Effects of Rigor Mortis on Gel-forming Properties of Surimi and Unwashed Mince Prepared from Tilapia

Quality of surimi and unwashed fish (tilapia, Areochromis aureus) mince was investigated as affected by development of rigor mortis in fish prior to processing. Significantly higher protein content and yield, reduced cook loss, and enhanced gel-forming ability and protein ex-tractability were associated with surimi produced from pre-rigor fish. Gels prepared from unwashed minced muscle exhibited less cook-loss pre-rigor, but stage of rigor had little effect on gel Theological properties and protein extractability. Thermal rigidity scanning and differential scanning calorimetry showed substantially higher rigidity values and enthalpies of denaturation, respectively, for surimi prepared from pre-rigor fish, but no effect on transition temperatures due to stage of rigor.     

The Effect of Stunning Methods on Rigor Mortis and Texture Properties of Atlantic Salmon (Salmo Salar)

Shear force and rigor mortis were used to evaluate the post‐mortem changes of muscle texture in Atlantic salmon (Salmo salar). The fish were either stunned with carbon dioxide (CO₂), electricity, or percussion prior to slaughter. The pre‐mortem stress during CO₂ stunning resulted in an earlier onset and resolution of rigor mortis, and accelerated post‐mortem softening of the muscle tissue as compared to the other stunning methods. No significant differences, either in development of rigor mortis or shear force, were seen between fish that were stunned with electricity or by percussion. Consequently electricity can be used for stunning fish prior to slaughter.     

Muscle Fiber–Connective Tissue Junctions in the Fish Blue Grenadier (Macruronus novaezelandiae). A Scanning Electron Microscope Study

The junctions between the muscle fibers and the connective tissue of blue grenadier (Macruronus novaezelandiae Hector) were studied using scanning electron microscopy. In fish before, during, and just after rigor mortis, the muscle fibers are attached to the myocommatal connective tissue sheets by fine collagenous fibrils. After chilled storage these fibrils deteriorate and the muscle fibers gradually detach from the myocommata. It appears that the fibrils are destroyed by endogenous collagenases and/or other proteinases.     

NUCLEOTIDE CATABOLISM AND CHANGES IN TEXTURE INDICES DURING ICE STORAGE OF CULTURED STURGEON, ACIPENSER TRANSMONTANUS

ABSTRACT ATP depletion and other biochemical changes were related to texture indices of cooked sturgeon meat from struggled and anesthetized fish. The rates of ATP depletion, pH decline and time of rigor onset were slow in both sturgeon groups compared to other finfish. ATP depletion and accumulation of inosine and hypoxanthine were significantly faster in sturgeon allowed to struggle before death than in anesthetized fish. Penetrometer tests revealed that cooked sturgeon meat was firmer prior to ATP depletion and the onset of rigor than in the postrigor state. Fish allowed to struggle prior to death had a softer cooked meat than anesthetized fish during the first few days of iced storage. Compression tests showed that texture of cooked meat was firmest when the muscle was in rigor and also showed that meat from struggled fish was softer than that from anesthetized fish. These findings suggested that the tough texture problem, sometimes observed in farmed sturgeon, may be minimized by allowing the sturgeon meat to go through rigor prior to cooking.     

ATP, IMP, and Glycogen in Cod Muscle at Onset and During Development of Rigor Mortis Depend on the Sampling Location

ABSTRACT: Variation in glycogen, ATP, and IMP contents within individual cod muscles were studied in ice stored fish during the progress of rigor mortis. Rigor index was determined before muscle samples for chemical analyzes were taken at 16 different positions on the fish. During development of rigor, the contents of glycogen and ATP decreased differently in relation to rigor index depending on sampling location. Although fish were considered to be in strong rigor according to the rigor index method, parts of the muscle were not in rigor as high ATP concentrations were found in dorsal and tail muscle.     

Effect of Storage Temperature on Rigor-Mortis and ATP Degradation in Plaice Paralichthys olivaceus Muscle

Live specimens of the plaice Paralichthys olivaceus were spiked at the brain, stored at various temperatures ranging from 0° to 20°C and examined for changes in rigor tension and ATP degradation in the muscle. The ATP degradation rate was clearly slower at 5–15°C than at WC, resulting in retardation of rigor- mortis onset at the former temperatures. Lactic acid accumulation in the muscle correlated well with the decrease of ATP. The muscle showed an ATP concentration of 3 μmol/g and “rigor index” (full rigor = 100%) at 30% when lactic acid increased up to 30 μmol/g at most storage temperatures. The muscle showed full rigor when ATP completely disappeared and lactic acid attained the maximum plateau (40–50 μmol/g).     

A Simple Method for Following Postmortem ATP Depletion in Lamb Muscle

Relationship between adenosine 5′-triphosphate (ATP) concentration and R-value, defined as the absorption ratio of the degradation derivatives inosine 5′-monophosphate (IMP), inosine and hypoxanthine (E₂₅₀) to adenosine nucleotides (E₂₆₀), was studied in postmortem lamb Longissimus dorsi, until onset of rigor mortis, at different temperatures of muscle storage and lamb carcass weight. Results showed a high overall correlation coefficient (r =?0.960), nondependent of storage temperature or carcass weight. Thus, lamb postmortem ATP concentrations can be indirectly calculated through a simple, rapid, economic and reliable method such as R-value measurements.     

Flesh Quality in Snapper, Pagrcrs auratus, Affected by Capture Stress

Muscle metabolites in resting, tank acclimated snapper, Pagrus auratus, were monitored for 72 hr postmortem and compared with values from exercised or commercially caught fish. The physiological status of the live animal was quantified by plasma cortisol and blood chemistry. Cortisol levels were lowest in unstressed controls (6.8 ± 2.1 ng mL^?1) while exercised laboratory fish had highest levels (67.7 ± 11.2 ng mL^?1). Control fish maintained a constant K-value for 72 hr in chilled storage; all other groups had significant increases. Onset of rigor development and muscle ATP depletion was delayed in unstressed fish and was more rapid in line-captured than exercised fish. Commercial users minimizing stress would maintain high flesh quality.     

The connective tissues of fish.

'Gaping' is a phenomenon in which the connective tissues of fish fillets fail to hold the blocks of muscle together. Slits appear across the surface of the muscle which cannot then be mechanically skinned, or, in the case of smoked salmon fillets, sliced.
Seasonal increases in the gaping of salmon fillets coincide with a fall in the postmortem pH of the flesh, occurring in June-July.
Extensive gaping can be caused by fish entering rigor mortis at too high a temperature. In trout, this temperature is considerably higher than in gadoids, suggesting that gaping from high-temperature rigor may in practice be fairly rare in salmonids.
The thermal denaturation temperature ( T _D) of acid-soluble collagen isolated from the turbot farmed in warmed water does not differ significantly from that of the connective tissues of those reared at normal temperatures. This observation is discussed in relation to gaping.     

The effect of myofibrillar/sarcoplasmic protein ratios on the properties of round scad muscle protein based film

The effect of the ratios of myofibrillar protein (MP) to sarcoplasmic protein (SP) from round scad (Decapterus maruadsi) muscle on the properties of the resulting films was investigated. Tensile strength (TS) of films decreased with increasing SP content (p < 0.05). Films prepared from MP/SP ratio of 10:0 (w/w) exhibited the highest TS (p < 0.05). Elongation at break (EAB) of films prepared with SP content greater than 30% had the decreased EAB (p < 0.05). Water vapor permeability (WVP) of films increased when SP content increased up to 20% and decreased with increasing SP content up to 30% (p < 0.05). Solubility of films decreased but protein solubility increased with increasing SP contents (p < 0.05). The a*-value and ΔE* of film increased with increasing SP content. Films with all MP/SP ratios exhibited the negligible transmission to the light in UV range. Therefore, it is suggested that the type and ratio of proteins in fish muscle, both SP and MP, influenced the properties of film from round scad muscle. Results suggested that the removal of sarcoplasmic protein from fish muscle by thorough washing was an effective means to improve the mechanical properties as well as color of the fish muscle protein-based film.     

Location of and post‐mortem changes in some cytoskeletal proteins in pork and cod muscle

The cytoskeletal proteins actin, nebulin, spectrin, desmin, vinculin and talin were labelled immunohistochemically in sections of muscle from commercially available pigs and cod (Gadus morhua) taken pre‐rigor and from samples stored for several days. Actin, nebulin and spectrin gave similar labelling patterns in both pork and cod muscle which remained the same in stored samples. Desmin was intensely labelled at the cell boundaries and within the body of the cells in both pork and cod in the initial and the stored samples. Vinculin was readily labelled in pork muscle but showed only diffuse labelling in fish. Labelling for talin in pork muscle was intense at the sarcolemma but was not present in samples stored for 4 days. In contrast, the label for talin was concentrated at the myotendinous junction of the cod muscle throughout the storage period. These are the first reports of the detection and location of spectrin and vinculin in fish muscle and of the location of talin. The results are discussed in terms of muscle structure, function and post‐mortem tenderisation. © 2000 Society of Chemical Industry     

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°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 δE 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 Rigor Status during High‐Pressure Processing on the Physical Qualities of Farm‐Raised Abalone (Haliotis rufescens)

High‐pressure processing (HPP) is used to increase meat safety and shelf‐life, with conflicting quality effects depending on rigor status during HPP. In the seafood industry, HPP is used to shuck and pasteurize oysters, but its use on abalones has only been minimally evaluated and the effect of rigor status during HPP on abalone quality has not been reported. Farm‐raised abalones (Haliotis rufescens) were divided into 12 HPP treatments and 1 unprocessed control treatment. Treatments were processed pre‐rigor or post‐rigor at 2 pressures (100 and 300 MPa) and 3 processing times (1, 3, and 5 min). The control was analyzed post‐rigor. Uniform plugs were cut from adductor and foot meat for texture profile analysis, shear force, and color analysis. Subsamples were used for scanning electron microscopy of muscle ultrastructure. Texture profile analysis revealed that post‐rigor processed abalone was significantly (P < 0.05) less firm and chewy than pre‐rigor processed irrespective of muscle type, processing time, or pressure. L values increased with pressure to 68.9 at 300 MPa for pre‐rigor processed foot, 73.8 for post‐rigor processed foot, 90.9 for pre‐rigor processed adductor, and 89.0 for post‐rigor processed adductor. Scanning electron microscopy images showed fraying of collagen fibers in processed adductor, but did not show pressure‐induced compaction of the foot myofibrils. Post‐rigor processed abalone meat was more tender than pre‐rigor processed meat, and post‐rigor processed foot meat was lighter in color than pre‐rigor processed foot meat, suggesting that waiting for rigor to resolve prior to processing abalones may improve consumer perceptions of quality and market value.     

Mercury and selenium concentrations in muscle tissue of different species of predatory freshwater fish and correlation between these elements

Concentrations of total mercury and selenium were determined in 49 and 42 muscle tissue samples, respectively, of six species of predatory freshwater fish, dace (Leuciscus leuciscus), pike perch (Sander lucioperca), pike (Esox lucius), European catfish (Silurus glanis), rainbow trout (Oncorhynchus mykiss) and asp (Aspius aspius). Muscle selenium concentration did not correlate with the corresponding total mercury concentration (R ^2?<?0.198) in all examined predatory fish species. There was an inverse correlation between the ratio Se/Hg content and the total mercury content in the muscle tissues of dace, pike perch, pike, European catfish and asp. The muscle tissue of rainbow trout exhibits a linear correlation between the ratio Se/Hg content and the total mercury content. The total mercury concentration of all examined samples did not exceed the hygienic limit for Hg for predatory fish.     

The connective tissues of fish

Summary. 'Gaping'is a phenomenon in which slits or holes appear between the muscle blocks, so that in a bad case the fillet falls to pieces and cannot be processed or sold. the gaping in whole fish frozen in rigor mortis, thawed and filleted was shown to be related to the biological condition of the fish, strong healthy fish gaping a great deal, while spent or starving fish did not gape at all. It is postulated that when fish are frozen in rigor mortis the ice growing in the connective tissue weakens it, so that it may break under the rigor mortis contraction. the contraction of spent or starving fish appears to be too weak to break the connective tissue. No gaping was shown by similar fish frozen before rigor mortis. the practical importance of the findings is discussed.     

TEXTURE OF FISH MUSCLE

Morphological and chemical aspects of fish muscle texture are reviewed and differences from red meat are pointed out. A unique feature of fish muscle is its low connective tissue content which accounts for easy disintegration of fish flesh on heating. Thus, the muscle fibers are the main textural elements in cooked fish meat. Because of this, most of the popular texture testing instruments are not applicable to fish. Best results are obtained with the thin blade shear/compression cell.
Texture of fish muscle is affected by the species, age and size of the fish within the species, and nutritional state. Postmortem factors influencing texture include glycolysis, rigor mortis and the accompanying contraction of the muscle often leading to the separation of muscle segments (gaping), temperature profile during storage, temperature of cooking, pH and presence of NaCl.     

Rigor Mortis Assessment of Atlantic Salmon (Salmo Salar) and Effects of Stress

The rigor mortis development of large Atlantic salmon was evaluated at a commercial plant using a sensory method, a mechanical rigorometer and low-frequency vibrations. The fish were classified according to rigor state using a neural network. Assessments were done with fish subjected to two different levels of handling stress prior to slaughter. White muscle high-energy phosphates and inosine monophosphate were used as indices of stress showing that handling stress may be considerable during commercial slaughter. Results indicate rigor assessment should be nondestructive and classificaton of rigor state was possible using a lowfrequency vibration method combined with a neural network.     

The influence of temperature on shortening and rigor onset in beef muscle

At sufficient ATP concentration and temperatures below about 15°C, pre-rigor beef muscles (neck muscles) contract; this phenomenon is known as cold shortening. There is also a contracture at higher temperatures occurring just before rigor onset which is called rigor shortening. While rigor shortening starts in neck muscles at pH around 6·3–6·0 and at about 2 μMol ATP/g muscle, cold shortening can begin at pH around 7·0 and the full ATP concentration (4 μMol ATP/g) in the muscle. Shortening can take place as long as there is no irreversible formation of the actomyosin complex in the muscle, i.e. before rigor onset occurs, which can be measured by intermittent loading of the muscle. The degree of extensibility which follows starts to decrease at the moment of rigor onset. This irreversible loss of extensibility at temperatures between the freezing point (?1°C) and physiological temperatures (38°C) starts at various pH values and ATP concentrations in the muscle. At 38°C the rigor onset occurs at pH 6·25 and about 2 μMol ATP/g muscle, dropping at 15°C to pH 5·75 and 1 μMol ATP/g muscle. At 0°C, as at all temperatures below 10°C, the loss of extensibility at medium loads (about 250 g/cm²) begins shortly after cold shortening. This loss of extensibility is reversible by increasing the load or raising the temperature. The irreversible loss, or rigor onset, however, occurs at 0°C with pH of 6·1–6·2 and 1·8–2·0 μMol ATP/g muscle. Thus, the onset of rigor is influenced by more than one factor. Temperature, pH and ATP concentration each play a rôle.Maximum loss of extensibility or completion of rigor is reached between 10°C and 38°C at pH 5·5–5·6 and less than 0·5 μMol ATP/g muscle. At 0°C the completion of rigor takes place at pH 6·0, but still at 0·5 μMol ATP/g muscle. The latter fact shows that the completion of rigor is solely dependent on the ATP concentration in the muscle; nevertheless, the pH of rigor completion is higher in the extreme cold shortening range. This is apparently due to a different pH/ATP relationship in muscles at low temperatures.The results are discussed in terms of changes in the concentration of Ca²⁺ ions and ATP.The results are of particular interest for the handling of hot-boned meat; that is, for both the cooling of pre-rigor muscle and the use of hot-boned meat for processing.     

Atlantic salmon skin and fillet color changes effected by perimortem handling stress, rigor mortis, and ice storage

ABSTRACT:  The changes in skin and fillet color of anesthetized and exhausted Atlantic salmon were determined immediately after killing, during rigor mortis, and after ice storage for 7 d. Skin color (CIE L *, a *, b *, and related values) was determined by a Minolta Chroma Meter. Roche Salmo Fan™ Lineal and Roche Color Card values were determined by a computer vision method and a sensory panel. Before color assessment, the stress levels of the 2 fish groups were characterized in terms of white muscle parameters (pH, rigor mortis, and core temperature). The results showed that perimortem handling stress initially significantly affected several color parameters of skin and fillets. Significant transient fillet color changes also occurred in the prerigor phase and during the development of rigor mortis. Our results suggested that fillet color was affected by postmortem glycolysis (pH drop, particularly in anesthetized fillets), then by onset and development of rigor mortis. The color change patterns during storage were different for the 2 groups of fish. The computer vision method was considered suitable for automated (online) quality control and grading of salmonid fillets according to color.     

Effects of Brain Destruction on Post Harvest Muscle Metabolism in the Fish Kahawai (Arripis trutta)

Brain destruction followed by immediate chilling of troll-caught kahawai delayed the onset of rigor by 73 min. It also resulted in the lowest measured pH in white muscle during rigor being reached after 1500 min compared with only 500 min for untreated fish. This difference in pH appeared to correlate with differences in lactic acid levels during rigor. Brain destruction also considerably increased the time at which significant amounts of ATP could be found in white muscle. High pH and ATP levels particularly during the chilling phase may contribute to retention of flesh translucency for longer periods.