Trace metals in muscle tissue of fish taken from the southern Baltic

The determination of Fe, Mn, Ni, Pb, Cu, Co, Zn and Cd was investigated on 123 samples of muscle tissue of cod, herring, sprat and some other species of fish caught in 1981 in the southern Baltic Sea. The ranges and mean levels of metals recorded in this paper are compared with values reported previously by other authors for cod, herring and sprat from different regions of the Baltic Sea. The correlation coefficients between the metal concentrations in cod and herring muscles were calculated. The species-dependent changes of some metals in species analysed were observed.     

Organochlorine pesticides and polychlorinated biphenyls in cod from the southern Baltic, 1983

Hexachlorobenzene (HCB), alpha-, beta-, gamma- and delta-benzenehexachloride (BHC; HCH), p,p'-DDE, o,p'-DDD, o,p'-DDT, p,p'-DDD and p,p'-DDT (sigma DDT) and polychlorinated biphenyls (PCB) levels have been determined in muscle tissue of 207 cod (Gadus morhua) netted during 1983 in different regions in the southern part of the Baltic Sea. The mean levels found for cod muscle tissue (microgram/kg) related to wet weight were: 0.65 HCB, 1.2 alpha-BHC, 9.0 beta-BHC, 2.8 gamma-BHC, delta-BHC remained undetected, 13 sigma BHC, 4.4 p,p'-DDE, o,p'-DDD and o,p'-DDT remained undetected, 4.0 p,p'-DDD, 1.8 p,p'-DDT, 10 sigma DDT and 55 PCBs. The results are compared with levels found in cod caught in different regions of the Baltic Sea during 1967-1983, and reported previously by other authors.     

Trace metals in cod from the southern Baltic, 1983

Zusammenfassung Die Konzentration von Cadmium, Blei, Kupfer, Zink, Eisen, Mangan und Nickel wurde in den Muskelgeweben von 201 Kabeljaus (Gadus morhua), gefangen in verschiedenen Regionen der südlichen Ostsee 1983, bestimmt. Die Mcßmethode war Atomabsorptions-Spektrometrie. Die mittleren erhaltenen Werte für das Frischgewicht des Muskelgewebes betrugen: 0,005 mg/kg Cd, 0,086 mg/kg Pb, 0,15 mg/kg Cu, 3,9 mg/kg Zn, 3,7 mg/kg Fe, 0,21 mg/kg Mn und 0,081 mg/kg Ni. Die Ergebnisse wurden mit den früher veröffentlichten Werten für Kabeljau und mit den anderer Autoren aus der Ostsee verglichen.Summary The cadmium, lead, copper, zinc, iron, manganese, and nickel concentrations have been determined in muscle tissue of 201 cod (Gadus morhua) netted in 1983 in different regions in the southern part of the Baltic Sea. The method of measurement was atomic absorption spectrophotometry. The mean values obtained related to wet weight (mg/kg) for cod muscle tissue were: 0.005 Cd, 0.086 Pb, 0.15 Cu, 3.9 Zn, 3.7 Fe, 0.21 Mn, and 0.081 Ni. The results are compared with values reported previously for cod from the Baltic Sea by other authors.[/p]

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Spurenelemente im Kabeljau aus der südlichen Ostsee, 1983

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Partially with financial support under grant PR-4 (Sea Fisheries Institute)     

Organochlorine pesticides and polychlorinated biphenyls in cod from the southern Baltic, 1981

98 samples of muscle tissue of cod ranging form 51 to 60 cm in total length and netted in 1981 in the southern part of the Baltic Sea were analysed for polychlorinated biphenyls (PCBs), DDT and its metabolites (DDE and DDD), hexachlorobenzene (HCB), and isomers of benzenehexachloride (alpha-, beta-, gamma- and delta-BHC). Mean values obtained related to wet weight for cod muscle tissue were: 0.77 micrograms kg/HCB, 0.71 micrograms kg/alpha-BHC, 3.8 micrograms kg/gamma-BHC, 5.2 micrograms kg/p,p'-DDe, 2.6 micrograms kg/p,p'-DDD, 2.6 micrograms kg/p,p'-DDT, 10 micrograms kg/sigma DDT and 180 micrograms kg/PCB; beta-BHC was detectable in trace amounts and delta-BHC was undetected. Generally residue levels of organochlorine pesticides and PCBs found in the muscles were low, and substantial decrease of sigma DDT and less of PCB levels in recent years when compared with data noted in 1969-1970 and 1972-1974 is noticeable.     

Liquid Loss as Effected by Post mortem Ultrastructural Changes in Fish Muscle: Cod (Gadus morhuaL) and Salmon (Salmo salar)

This study was performed in order to assess the effect of early post mortem structural changes in the muscle upon the liquid-holding capacity of wild cod, net-pen-fed cod (fed cod) and farmed salmon. The liquid-holding capacity was measured by a low speed centrifugation test. Transmission electron microscopy was used to discover ultrastructural changes both in the connective tissue and in the myofibrils. Differential scanning calorimetric thermograms of the muscle proteins were recorded to elucidate whether fundamental differences did exist between the proteins of the raw material tested. Multivariate statistics were used to explicate the main tendencies of variations in the thermograms. The salmon muscle possessed much better liquid-holding properties than the cod muscle, and wild cod better than fed cod regardless of the storage time. Both fed cod and farmed salmon, underwent the most severe structural alterations, probably caused by the low muscle pH values. The higher liquid-holding capacity of the salmon muscle was related to species specific structural features and better stability of the muscle proteins. The myofibrils of the salmon muscle were denser and intra- and extracellular spaces were filled by fat and a granulated material. The differences in thermograms of muscle from wild and fed cod were largely explained by the variations in pH. The severe liquid loss of fed cod is due to a low pH induced denaturation and shrinkage of the myofibrils. Post mortem degradation of the endomysial layer and the sarcolemma may have further facilitated the release of liquid.     

Interactions between hemoglobin and cod muscle constituents following treatment at extreme pH values

Acid and/or alkaline solubilization is a recent method developed to separate proteins from muscle foods with good functional properties. However, exposure of the muscle and its components to low pH values has been shown to promote lipid oxidation, limiting therefore the applications of this novel method. This research aimed primarily to study the physicochemical changes of the fish membranes brought about during acid or alkali solubilization processes. The effect on lipid oxidation and the possible role of the water soluble fraction of the muscle (press juice) as a potent antioxidant were also investigated. Model systems comprising minced cod muscle or cod microsomal suspensions were used. Results showed that acid or alkaline treatment (pH < 3.5 or pH > 10.5) of cod membranes significantly delayed lipid oxidation. Added triacylglycerols to washed cod system treated at low pH did not enhance hemoglobin-mediated lipid oxidation. Decreased precipitation of hemoglobin was observed with the alkali-treated membranes at all protein concentrations compared to the acid-treated and the untreated membranes. Finally, the addition of press juice to washed cod muscle tissue or to the membrane model system, significantly delayed hemoglobin lipid oxidation. PRACTICAL APPLICATION: The results of this study can be used to improve pH-shifting technologies to avoid or decrease lipid oxidation problems. Also, the use of press-juice from cod muscle as means of protecting the muscle against lipid oxidation is suggested.     

Glass Transition Values of Muscle Tissue

Reports of glass transition (Tg') values for frozen muscle tissue are not common and reported values are mostly much lower than would be expected. Tg’ values for muscle tissue and isolated proteins were studied using differential scanning calorimetry. Apparent Tg's of mackerel, cod and beef were similar (ca ?11 to ?13°C) and substantially higher than most published values (?15 to ?77°C for tuna and beef), but in accord with expectations for substances of high molecular weight. Dialyzed insoluble and soluble protein fractions from mackerel yielded apparent Tg’ values (ca ?7°C) that were similar, with both being higher than those for whole muscle. Apparent Tg’ values of ca ?7°C were determined for aqueous samples of gelatin and collagen, but none was detected for zein.     

Dioxin and dioxin-like PCB levels in cod-liver and -muscle from different fishing grounds of the North- and Baltic Sea and the North Atlantic

The contaminant levels of dioxins, dioxin-like PCBs and non dioxin-like PCBs were determined in pooled samples of cod liver and corresponding cod muscle from different fishing grounds of the North- and Baltic Sea and from East Greenland. The dependence of the contaminant concentrations was studied on cod of three different sizes caught at the same fishing ground. Samples were taken during different research trips at 11 fishing grounds of the Baltic Sea, and 3 fishing grounds of the North Sea and of East Greenland in 2006 and 2007, respectively. Cod liver from the Baltic- and the North Sea were highly contaminated. Mean concentrations were 93 and 83 ng WHO-TEQ/kg wet weight (w.w.), respectively. Cod livers from East Greenland had only low contaminant levels of 3.4 ng WHO-TEQ/kg w.w. Highest concentrations were found in livers from the Bay of Kiel. Within the same fishing area the concentrations increased with the size of the cod. The WHO-TEQ amounts of the cod fillets were below 1 ng WHO-TEQ/kg w.w. and thus within the commonly observed low range for lean fish.     

Aluminium content in edible parts of seafood

Samples of the edible parts of different fish species and of crustacean and molluscan shellfish were collected in the North Sea, the Barents Sea, the Baltic Sea, the Northeast Atlantic, and in Greenland waters. Most of the aluminium concentrations in fillets of lean and fatty fish were lower than 0.2?mg Al/kg wet weight. Exceptions were the aluminium concentrations in fillets of fish caught near an aluminium smelting plant (up to 1?mg Al/kg wet weight). Presumably a connection between the aluminium content in sea water and the fish fillets is responsible for this. The investigations of fillets of saithe, haddock, and cod with different lengths (age) showed that the aluminium levels decreased with increasing length, however, the decrease was not significant. An aluminium accumulation in muscle tissue with increasing age could not be detected. A comparison between fillets and different organs of cod showed higher aluminium concentrations in organs, especially in gills. The aluminium intake via gills, which are in continuous contact with the ambient water, is responsible for this. In the edible part of crustacean and molluscan shellfish higher aluminium concentrations (up to 5?mg Al/kg wet weight) were detected. The different feed spectrum and metabolism of these species seem to be responsible for the higher aluminium accumulation in marine crustacean and molluscan shellfish.     

ROLE OF INITIAL MUSCLE pH ON THE SOLUBILITY OF FISH MUSCLE PROTEINS IN WATER

The solubility of the myofibrillar and cytoskeletal proteins in water was determined for the muscle tissue often species offish. The flesh of six white-muscled fish had pH's at the time of processing above pH 6.6 and greater than 80% of their myofibrillar/cytoskeletal proteins were soluble in water. The flesh of three pelagic species and a shark had pH values when processed below 6.6 and the water solubility of their myofibrillar and cytoskeletal proteins was less than 40%. When the washed minced muscle of one of the white-fleshed species, cod, was exposed to low pH, the solubility of its myofibrillar and cytoskeletal proteins decreased substantially. The water solubility of the cod myofibrillar and cytoskeletal proteins could be reestablished by washing the acid-treated cod flesh with neutral salt solutions. It is suggested that pH values below 6.6 modify certain proteins which prevent the water-extractability of the rest of the myofibrillar and cytoskeletal proteins from being expressed.     

Thawed Chilled Barents Sea Cod Fillets in Modified Atmosphere Packaging-Application of Multivariate Data Analysis to Select Key Parameters in Good Manufacturing Practice

The purpose of the present study was to select key parameters in good manufacturing practice for production of thawed chilled modified atmosphere packed (MAP) cod (Gadus morhua) fillets. The effect of frozen storage temperature (−20 and −30 °C), frozen storage period (3, 6, 9 and 12 mo) and chill storage periods up to 21 d at 2 °C were evaluated for thawed MAP Barents Sea cod fillets. Sensory, chemical, microbiological and physical quality attributes were evaluated and multivariate data analysis (principal component analysis and partial least-squares regression) applied for identification of key parameters in good manufacturing practice for this product. Frozen storage of up to 12 mo had no significant effect on quality attributes and shelf-life at 2 °C was above 14 d irrespective of the time of frozen storage. As compared to a previous study with Baltic Sea, cod drip losses during chill storage was low for thawed MAP Barents Sea cod and this fish raw material seemed the more appropriate for production of thawed chilled MAP products. Frozen storage inactivation of the spoilage bacteria of Photobacterium phosphoreum was modest in Barents Sea cod, possibly due to high trimethylamine oxide (TMAO) and NaCl contents.     

EVALUATION OF DIFFERENT METHODS TO ISOLATE COD (GADUS MORHUA) MUSCLE MYOSIN

Four methods developed for fish muscle myosin isolation were evaluated for their potential to isolate myosin from cod white muscle. A slightly modified version of the method by Martone and coworkers (Martone et al. 1986) gave outstanding myosin purity (97.3%) as determined by SDS‐PAGE and densito‐metric analysis without employing time consuming chromalographic separation, while the other three methods tested gave myosin purity ranging from 33.4–76.75% with substantial contamination of actin and tropomyosin. The method of Manone and coworkers (1986) with more complete muscle tissue disintegration and prolonged extraction steps than used in the original work is therefore highly recommended far researchers interested in studying functionality of a pure cod myosin preparation.     

The assessment of organic mercury in Baltic fish by use of an in vitro digestion model

The organic mercury content of five commercially valuable fish species (cod, flounder, turbot, perch and herring) was determined by use of an invitro digestion model in order to assess health risk of fish caught within the Polish Exclusive Economic Zone of the Baltic Sea. Concentrations of total mercury and organic mercury were measured in the muscle tissue of fish and in the products of two-stage gastrointestinal digestion, using atomic absorption spectroscopy (AMA 254). The highest concentrations of organic mercury were found in the muscles of predatory fish that dwell in near-bottom waters. Based on a bioaccessibility estimate obtained from the in vitro digestion model, it was found that only 26-62% of organic mercury, depending on the species of fish, was released into the intestinal lumen during the digestion of muscle. Therefore, to postulate the potential toxicity of fish, based on the organic mercury content of the muscle tissue ingested by consumers, is unfounded. The risk assessment should be carried out on the basis of another parameter - the bioaccessibility of organic mercury.     

Compounds of parasitic roundworm absorbing in the visible region: target molecules for detection of roundworm in Atlantic cod

The objective of this study was to contribute to the development of technology that will be able to replace manual operations in processing of fish fillets. Removal of parasites, black lining, remnants of skin, and bloodstains are costly and time-consuming operations to the fish processing industry. The presence of parasites in fish products tends to spoil consumers' appetites. Recent reports questioning the safety of eating cod infected with parasites might lower consumer acceptance of seafood. Presently, parasites are detected and removed manually. An average efficiency of about 75% under commercial conditions has been reported. In this study, we focused on biochemical differences between cod muscle and the prevalent anisakine nematode species (Anisakis simplex and Pseudoterranova decipiens) infecting Atlantic cod (Gadus morhua). Using reversed phase high-performance liquid chromatography equipped with a photodiode array detector, substances absorbing in the range 300 to 600 nm were identified in extracts from parasite material. These substances were not detected in extracts from cod tissue. Significant biochemical differences between cod muscle and parasite material have thus been demonstrated.     

Proteolytic activity in cod (Gadus morhua) muscle during salt curing

The proteolytic activity of alkaline and acidic proteases in muscle from cod (Gadus morhua) was determined during salt curing. Proteolytic activity was determined for cod muscle that was either ice-stored or frozen-stored before it was subjected to three different salt treatments. The activity of the proteases chymotrypsin, trypsin, collagenase, elastase and cathepsin B/L was determined by the use of different fluorogenic substrates, while the total activity of acidic proteases was determined using haemoglobin as a substrate. The results indicated that the activity of the chymotrypsin, trypsin, collagenase and elastase was stimulated with increasing salt concentration, but seemed to decline again as the salt curing proceeded. Haemoglobin-hydrolysing activities, however, seemed to decrease with increasing concentration of salt in the muscle tissue.     

Parvalbumin in fish skin-derived gelatin: is there a risk for fish allergic consumers?

The major allergen parvalbumin was purified from cod muscle tissues, and polyclonal antibodies were raised towards it. The antibodies were tested for specificity and an enzyme-linked immunosorbent assay (ELISA) was developed using these antibodies. The ELISA was applied to measure parvalbumin in cod skin, the starting material for fish gelatin made from deep sea, wild fish. The ELISA was sufficiently sensitive (LLOQ?=?0.8?ng?ml(-1) in extracts, corresponding to 0.02?μg of parvalbumin per g of tissue), and did not cross-react with common food constituents. Fish gelatin, wine and beer, matrices for the potential use of this ELISA, did not cause disturbance of the assay performance. The data show that the parvalbumin content in cod muscle tissue is 6.25?mg?g(-1), while the skins contained considerably less, 0.4?mg?g(-1). Washing of the skins, a common industrial procedure during the manufacturing of fish gelatin, reduced the level of parvalbumin about 1000-fold to 0.5?μg?g(-1), or 0.5?ppm. From 95 commercial lots of fish gelatin it is shown that 73 are below 0.02?μg?g(-1) parvalbumin. From the other 22 lots, the one with the highest concentration contained 0.15?μg?g(-1) of parvalbumin. These levels are generally assumed to be safe for fish-allergic individuals.     

Organochlorine pesticides and polychlorinated biphenyls in livers of cod from the southern Baltic, 1983

Hexachlorobenzene (HCB), alpha-, beta-, gamma- and delta-benzenehexachloride (BHC; HCH), p,p'-DDE, o,p'-DDD, o,p'-DDT, p,p'-DDD and p,p'-DDT (sigma DDT) and polychlorinated biphenyls (PCB) levels have been determined in livers of 210 cod (Gadus morhua) netted during 1983 in a different regions in the southern part of the Baltic Sea. The mean levels found for cod livers related to wet weight (mg/kg) were: 0.096 HCB, 0.15 alpha-BHC, beta-BHC was found in trace amounts, 0.098 gamma-BHC, delta-BHC remained undetected, 0.26 sigma BHC, 1.1 p,p'-DDE, o,p'-DDD and o,p'-DDT remained undetected, 1.1 p,p'-DDD, 0.39 p,p'-DDT, 2.6 sigma DDT and 7.2 PCB. The levels of sigma DDT, sigma BHC and HCB found are comparable with those noted in livers taken from cod of the same length class and netted in 1981, whilst-for PCB somewhat lower levels were found. Because of heavy contamination with PCBs, sigma DDT, sigma BHC and HCB the livers of cod caught in Baltic Sea still remain insuitable for human consumption.     

Trace metals in herring from the southern Baltic, 1983

The cadmium, lead, copper, zinc, iron, manganese and nickel concentrations have been determined in muscle tissue of 187 herring (Clupea harengus) netted in different regions in the southern part of the Baltic Sea. The method of measurement was atomic-absorption spectrophotometry. The mean values obtained related to wet weight (mg/kg) for herring muscle tissue were: 0.009 Cd, 0.079 Pb, 0.49 Cu, 9.2 Zn, 9.9 Fe, 0.19 Mn and 0.10 Ni. Some differences in the concentration of particular trace metals between herring stocks sampled have been observed. The mean content of cadmium and lead in muscles of herring examined were below recommended tolerance levels of 0.05-2.0 and 0.5-2.0 mg/kg, respectively. A small number of herring contained cadmium in their muscles at a concentration above 0.05 mg/kg. The results are compared with values reported previously for Baltic herring by other authors.     

Effects of perimortem stress on farmed Atlantic cod product quality: a baseline study

The potential effects of handling stress on the product quality of farmed Atlantic cod were studied in a controlled experiment (fish anesthetized with metomidate or isoeugenol, or subjected to stress by chasing for 30 min). For comparison, stress and fillet quality was also studied for commercially slaughtered farmed cod (fish sampled from waiting cage, after pumping and stunning with carbon dioxide, and after bleeding and chilling). Baseline values for stress-related parameters (blood chemistry, muscle high-energy phosphates and inosine monophospate, initial pH, muscle twitches, and rigor mortis) of rested Atlantic cod have been established. Since our stress bout showed that this species was not easily excitable, we were less convinced that we actually did study the other extreme, namely, exhausted fish. Nevertheless, the present data from the commercial slaughter of cod suggested that our stress bout was of adequate magnitude to represent potential poor handling routines. Our results consistently showed largely no differences between treatments, and that perimortem handling stress did not cause inferior flesh quality. This suggested that farmed cod can be processed with little risk of reducing product quality (quality index, fillet water content, water-holding capacity, ultimate pH, adenosine triphosphate-related degradation products and K-value, skin and fillet color, water and salt-soluble proteins, hardness, and gaping). For better maintenance of skin appearance after storage, the importance of storing the gutted cod on the belly, avoiding direct contact between skin and crushed ice, is demonstrated.     

COMPARISON OF THREE METHODS OF FORMALDEHYDE DETERMINATION ON FROZEN SOLE, POLLOCK, HADDOCK AND COD FILLETS

The Merchoquant test strip and a rapid, enzymatic method were evaluated for the quantitation of formaldehyde (HCHO) in neutralized perchloric acid (HC10₄) extracts of fish muscle. Compared with the standard colorimetric Cochin and Axelrod (1959) modification of the Nash reagent method (1953), the nonglutathione dependent formaldehyde dehydrogenase (EC 1.2.1.46) method based on that of Yasuhara et al. (1982) for creatine was faster and less affected by interferences. The enzyme method resulted in lower HCHO values than did the modified Nash method for the gadoid pollock, haddock and cod samples while the semi-quantitative Merchoquant test strip resulted in positive readings for only one cod sample. Seventy-nine HC10₄fish extracts analyzed by the enzyme and modified Nash procedures showed a species dependent correlation between the two methods, with slopes of 0.847, 0.321, 0.436, 0.519 for sole, pollock, haddock and cod, respectively. The HCHO content of the samples ranged between 0.4 and 75 μmoles%. Standard addition evaluation of the accuracy of the formaldehyde dehydrogenase method compared with the modified Nash procedure on three samples also resulted in species dependent slopes. Nongadoid sole samples showed the greatest deviation while cod was the only species where the modified Nash method resulted in HCHO values lower than those attained with the enzyme method. The detection limit of the formaídehyde dehydrogenase method was 0.3 μmoles%.