the rigor-mortis index (RM), ATP-related compounds, K-value, muscle hardness, impedance measurement, and total viable count. The results indicated that the softening of fish muscle and increase in K-value were substantially suppressed following storage at -2 °C compared to that at 0 °C. In particular, the hardness of fish muscle stored for 6 days at -2 °C was much higher than that of the samples stored for 2 days at 0 °C. The K-value increased to 81% after 6 days at 0 °C, while increased to 57% at -2 °C. The impedance changed in a biphasic manner throughout the storage period. The initial increase accompanied by the progression of RM was followed by a gradual decrease. However, this decrease was much slower at -2 °C than 0 °C. Furthermore, proteomics analysis demonstrated that the mechanism of fish freshness changes between the two storage temperatures. Differentially abundant proteins between the samples stored at two temperatures were mainly involved in the cellular component and molecular function (GO pathway) as well as collagen digestion (KEGG pathway), which might be related to muscle textural properties. Therefore, super-chilling storage is a possible method for maintaining the freshness of Coregonus peled.

Resting time before slaughter restores homeostasis, increases rigor mortis time and fillet quality of surubim Pseudoplatystoma spp

This study assesses the respiratory dynamics related to stress parameters and resting time before slaughter, in the quality of surubim (Pseudopatystoma spp.) fillets. A completely randomized design was conducted using five treatments: resting time before slaughter of 0, 2, 4, 8 and 24 hours, with 15 fish sampled per treatment. Time 0 corresponded to the treatment without resting time, where the fish were slaughtered immediately after arriving at the processing plant. The resting time did not affect the electrolyte balance, hemoglobin, plasma, hepatic glycogen, myofibrillar fragmentation index (MFI) and water holding capacity (WHC) of surubins. However, with increased resting time, there was a significant decrease in muscle glycogen and an increase in blood pH and blood bicarbonate levels. Additionally, respiratory parameters showed an increase in pO₂ and, consequently, in O₂ saturation and a decrease in pCO₂.The hematocrit and MCV values of the surubins after 24 hours of resting decreased significantly. In the first hours of resting, the highest values of erythrocytes and CHCM were observed. The lowest level of stress was observed for fish having 24 hours of resting. Fish having longer resting periods (8 and 24 hours) presented fillets with a higher pH (P <0.05) and the rigor mortis establishment time was shorter for the first 2 hours and 24 hours of resting time. There was a linear decrease in fillet lightness and an increase in the intensity of red (CIE a*) color up to 24 hours when resting was increased. In CIE b*, a linear decrease (P <0.05) of the yellow intensity of the fillets was observed as the surubim resting time increased. A resting time of 4 to 8 hours before slaughter is effective in reestablishing homeostasis after transporting surubim, providing fillets with higher quality and a greater length of the pre-rigor mortis period.

Effects of three different stunning/slaughtering methods on physical, chemical, and sensory changes in rainbow trout (Oncorhynchus mykiss)

BACKGROUND

Electrical stunning (E) and asphyxia in the air (A) are two common stunning/killing methods for fish. However, they can stress the fish and affect flesh quality, so an alternative should be found. The present study aimed to evaluate the effects of carbon monoxide asphyxia (CO) compared to E and A on the evolution of post rigor mortis changes in rainbow trout (Oncorhynchus mykiss) fillets related to chemical, textural, and sensorial properties during storage time.

RESULTS

Fish fillets from the E group showed a higher pH (P < 0.05) than the A ones, both at time of rigor resolution (T_RR 0) and from T_RR 4 until T_RR 7 (7 days after rigor resolution, which corresponded to 10 days post mortem), with the CO group being always intermediate. The CO treatment ensured that the fillets showed the lowest yellowness index (b*), even if only at T_RR 2 and T_RR 5. Lipid oxidation and texture profile analyses were unaffected. Sensory analysis revealed that the CO fillets had the lowest odor intensity and the highest juiciness scores (P < 0.05). The sensory descriptors resulted the most discriminant variables of the fillets obtained from the differently stunned animals, as resulted by the canonical discriminant analysis.

CONCLUSION

The carbon monoxide stunning/slaughtering method could be applied to rainbow trout without detrimental effects on physical, chemical, or sensory characteristics of the fish flesh. © 2018 Society of Chemical Industry.

Carbon monoxide stunning of Atlantic salmon (Salmo salar L.) modifies rigor mortis and sensory traits as revealed by NIRS and other instruments

BACKGROUND

Methods of stunning used in salmon slaughter are still the subject of research. Fish quality can be influenced by pre-, ante- and post-mortem conditions, including handling before slaughter, slaughter methods and storage conditions. Carbon monoxide (CO) is known to improve colour stability in red muscle and to reduce microbial growth and lipid oxidation in live fish exposed to CO. Quality differences in Atlantic salmon, Salmo salar L., stunned by CO or percussion, were evaluated and compared by different techniques [near infrared reflectance spectroscopy (NIRS), electronic nose (EN), electronic tongue (ET)] and sensory analysis.

RESULTS

Thawed samples, freeze-dried preparates and NIRS devices proved to be the most efficient combinations for discriminating the treatments applied to salmon, i.e. first the stunning methods adopted, then the back-prediction of the maximum time to reach rigor mortis and finally to correlate some sensory attributes. A trained panel found significant differences between control and CO-stunned salmon: reduced tactile crumbliness, reduced odour and aroma intensities, and reduced tenderness of CO-treated fillets. CO stunning reduced radiation absorbance in spectra of thawed and freeze-dried fillets, but not fillet samples stored in ethanol, where it may have interacted with myoglobin and myosin.

CONCLUSIONS

The good results in a rapid discrimination of thawed samples detected by NIRS suggest suitable applications in the fish industry. CO treatment could mitigate sensory perception, but consumer tests are needed to confirm our findings. © 2015 Society of Chemical Industry.

Rigor Mortis: Statistical thoroughness in reporting and the making of truth

Should a uniform checklist be adopted for methodological and statistical reporting? The current article discusses this notion, with particular attention to the use of old versus new statistics, and a consideration of the arguments brought up by Von Roten. The article argues that an overly exhaustive checklist that is uniformly applied to all submitted papers may be unsuitable for multidisciplinary work, and would further result in undue clutter and potentially distract reviewers from pertinent considerations in their evaluation of research articles.

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.

Quantitative phosphoproteomic analysis of porcine muscle within 24 h postmortem

Protein phosphorylation can regulate most of the important processes in muscle, such as metabolism and contraction. The postmortem (PM) metabolism and rigor mortis have essential effects on meat quality. In order to identify and characterize the protein phosphorylation events involved in meat quality development, a quantitative mass spectrometry-based phosphoproteomic study was performed to analyze the porcine muscle within 24h PM using dimethyl labeling combined with the TiSH phosphopeptide enrichment strategy. In total 305 unique proteins were identified, including 160 phosphoproteins with 784 phosphorylation sites. Among these, 184 phosphorylation sites on 93 proteins had their phosphorylation levels significantly changed. The proteins involved in glucose metabolism and muscle contraction were the two largest clusters of phosphoproteins with significantly changed phosphorylation levels in muscle within 24 h PM. The high phosphorylation level of heat shock proteins (HSPs) in early PM may be an adaptive response to slaughter stress and protect muscle cell from apoptosis, as observed in the serine 84 of HSP27. This work indicated that PM muscle proteins underwent significant changes at the phosphorylation level but were relatively stable at the total protein level, suggesting that protein phosphorylation may have important roles in meat quality development through the regulation of proteins involved in glucose metabolism and muscle contraction, thereby affecting glycolysis and rigor mortis development in PM muscle.

BIOLOGICAL SIGNIFICANCE

The manuscript describes the characterization of postmortem (PM) porcine muscle within 24 h postmortem from the perspective of protein phosphorylation using advanced phosphoproteomic techniques. In the study, the authors employed the dimethyl labeling combined with the TiSH phosphopeptide enrichment and LC-MS/MS strategy. This was the first high-throughput quantitative phosphoproteomic study in PM muscle of farm animals. In the work, both the proteome and phosphoproteome were analyzed, and the large number of identified peptides, phosphopeptides and phosphorylation sites can greatly enrich the current farm animal protein database. The proteins involved in glycometabolism, muscle contraction and heat shock proteins (HSPs) showed significantly changed phosphorylation levels during PM meat development. This work indicated that PM muscle proteins underwent significant changes at phosphorylation level but were relatively stable at the total protein level, suggesting that protein phosphorylation may have important roles in meat development through the regulation of proteins involved in metabolism and muscle contraction, thereby affecting glycolysis and rigor mortis development in PM muscle. The work can promote the understanding of PM muscle metabolism and meat quality development, and be helpful for future meat quality control.

Care of relatives following sudden infant death

This paper deals with 301 families who have been offered a consultation for managing bereavement following sudden infant death. Eighty-eight percent of the parents (269 families) accepted and 36 more families out with Lower Saxony wished to be cared for. Without a previous autopsy 1.172 contacts happened from 1989 to 2003 comprising primary crisis intervention and long-term care, the latter including saying farewell before and after autopsy. One main aim was a close linking with the international self-help organization of parents (GEPS). Single cases conferences were carried out for more than five years according to the Sheffield model. There is given the methodical basis and many details of the care project.

Accelerated recovery of Atlantic salmon (Salmo salar) from effects of crowding by swimming

The effects of post-crowding swimming velocity (0, 0.35, and 0.70 m/s) and recovery time (1.5, 6, and 12 h) on physiological recovery and processing quality parameters of adult Atlantic salmon (Salmo salar) were determined. Atlantic salmon crowded to a density similar to that of a commercial slaughter process (>200 kg/m(3), 40 min) were transferred to a swimming chamber for recovery treatment. Osmolality and concentrations of cortisol, glucose and lactate in blood plasma were used as physiological stress indicators, whereas image analyses of extent and duration of rigor contraction, and fillet gaping were used as measures of processing quality. Crowded salmon had a 5.8-fold higher plasma cortisol concentration than control salmon (P<0.05). The elevated plasma cortisol concentration was reduced by increasing the swimming velocity, and had returned to control levels after 6 h recovery at high water velocity. Similar effects of swimming velocity were observed for plasma osmolality and lactate concentration. A lower plasma glucose concentration was present in crowded than in control fish (P<0.05), although a typical post-stress elevation in plasma glucose was observed after the recovery treatments. Lower muscle pH was found in crowded compared with control salmon (P<0.05), but muscle pH returned to control levels after 6 h recovery at intermediate and high swimming velocities and after 12 h in the low velocity group. Crowding caused an early onset of rigor mortis contraction. However, subjecting crowded salmon to active swimming for 6 h before slaughter delayed the onset of rigor mortis contraction from 2.5 to 7.5 h post mortem. The extent of rigor mortis contraction was also affected by crowding and post-stress swimming activity (P<0.05), and the largest degree of contraction was found in crowded salmon. In conclusion, active swimming accelerated the return of plasma cortisol, hydromineral balance, and the energy metabolism of adult Atlantic salmon to pre-stress levels. Moreover, an active swimming period delayed the onset of rigor mortis contraction, which has a positive technological implication for the salmon processing industry.

Rigor development and meat quality of large and small broilers and the use of Allo-Kramer shear, needle puncture, and razor blade shear to measure texture

In each of 2 trials, 75 female and 75 male broilers of different sizes (large and small) were obtained from a commercial grower and were commercially processed. Breast fillets were deboned at 0.25, 1.5, 3, 6, and 24 h postmortem (total n = 15 per treatment per time point). Muscle pH and L* value were determined for each deboning time. Breast fillets were subjected to texture analysis using Allo-Kramer (10-blade), needle puncture (2 mm diameter), or razor blade shear (8.9 mm wide) methods. Allo-Kramer tests were performed on a strip (40 x 20 x 7 mm); needle puncture and razor blade shear were performed on intact muscles. Body size and sex had no effect on rigor development or color as indicated by no significant difference in breast muscle pH, R-value, or L* value. Allo-Kramer and razor blade tests exhibited significant shear value differences among samples deboned early (<1.5 h) and late (>6 h) PM. Allo-Kramer shear and razor blade tests performed similarly for differentiating breast meat of different toughness though Allo-Kramer shear force and razor blade energy were only moderately correlated (r = 0.72). Although both instrumental tests were performed in the same approximate area on each breast, it is possible that variation within the breast would have caused this marginal correlation. Although further studies would be necessary to compare the performance of both tests for assessing poultry meat toughness, the proposed razor blade test has the advantage of requiring no sample preparation (i.e., cutting a strip of constant dimensions) other than cooking.

Improving laparoscopy in embalmed cadavers: a new method with a lateral abdominal wall muscle section

BACKGROUND

Rigor mortis can be a problem when laparoscopy is performed in embalmed cadavers for surgical training.

METHODS

To improve the laparoscopic view, a new technique for managing the abdominal wall with a cutaneous-subcutaneous flap, pneumoperitoneum (14-15 mmHg), and a progressive (step-by-step) bilateral section of the lateral muscles of the abdomen was attempted in 10 embalmed cadavers. The degree of abdominal wall increase was calculated by measuring changes in the size of the abdominal wall after each step. Improvement in the peritoneal laparoscopic view was also assessed.

RESULTS

For abdominal wall size, no constant relationship was observed between initial (after creation of the pneumoperitoneum) and final increment (after each muscular layer section). Cumulative degrees of increase in the dimensions of the abdominal wall were the only parameters that showed a significant difference among the four groups of cadavers. Bilateral sectioning of both oblique muscles was sufficient to obtain an adequate view of the abdominopelvic cavity; thus, the risk of an unexpected peritoneal opening during sectioning of the transversum abdominis muscle was obviated.

CONCLUSIONS

In embalmed cadavers, the laparoscopic view in the presence of a pneumoperitoneum can be facilitated by a section of the lateral muscles of the abdomen, with a previous cutaneous-subcutaneous flap. To obviate an incidental opening of the peritoneum, resulting in air leakage, preservation of the deep muscular layer is advisable.

Forensic entomology

Necrophagous insects are important in the decomposition of cadavers. The close association between insects and corpses and the use of insects in medicocriminal investigations is the subject of forensic entomology. The present paper reviews the historical background of this discipline, important postmortem processes, and discusses the scientific basis underlying attempts to determine the time interval since death. Using medical techniques, such as the measurement of body temperature or analysing livor and rigor mortis, time since death can only be accurately measured for the first two or three days after death. In contrast, by calculating the age of immature insect stages feeding on a corpse and analysing the necrophagous species present, postmortem intervals from the first day to several weeks can be estimated. These entomological methods may be hampered by difficulties associated with species identification, but modern DNA techniques are contributing to the rapid and authoritative identification of necrophagous insects. Other uses of entomological data include the toxicological examination of necrophagous larvae from a corpse to identify and estimate drugs and toxicants ingested by the person when alive and the proof of possible postmortem manipulations. Forensic entomology may even help in investigations dealing with people who are alive but in need of care, by revealing information about cases of neglect.

Evaluation of physical dimension changes as nondestructive measurements for monitoring rigor mortis development in broiler muscles

Studies were conducted to develop a non-destructive method for monitoring the rate of rigor mortis development in poultry and to evaluate the effectiveness of electrical stimulation (ES). In the first study, 36 male broilers in each of two trials were processed at 7 wk of age. After being bled, half of the birds received electrical stimulation (400 to 450 V, 400 to 450 mA, for seven pulses of 2 s on and 1 s off), and the other half were designated as controls. At 0.25 and 1.5 h postmortem (PM), carcasses were evaluated for the angles of the shoulder, elbow, and wing tip and the distance between the elbows. Breast fillets were harvested at 1.5 h PM (after chilling) from all carcasses. Fillet samples were excised and frozen for later measurement of pH and R-value, and the remainder of each fillet was held on ice until 24 h postmortem. Shear value and pH means were significantly lower, but R-value means were higher (P < 0.05) for the ES fillets compared to the controls, suggesting acceleration of rigor mortis by ES. The physical dimensions of the shoulder and elbow changed (P < 0.05) during rigor mortis development and with ES. These results indicate that physical measurements of the wings maybe useful as a nondestructive indicator of rigor development and for monitoring the effectiveness of ES. In the second study, 60 male broilers in each of two trials were processed at 7 wk of age. At 0.25, 1.5, 3.0, and 6.0 h PM, carcasses were evaluated for the distance between the elbows. At each time point, breast fillets were harvested from each carcass. Fillet samples were excised and frozen for later measurement of pH and sacromere length, whereas the remainder of each fillet was held on ice until 24 h PM. Shear value and pH means (P < 0.05) decreased, whereas sarcomere length means (P < 0.05) increased over time, indicating rigor mortis development. Elbow distance decreased (P < 0.05) with rigor development and was correlated (P < 0.01) with shear value (r = 0.2581), sarcomere length (r = -0.3079), and pH (r = 0.6303). These results suggest that elbow distance could be used in conjunction with other detection methods for optically automating measurement of rigor mortis development in broiler carcasses.

Double freezing of cod fillets: influence on sensory, physical and chemical attributes of battered and breaded fillet portions

Fillet samples were processed on board a research vessel from cod (Gadus morhua) in different states of rigor mortis. In addition, headed and gutted fish in different states of rigor were frozen and, after ten days of frozen storage, the fish were thawed, processed into fillets and refrozen. During subsequent frozen storage at -24 degrees C of breaded and battered portions processed from the different fillet batches several quality attributes were tested using sensory, physical, and chemical methods. The measurements indicated differences in the quality attributes depending on refreezing and rigor states. Especially the sensory texture attributes gumminess and, with some restrictions, firmness were found to be suitable for distinguishing single frozen (SF) from double frozen (DF) samples. This finding was supported by the outcome of the measurement of penetration force where generally a significantly (p < 0.05) higher force was necessary to penetrate the DF compared to SF samples. DF samples were generally lighter (higher L*) than SF samples. The colour difference delta E between both sample types was at least very clear and therefore visible. However, no clear differences between SF and DF samples were found when evaluating the flavour attributes and using instrumental texture profile analysis for texture characterisation. Also, all chemical parameters measured did not allow to clearly distinguish between single and double frozen samples. Therefore, it can be stated that, at least when using cod as raw material for processing battered and breaded portions, the different methods for preparing the fillet blocks will, if at all, only affect the textural quality of the final products.

Effects of feed deprivation and electrical, gas, and captive needle stunning on early postmortem muscle metabolism and subsequent meat quality

The general method for stunning poultry before slaughter is by immersion of a chicken's head into an electrified waterbath. This method results in carcass and meat quality deficiencies. The major problems are hemorrhages and a delay in onset of rigor mortis, which increases the risk of cold shortening with early deboning. In two experiments, this study examines the early postmortem metabolism in the breast muscle and its effect on ultimate meat quality. The first experiment describes the effects of 5 h feed deprivation on the availability of glycogen from the liver and the breast muscle, of waterbath and head-only electrical stunning on pH and metabolite levels up to 6 h in unprocessed muscle, and the consequences on meat quality. The second experiment compares the same measurements after waterbath and head-only electrical stunning, CO2/O2/N2 and Ar/CO2 gases, and captive needle stunning. Metabolic degradation halted after 6 h without processing or after 4 h under conventional conditions after waterbath and CO2/O2/N2 stunning. With other stunning methods, this occurrence is at a faster rate, largely depending on muscle activity. Muscle glycogen does not need to be exhausted for energy generation to cease. If glycogen is a limiting factor, as found with head-only stunning, pH drops too rapidly and affects water-holding capacity and color. Hemorrhage scores were higher with electrical stunning than with other stunning methods. Gas stunning affected color and, to a lesser extent, water-holding capacity. Captive needle stunning scored between gas and electrical stunning on most measurements.

Double freezing of saithe fillets. Influence on sensory and physical attributes

Fillet samples were processed on board of a research vessel from saithe (Pollachius virens) in different states of rigor mortis. In addition, headed and gutted fish in different states of rigor were frozen and, after ten days of frozen storage, the fish were thawed, processed into fillets and refrozen. During subsequent frozen storage at -24 degrees C several quality attributes were tested using sensory (Quantitative Descriptive Analysis schemes for flavour and texture) and physical (Texture Profile Analysis, penetration force, colour measurement) methods. The measurements indicated differences in the quality attributes depending on refreezing and rigor states. However, it was not possible to clearly distinguish between single and double frozen samples. Therefore, it can be stated that, at least when using saithe as raw material for processing battered and breaded portions, the different methods of preparing the fillet blocks will not significantly affect the quality of the final products.

Forced oral opening for cadavers with rigor mortis: two approaches for the myotomy on the temporal muscles

Forensic dentistry plays an essential role in personal identification procedures. An adequate interincisal space of cadavers with rigor mortis is required to obtain detailed dental findings. We have developed intraoral and two directional approaches, for myotomy of the temporal muscles. The intraoral approach, in which the temporalis was dissected with scissors inserted via an intraoral incision, was adopted for elderly cadavers, females and emaciated or exhausted bodies, and had a merit of no incision on the face. The two directional approach, in which myotomy was performed with thread-wire saw from behind and with scissors via the intraoral incision, was designed for male muscular youths. Both approaches were effective to obtain a desired degree of an interincisal opening without facial damage.

Experiences with a compound method for estimating the time since death. II. Integration of non-temperature-based methods

The period since death was estimated at the scene in 72 consecutive cases using the temperature-based nomogram method as the primary method and supplemented by examination of criteria such as lividity, rigor mortis, mechanical and electrical excitability of skeletal muscle and chemical excitability of the iris. A case-oriented, computer-assisted selection of the non-temperature-based methods and integration of the results into a common result of the compound method was made following a special logistic. The limits of the period since death as estimated by the nomogram were improved in 49 cases by including the non-temperature-based methods and also provided results in 4 cases where the temperature method could not be used. In a further 6 cases the non-temperature-based methods confirmed the limits estimated by the temperature method but in 14 cases a useful result could not be obtained. In only one of the cases investigated was the upper limit of the period since death, as estimated by the criterion re-establishment of rigor (8 h post-mortem), in contradiction with the period determined by the police investigations (9.4 h post-mortem).

Onset of rigor mortis is earlier in red muscle than in white muscle

Rigor mortis is thought to be related to falling ATP levels in muscles postmortem. We measured rigor mortis as tension determined isometrically in three rat leg muscles in liquid paraffin kept at 37 degrees C or 25 degrees C--two red muscles, red gastrocnemius (RG) and soleus (SO) and one white muscle, white gastrocnemius (WG). Onset, half and full rigor mortis occurred earlier in RG and SO than in WG both at 37 degrees C and at 25 degrees C even though RG and WG were portions of the same muscle. This suggests that rigor mortis directly reflects the postmortem intramuscular ATP level, which decreases more rapidly in red muscle than in white muscle after death. Rigor mortis was more retarded at 25 degrees C than at 37 degrees C in each type of muscle.

Rigor mortis development in turkey breast muscle and the effect of electrical stunning

Rigor mortis development in turkey breast muscle and the effect of electrical stunning on this process are not well characterized. Some electrical stunning procedures have been known to inhibit postmortem (PM) biochemical reactions, thereby delaying the onset of rigor mortis in broilers. Therefore, this study was designed to characterize rigor mortis development in stunned and unstunned turkeys. A total of 154 turkey toms in two trials were conventionally processed at 20 to 22 wk of age. Turkeys were either stunned with a pulsed direct current (500 Hz, 50% duty cycle) at 35 mA (40 V) in a saline bath for 12 seconds or left unstunned as controls. At 15 min and 1, 2, 4, 8, 12, and 24 h PM, pectoralis samples were collected to determine pH, R-value, L* value, sarcomere length, and shear value. In Trial 1, the samples obtained for pH, R-value, and sarcomere length were divided into surface and interior samples. There were no significant differences between the surface and interior samples among any parameters measured. Muscle pH significantly decreased over time in stunned and unstunned birds through 2 h PM. The R-values increased to 8 h PM in unstunned birds and 24 h PM in stunned birds. The L* values increased over time, with no significant differences after 1 h PM for the controls and 2 h PM for the stunned birds. Sarcomere length increased through 2 h PM in the controls and 12 h PM in the stunned fillets. Cooked meat shear values decreased through the 1 h PM deboning time in the control fillets and 2 h PM in the stunned fillets. These results suggest that stunning delayed the development of rigor mortis through 2 h PM, but had no significant effect on the measured parameters at later time points, and that deboning turkey breasts at 2 h PM or later will not significantly impair meat tenderness.

The influence of postmortem electrical stimulation on rigor mortis development, calpastatin activity, and tenderness in broiler and duck pectoralis

This study was conducted to evaluate the effects of electrical stimulation (ES) on rigor mortis development, calpastatin activity, and tenderness in anatomically similar avian muscles composed primarily of either red or white muscle fibers. A total of 72 broilers and 72 White Pekin ducks were either treated with postmortem (PM) ES (450 mA) at the neck in a 1% NaCl solution for 2 s on and 1 s off for a total of 15 s or were used as nonstimulated controls. Both pectoralis muscles were harvested from the carcasses after 0.25, 1.25, and 24 h PM and analyzed for pH, inosine:adenosine ratio (R-value), sarcomere length, gravimetric fragmentation index, calpastatin activity, shear value, and cook loss. All data were analyzed within species for the effects of ES. Electrically stimulated ducks had a lower muscle pH at 0.25 and 1.25 h PM and higher R-values at 0.25 h PM compared with controls. Electrically stimulated broilers had a lower muscle pH at 1.25 h and higher R-values at 0.25 and 1.25 h PM compared with controls. Muscles of electrically stimulated broilers exhibited increased myofibrillar fragmentation at 0.25 and 1.25 h PM, whereas there was no such difference over PM time in the duck muscle. Electrical stimulation did not affect calpastatin activity in either broilers or ducks; however, the calpastatin activity of the broilers did decrease over the aging time period, whereas that of the ducks did not. Electrical stimulation decreased shear values in broilers at 1.25 h PM compared with controls; however, there was no difference in shear values of duck muscle due to ES at any sampling time. Cook loss was lower for electrically stimulated broilers at 0.25 and 1.25 h PM compared with the controls, but had no effect in the ducks. These results suggest that the red fibers of the duck pectoralis have less potential for rigor mortis acceleration and tenderization due to ES than do the white fibers of the broiler pectoralis.

The development of pale, exudative meat in two genetic lines of turkeys subjected to heat stress and its prediction by halothane screening

Previous research has indicated that seasonal-type heat stress (HS) can contribute to the development of pale, soft, exudative (PSE) meat in fast-growing turkeys and that halothane exposure may identify stress-susceptible animals. This study evaluated the ability of halothane screening to identify stress-susceptible birds prone to developing pale, exudative meat when reared to market age. Two lines of turkeys (n = 292), one selected for rapid overall growth (BODY) and the other for large breast muscle yield (BREAST), were exposed to 3% halothane for 5 min at 2 to 4 wk of age and were raised together until 16 wk of age. Approximately 10% of both BODY and BREAST birds were sensitive to halothane. Between 16 and 20 wk, all of the halothane sensitive (HAL+) and half of the halothane nonresponders (HAL-) were exposed to an HS environment of 30 to 36 C (night/day), whereas the other half of the HAL- birds were kept at an ambient temperature of 13 to 21 C (night/day). All birds were slaughtered at 20 wk of age, and samples were collected for pH, L* value, drip loss, cooking loss, and shear value. The BREAST strain had 5% greater breast percentage than the BODY strain, and there were no differences in ready-to-cook yields between any treatments. The HAL+ HS birds had significantly lower muscle pH (0 h) and significantly higher L* values at 2 h postmortem compared with HAL- HS birds in the BREAST strain; however, there was no difference in L* value at 24 h postmortem. The HAL- HS birds had significantly lower muscle pH (0 h and 2 h) and significantly higher L* values at 2 h postmortem compared with HAL- controls in the BODY strain. The HAL- HS BREAST birds had significantly higher drip loss than HAL- controls. No differences in shear value were found among any treatments. The incidence of PSE (2-h L* values >52) was significantly higher in HAL+ HS birds (34.7%) compared with HAL- HS birds (13.4%). These results suggest that halothane sensitivity early in life is associated with HS susceptibility and the development of pale meat when birds are slaughtered at market age. These results also suggest that halothane screening may be better at predicting the development of PSE meat during HS in the strain selected for large breast yield rather than rapid overall growth.

A halothane test to detect turkeys prone to developing pale, soft, and exudative meat

The turkey industry suffers from pale, soft, and exudative meat (PSE) that is unsuitable for further processing because of excessive color variation, poor meat binding, and depressed water holding ability. This condition is caused by accelerated postmortem muscle metabolism and is thought to be related to a similarly inherited condition in swine. A quick, nondestructive method of screening animals is needed to avoid further propagation of PSE in breeding flocks. In this study, a halothane test used with swine was evaluated as a possible detection method for PSE-susceptible turkeys. In Experiment 1, a commercial strain of 4-wk-old male turkeys (n = 116) was exposed to 3% halothane gas for 3 min (6 L/min) and examined for leg muscle rigidity. Experiment 2 followed similar testing measures, using two strains of growth-selected turkeys (n = 504). Measurements of pH, R-value (ratio of inosine:adenosine), color, and expressible moisture content were made from each bird's breast fillet to determine whether the muscles of the responding birds would develop PSE characteristics. Five percent of tested birds in the first experiment and 2% in the second experiment exhibited rigid legs, indicating some of the discriminating power of this test. However, the data indicated that the characteristics of muscles from these birds did not differ from those of the nonresponding birds (P < 0.05). Possibly, the birds may need to be screened or slaughtered at a different age or using different methods.

Relationship between muscle growth and poultry meat quality

For a number of years, poultry selection has concentrated on growth velocity in meat lines, producing improvements in growth that have not been without consequence for muscle structure, metabolism, and meat quality. Higher growth rates may induce morphological abnormalities, induce larger fiber diameters and a higher proportion of glycolytic fibers, and a lower proteolytic potential in the muscles. After death, the faster development of rigor mortis increases the likelihood of paler color and reduced water holding capacity and poorer quality of further processed products. Reduced proteolytic potential is likely to increase toughness of poultry meats.

The effects of antemortem electrical stunning and postmortem electrical stimulation on biochemical and textural properties of broiler breast meat

Experiments were conducted to determine the combined effects of antemortem electrical stunning (STUN) and postmortem electrical stimulation (STIM) on breast muscle rigor development and meat quality attributes. Birds were either unstunned, stunned with low voltage (LV), or stunned with high current (HC) prior to conventional killing. Immediately after exsanguination, birds were either unstimulated, or were subjected to electrical stimulation with 12 1s on/1s off pulses of 440 V AC and allowed to bleed for 90 s to determine the effect of treatment on blood loss. Breast fillets (Pectoralis major) were removed from carcasses immediately after evisceration (0.25 h) or after aging in a static ice-water slush for 1 or 2 h, and analyzed for muscle pH, R-value (ratio of inosine to adenosine nucleotides), and sarcomere length. Raw breast meat color (CIELAB), cook loss, and shear values were determined on samples held at 2 C for 24 h. Results showed both STUN and STIM significantly affected blood loss, pH, R-value, sarcomere length, color, and shear, and there were significant STUN by STIM interactions. Blood loss was significantly lower for the HC STUN and all the STIM treatments. STIM at 440 V resulted in accelerated rigor development as measured by pH, R-value, and sarcomere length, similar to the unstunned or LV STUN samples, but different from the HC STUN birds. These results indicate that electrical stimulation may accelerate rigor most effectively following high current stunning, which tends to delay early rigor development.

Tenderness of broiler breast fillets from carcasses treated with electrical stimulation and extended chilling times

Postmortem electrical stimulation (ES) (450 V, 450 mA, 2 s on, 1 s off for five pulses) has been shown to decrease the toughness associated with early deboning. Most studies involving this system have been concerned with obtaining "acceptable" tenderness in fillets deboned at about 1 h postmortem, the time of carcass exit from an immersion chiller. However, the effects of ES combined with deboning at 2 h postmortem needs to be evaluated because some processors are considering extended immersion chilling and those already using air chilling require approximately 2 h for this process. Two 32-bird trials were conducted to compare tenderness in broiler breast fillets from ES-treated carcasses deboned at 1 and 2 h postmortem and fillets from control (C) carcasses deboned at 1 and 4 h postmortem. The Allo-Kramer shear value means of ES-2 h and C-4 h fillets were not different from each other and were significantly lower than that of the ES-lh fillets, which was significantly lower than the C-lh fillets. There was no significant difference among treatments associated with thaw loss or cook loss. The ES-2 h, ES-1 h, and C-4 h samples had significantly higher R-values and lower pH values than the C-1 h samples, indicating more advanced rigor development. These results indicate that deboning fillets from ES-treated carcasses at 2 h postmortem yields meat with a tenderness equivalent to the value reached with 4 h aging on the carcass. This is a 50% reduction in the time needed to achieve this level of tenderness.

Bleedout efficiency, carcass damage, and rigor mortis development following electrical stunning or carbon dioxide stunning on a shackle line

In Experiment 1, 400 male broilers were stunned using a gradient of 40 to 60% CO2 over a period of 25 s or a 1% brine solution that was electrically charged (35 mA) for 7 s. Blood loss during bleeding was measured in 30-s intervals for a total of 120 s. After conventional processing and chilling, carcass damage was subjectively evaluated. Results indicated that the birds stunned with electricity bled faster than the CO2-stunned birds until 60 s. However, the cumulative blood loss was not different after 90 s. Carcass damage evaluation indicated that birds stunned with CO2 had a significantly lower percentage of broken clavicles, and had fewer hemorrhages on the surface of the Pectoralis. However, there was no difference between the two stunning methods in the frequency of damage at the shoulder. In Experiment 2, 256 broilers were stunned using the same conditions as in Experiment 1. Measurements of pH, R-value, sarcomere length (SL), and fragmentation index (FI) were evaluated from the left breast fillets harvested at 0, 1, 2, and 6 h postmortem. Shear values (SV) were determined using the right fillets harvested at the same four postmortem times and aged on ice until 24 h. No significant difference in breast muscle pH value was observed at 0, 2, and 6 h postmortem. However, CO2-stunned fillets had significantly higher pH values than the ES fillets at 1 h postmortem. Carbon dioxide produced greater R values than electricity at 2 and 6 h. Sarcomere length, FI, and SV were not significantly different at any time tested. These data suggest that CO2 stunning reduced carcass damage but did not reduce the need for aging before deboning when compared to the electrical stunning method used.

Striation patterns of ox muscle in rigor mortis

Ox muscle in rigor mortis offers a selection of myofibrils fixed at varying degrees of contraction from sarcomere lengths of 3.7 to 0.7 micro. A study of this material by phase contrast and electron microscopy has revealed four distinct successive patterns of contraction, including besides the familiar relaxed and contracture patterns, two intermediate types (2.4 to 1.9 micro, 1.8 to 1.5 micro) not previously well described.

Simple methods of forced oral opening for cadavers oriented to causes of fixed jaw

Forensic dentistry plays an essential role in personal identification procedures. An adequate interincisal space of relatively fresh cadavers would be required to obtain detailed dental findings. We developed novel and simple procedures of oral opening which are oriented to the causes of the fixed jaw and conscious of facial damage. Preliminary inspection disclosed three causes of the difficulty of oral opening, namely exceptional drying or parchmenting, rigor mortis and loss of extensibility of the temporalis muscles. Tenotomy on the temporalis muscles for cases with the last two factors, and/or mandibular periosteal stripping for those with the first one were employed to approach the oral cavity of cadavers, and a desired degree of interincisal opening was attained. Single or combinational operation of these methods is definitely effective to obtain odontological data without altering facial configuration.

Rigor mortis development at elevated temperatures induces pale exudative turkey meat characteristics

Development of rigor mortis at elevated post-mortem temperatures may contribute to turkey meat characteristics that are similar to those found in pale, soft, exudative pork. To evaluate this effect, 36 Nicholas tom turkeys were processed at 19 wk of age and placed in water at 40, 20, and 0 C immediately after evisceration. Pectoralis muscle samples were taken at 15 min, 30 min, 1 h, 2 h, and 4 h post-mortem and analyzed for R-value (an indirect measure of adenosine triphosphate), glycogen, pH, color, and sarcomere length. At 4 h, the remaining intact Pectoralis muscle was harvested, and aged on ice 23 h, and analyzed for drip loss, cook loss, shear values, and sarcomere length. By 15 min post-mortem, the 40 C treatment had higher R-values, which persisted through 4 h. By 1 h, the 40 C treatment pH and glycogen levels were lower than the 0 C treatment; however, they did not differ from those of the 20 C treatment. Increased L* values indicated that color became more pale by 2 h post-mortem in the 40 C treatment when compared to the 20 and 0 C treatments. Drip loss, cook loss, and shear value were increased whereas sarcomere lengths were decreased as a result of the 40 C treatment. These findings suggested that elevated post-mortem temperatures during processing resulted in acceleration of rigor mortis and biochemical changes in the muscle that produced pale, exudative meat characteristics in turkey.

Strain dependence of the elastic properties of force-producing cross-bridges in rigor skeletal muscle

Stretch and release experiments carried out on skinned single fibers of frog skeletal muscle under rigor conditions indicate that the elastic properties of the fiber depend on strain. For modulation frequencies below 1000 Hz, the results show an increase in Young's modulus of 20% upon a stretch of 1 nm/half-sarcomere. Remarkably, the strain dependence of Young's modulus decreases at higher frequencies to about 10% upon a 1-nm/half-sarcomere stretch at a modulation frequency of 10 kHz. This suggests that the cause of the effect is less straightforward than originally believed: a simple slackening of the filaments would result in an equally large strain dependence at all frequencies, whereas strain-dependent properties of the actin filaments should show up most clearly at higher frequencies. We believe that the reduction of the strain dependence points to transitions of the cross-bridges between distinct force-producing states. This is consistent with the earlier observation that Young's modulus in rigor increases toward higher frequencies.

Three-dimensional structure of nucleotide-bearing crossbridges in situ: oblique section reconstruction of insect flight muscle in AMPPNP at 23 degrees C

We have explored the three-dimensional structure of myosin crossbridges in situ in order to define the structural changes that occur when nucleotide binds to the myosin motor. When AMPPNP binds to rigor insect flight muscle, each half sarcomere lengthens by approximately 2.0 nm and tension is reduced by approximately 70% without a reduction in stiffness, suggesting partial reversal of the power stroke. We have obtained averaged oblique section three-dimensional reconstructions of mechanically monitored insect flight muscle in AMPPNP that permit simultaneous examination of all myosin crossbridges within the unit cell and direct comparison of calculated transforms with X-ray diagrams of the native fibers. Transforms calculated from the oblique section reconstruction of AMPPNP insect flight muscle at 23 degrees C show good agreement with native X-ray diagrams, suggesting that the average crossbridge forms in the reconstruction reflect the native structure. In contrast to the rigor lead and rear crossbridges in the double chevrons, the averaged reconstruction of AMPPNP fibers show only one crossbridge class, in the position of the rigor lead bridge. The portion of the crossbridge close to the thick filament appears broader than in rigor, and shows a small 0.5 to 1.0 nm M-ward shift of the regulatory domain region of myosin. In transverse view, AMPPNP "lead" crossbridges are less azimuthally bent than rigor. Fitting the atomic model of actomyosin subfragment 1 to the averaged crossbridges shows that the detectable differences between rigor bridges and between rigor and AMPPNP bridges occur in the alignment and angles of the regulatory domains and suggests that rear bridges are more strained than lead crossbridges. The apparent absence of rear bridges in AMPPNP in averaged reconstructions indicates detachment of a number of force-bearing bridges, which conflicts with the maintained stiffness of the fibers used for the reconstruction. This conflict may be explained if rigor rear bridges become distributed irregularly over more actin sites in AMPPNP, so that their average density is too low to appear in the averaged reconstructions. The reconstructions indicate that in insect flight muscle the response of in situ rigor crossbridges to AMPPNP binding is not uniform. Lead bridges persist but have altered structure in the light chain domain, whereas rear bridges detach and possibly redistribute. Shape changes in attached myosin heads within the myofibrillar lattice are in the appropriate direction and of the appropriate magnitude needed to explain the sarcomere lengthening. This could be a direct response to nucleotide binding, a passive response to rear bridge detachment, or a combination of both.

Electron tomography of insect flight muscle in rigor and AMPPNP at 23 degrees C

Treatment of rigor fibers of insect flight muscle (IFM) with AMPPNP at 23 degrees C causes a 70% drop in tension with little change in stiffness. In order to visualize the changes in crossbridge conformation and distribution that give rise to the mechanical response, we have produced three-dimensional reconstructions by tomography of both rigor and AMPPNP-treated muscle that do not average the repeating motifs of crossbridges, and thereby retain information on variability of crossbridge structure and distribution. Tomograms can be averaged when display of only the regular features is wanted. Tomograms of rigor IFM show double-headed lead and single-headed rear crossbridges. Tomograms of IFM treated with AMPPNP at 23 degrees C reveal many double-headed and some single-headed "lead" bridges but few crossbridges corresponding to the rear bridges of rigor. Instead, new non-rigor forms of variably angled crossbridges are found bound to actin sites not labeled with myosin heads in rigor. This indicates that the rear bridges of rigor have redistributed during the transition from rigor to the AMPPNP state, which could explain the maintenance of rigor stiffness despite the loss of tension. Comparison of in situ crossbridges in tomograms of rigor with atomic model of acto-S1, the complex formed by myosin subfragment 1 and actin, reveals that the regulatory domain of S1 would require significant bending and realignment to fit into both types of rigor crossbridges. The modifications are particularly significant for the rear bridges and suggest that differential strain in the regulatory domain of rear bridges may be the basis for their detachment and redistribution upon binding AMPPNP. Similar comparison using lead-type crossbridges in AMPPNP reveals departures from the rigor acto-S1 atomic model that include azimuthal straightening and a slight M-ward bending in the regulatory domain. Both the motor and regulatory domains of the new non-rigor crossbridges differ from those in the atomic model of acto-S1. A new crossbridge motif identified in AMPPNP-treated muscle consists of paired rigor-like and non-rigor crossbridges and suggests possible transitions in the myosin working stroke.

Effects of adenosine diphosphate on the structure of myosin cross-bridges: an X-ray diffraction study on a single skinned frog muscle fibre

Using a technique to obtain a detailed X-ray diffraction pattern from a single skinned frog muscle fibre, we studied the effects of ADP on the structure and arrangement of myosin heads. An imaging plate and a cooled-CCD X-ray detector were used to record the diffraction patterns. Addition of 1 mM ADP to a rigor fibre increased the intensity of the third-order meridional reflection of the myosin repeat by 50-85%. The intensity of the sixth-order meridional reflection also increased. After removing the ADP, these intensities decreased but did not return to the level before the ADP was added. No significant changes were observed in the intensities of the equatorial reflections and the actin layer-lines. These results suggest that, upon ADP binding, the conformation of a myosin head changes without detaching from actin. The structural change may involve a relative motion between domains of the myosin head by the closure of the cleft to which an ADP molecule binds.

Effect of brine injection on water dynamics in postmortem muscle: study of T2 and diffusion coefficients by MR microscopy

The dynamics of water in postmortem muscle were studied by magnetic resonance microscopy (MRM). Rabbit muscles were arterially injected with 3 and 5 M NaCl brine. T2 and diffusion mapping were performed during the onset of rigor mortis. A wide spread of T2 values and widely differing postmortem evolutions were observed for injected muscles, whereas T2 was spatially homogeneous for intact muscle. Also, highly variable spatial distribution of diffusion coefficients along (Dz) and across (Dx) the muscle fibers was observed and diffusion anisotropy Dz/Dx) was less marked in injected muscles. The results indicate heterogeneity of brine distribution far from the injection site soon after injection. The postmortem evolution of the parameters is discussed in terms of structural changes induced by brine injection. MRM provides insight into how water dynamics respond to different NaCl concentrations inside muscle.