Injection-salting of pre rigor fillets of Atlantic salmon (Salmo salar)

ABSTRACT:  The effects of temperature (−1, 4, and 10 °C), brine concentration (12% and 25% NaCl), injection volumes, and needle densities were investigated on fillet weight gain (%), salt content (%), fillet contraction (%), and muscle gaping in pre rigor brine-injected fillets of Atlantic salmon ( Salmo salar ). Increased brine concentration (12% to 25%) significantly increased the initial (< 5 min after injection) and final contraction (24 h after injection) of pre rigor fillets. Increased brine concentration significantly reduced weight gain and increased salt content but had no significant effect on muscle gaping. The temperatures tested did not significantly affect weight gain, fillet contraction, or gaping score. Significant regressions ( P < 0.01) between the injection volume and weight gain (range: 2.5% to 15.5%) and salt content (range: 1.7% to 6.5%) were observed for injections of pre rigor fillets. Double injections significantly increased the weight gain and salt content compared to single injections. Initial fillet contraction measured 30 min after brine injection increased significantly ( P < 0.01) with increasing brine injection volume but no significant difference in the fillet contraction was observed 12 h after brine injection (range: 7.9% to 8.9%). Brine-injected post rigor control fillets obtained higher weight gain, higher salt content, more muscle gaping, and significantly lower fillet contraction compared to the pre rigor injected fillets.
Injection-salting is an applicable technology as a means to obtain satisfactory salt contents and homogenously distribute the salt into the muscle of pre rigor fillets of Atlantic salmon before further processing steps such as drying and smoking.     

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.     

Injection‐Salting and Cold‐Smoking of Farmed Atlantic Cod (Gadus morhua L.) and Atlantic Salmon (Salmo salar L.) at Different Stages of Rigor Mortis: Effect on Physical Properties

ABSTRACT: Processing of fish is generally conducted postrigor, but prerigor processing is associated with some potential advantages. The aim of this study was to study how 5 processing regimes of cold‐smoked cod and salmon conducted at different stages of rigor influenced yield, fillet shrinkage, and gaping. Farmed cod and salmon was filleted, salted by brine injection of 25% NaCl, and smoked for 2 h at different stages of rigor. Filleting and salting prerigor resulted in increased fillet shrinkage and less increase in weight during brine injection, which in turn was correlated to the salt content of the fillet. These effects were more pronounced in cod fillets when compared to salmon. Early processing reduced fillet gaping and fillets were evaluated as having a firmer texture. In a follow‐up trial with cod, shrinkage and weight gain during injection was studied as an effect of processing time postmortem. No changes in weight gain were observed for fillets salted the first 24 h postmortem; however, by delaying the processing 12 h postmortem, the high and rapid shrinking of cod fillets during brine injection was halved.     

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.     

The role of collagen in the quality and processing of fish

Collagen in the muscles of fish constitutes the main component of the connective tissue membranes joining individual myotomes and is responsible for the integrity of the fillets. The content of collagen in fish muscles is from about 0.2 to 1.4% and in squid mantel about 2.6%. Fish and invertebrata collagens contain slightly more essential amino acids than intramuscular bovine connective tissue collagen. The invertebrata collagens are exceptionally rich in sugars linked mainly O-glycosidically to hydroxylysine residues. During maturation of fish the proportion of collagen to total protein in the muscles increases while the extent of crosslinking does not change significantly. The thermal properties of fish collagens depend significantly on the content of hydroxyproline and proline residues which in turn is correlated to the temperature of the habitat. Generally the shrinkage temperature of fish skin collagens is about 20 degrees C lower than that of mammalian hide collagens. In several species of fish the weakening of the connective tissues post mortem may lead to serious quality deterioration that manifests itself by disintegration of the fillets, especially under the strain of rough handling and of rigor mortis at ambient temperature. Thermal changes in collagen are the necessary result of the cooking of fish, squid, and minced fish products and contribute to the desirable texture of the meat. However, they may lead to serious losses during hot smoking due to a reduction in the breaking strength of the tissues when heating is conducted at high relative humidity. Because of the high viscosity of gelatinized collagen, it is not possible to concentrate the fish stickwaters, a proteinaceous byproduct of the fish meal industry, to more than 50% dry matter. Better knowledge of the contents and properties of fish collagens could be helpful in rationalizing many aspects of fish processing.     

Computer Vision Detection of Salmon Muscle Gaping Using Convolutional Neural Network Features

Salmon muscle gaping will lead to the irregular voids or undesirable lace-like appearance in the final product. This study was carried out to develop an automatic imaging analysis method for rapid, accurate, and non-invasive detection of gaping blemishes on salmon carcasses. Salmon fillets could be classified as wholesome or defective samples based on the number of candidate gaping regions in the preliminary step applying local adaptive thresholding. Supervised classification results were compared between using histograms of oriented gradients (HOG) and convolutional neural network (CNN) feature extractors. It was shown that CNN features outperformed HOG features with correct classification rates (CCRs) of 0.927 and 0.916 for cross validation and test data set, respectively. Relieff was then applied to select important feature attributes by reducing the 4096-dimensional to 239-dimensional vector. Simplified CNN model also yielded good classification performance with CCR of 0.925 for cross validation. Therefore, CNNs were used to extract features from candidate regions and then reduced features to the 239-dimensional vector. The resultant vector was fed to the simplified CNN model to make a final decision. The prediction maps for visualizing the classification result on salmon fillet were subsequently generated. The overall results confirmed that this proposed method is effective and suitable for the muscle gaping detection. Future work will be focused on applying this method in packing plants where fish fillets are progressing rapidly, and promising results will allow the identification of critical points in the supply chain that impact upon product quality.     

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.     

Computer vision-based evaluation of pre- and postrigor changes in size and shape of Atlantic cod (Gadus morhua) and Atlantic salmon (Salmo salar) fillets during rigor mortis and ice storage: effects of perimortem handling stress

The present study describes the possibilities for using computer vision-based methods for the detection and monitoring of transient 2D and 3D changes in the geometry of a given product. The rigor contractions of unstressed and stressed fillets of Atlantic salmon (Salmo salar) and Atlantic cod (Gadus morhua) were used as a model system. Gradual changes in fillet shape and size (area, length, width, and roundness) were recorded for 7 and 3 d, respectively. Also, changes in fillet area and height (cross-section profiles) were tracked using a laser beam and a 3D digital camera. Another goal was to compare rigor developments of the 2 species of farmed fish, and whether perimortem stress affected the appearance of the fillets. Some significant changes in fillet size and shape were found (length, width, area, roundness, height) between unstressed and stressed fish during the course of rigor mortis as well as after ice storage (postrigor). However, the observed irreversible stress-related changes were small and would hardly mean anything for postrigor fish processors or consumers. The cod were less stressed (as defined by muscle biochemistry) than the salmon after the 2 species had been subjected to similar stress bouts. Consequently, the difference between the rigor courses of unstressed and stressed fish was more extreme in the case of salmon. However, the maximal whole fish rigor strength was judged to be about the same for both species. Moreover, the reductions in fillet area and length, as well as the increases in width, were basically of similar magnitude for both species. In fact, the increases in fillet roundness and cross-section height were larger for the cod. We conclude that the computer vision method can be used effectively for automated monitoring of changes in 2D and 3D shape and size of fish fillets during rigor mortis and ice storage. In addition, it can be used for grading of fillets according to uniformity in size and shape, as well as measurement of fillet yield measured in thickness. The methods are accurate, rapid, nondestructive, and contact-free and can therefore be regarded as suitable for industrial purposes.     

Salmon Fillet Texture is Determined by Myofiber-Myofiber and Myofiber-Myocommata Attachment

ABSTRACT: Atlantic salmon ( Salmo salar ) fillets were stored on ice for a maximum of 14 d to determine which muscle structures are associated with changes in texture and rigor. Texture was measured as shear force and the changes correlated with structural alterations. Texture decreased significantly within 24 h in parallel with loss of attachment of muscle fibers. Loss of rigor stiffness by 5 d was associated with myofiber detachment from the myocommata. These results show that fillet texture depends on several distinct structures and events, initially including breaks in the cell cytoskeleton and loss of fiber-fiber attachment and later breaks in the connective tissue and fiber detachment from the myocommata.     

CHEMICAL COMPOSITION AND POSTMORTEM CHANGES IN SOFT TEXTURED MUSCLE FROM INTENSELY FEEDING ATLANTIC COD (GADIUS MORHUA, L)

Soft textured fillets from postspawning Atlantic cod caught during the influx of capelin exhibited significantly more drip than fillets from fish caught at other times of the 1983 inshore fishing season. The extent and rate of pH decline, protein, collagen and temperature of the muscle were not distinctive in fish caught during the influx of capelin. The muscle from these fish were unique in exhibiting a rapid and relatively low ultimate pH together with a stable pH after the onset of rigor mortis. The number of capelin present in the stomach of cod at the time of catch was positively related (r = 0.92) to the amount of free drip recovered from the fillets.