High pressure treatment effects on cod (Gadus morhua) muscle

After treatment at pressures above 400 MPa, the oxidative stability of the lipids in cod (Gadus morhua) muscle were markedly decreased as measured by the thiobarbituric acid (TBA) number. This was thought to be due to the release of metal catalysts from complexes, since addition of EDTA effectively inhibited the increased rates of oxidation. As judged by differential scanning calorimetry and electrophoresis this effect did not appear to be related to denaturation of the major proteins in meat, since myosin was denatured at 100–200 MPa and actin and most of the sarcoplasmic proteins at 300 MPa. A few water soluble proteins survived pressures of 800 MPa including several of the proteases, but there was a marked decrease in activity of the neutral proteases (pH optima 6.6) above 200 MPa. In contrast to heat-treatment, pressure was shown to lead to the formation of structures that were stabilised, at least to some extent, by hydrogen bonds and texture profile analysis (TPA) showed that the structures produced by heat and pressure treatments had very different textures.     

The effects of various salt concentrations during brine curing of cod (Gadus morhua)

The method used for salting of cod (Gadus morhua) is believed to influence the quality and characteristics of the final product. In recent years an initial brine salting for 1–4 days has preceded dry salting; this increases both the weight yield and quality of the final product. After removal from the brine, dry salting is followed by packaging and storage. The effect of the salt concentration in the brine has been a matter of controversy, with some indication that higher weight yield and quality may be obtained by using lower salt concentrations than by using a fully saturated brine solution. Therefore to test this hypothesis, the effect of different brine salting methods was studied; traditional brine salting, maintaining a constant brine concentration and increasing the salt concentration gradually during brining. The results indicated that the effect on weight yield, chemical composition and water holding capacity of the salted or rehydrated cod were not significant. Altering salt concentration of the brine, by adding salt during brining, did not result in any significant improvements in weight yield, either after the salting process or after the rehydration. The overall quality was increased by using a lower salt concentration of 16° Bau compared with 20 and 24° Bau.     

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.     

Influence of the hydrolysis process on the biological activities of protein hydrolysates from cod (Gadus morhua) muscle

Upgrading of fish protein through limited proteolysis of by‐products and surplus of the food industry generates peptides of interest to food formulation, the animal feed industry and aquaculture. The hydrolysis process has been studied in order to investigate the role of the limiting parameters. Hydrolysates obtained under varying conditions of temperature, pH, time and enzyme concentration were tested on fibroblastic cell cultures and in gastrin radioimmunoassays. Several fractions were shown to contain biologically active peptides such as growth factors or secretagogues (gastrin and cholecystokinin). Under optimum conditions we obtained 160% stimulation of cell growth with only 25 µg ml ⁻¹ hydrolysates, and about 0.25 pg gastrin‐like peptides mg⁻¹ sample. The process of hydrolysis plays a key factor by extending the time of protein degradation in generating these molecules. © 2000 Society of Chemical Industry     

Effects of calcium,magnesium and pH during salt curing of cod (Gadus morhua L)

The quality of heavily salted cod as influenced by adjusted levels of calcium, magnesium and pH in the salt was investigated. The investigation was carried out as a multivariate study consisting of two separate 2³ full factorial designs. Chemical composition, water‐holding capacity, weight and protein yields, colour and firmness were used as quality indicators or responses to the salt mixtures tested. The pH of the salt was positively correlated with the muscle pH of the cured fillet. The pH of the muscle correlated negatively with the relative protein content, lightness and sensory firmness of the cured muscle. Protein yield after salt curing was also negatively correlated with muscle pH. Calcium ions increased both the lightness and firmness and magnesium ions increased the lightness of the cured fillet. Copyright © 2004 Society of Chemical Industry     

Lipid and autoxidative changes in cold stored cod (Gadus morhua)

A study of lipid changes during the frozen storage of cod confirms that the major change is that of lipolysis. Oxidation is extremely slow and occurs primarily in the phospholipid fraction. Nevertheless, sufficient oxidation takes place during cold storage to reduce the acceptability of the fish primarily through the production of hept-cis-4-enal. The mechanism whereby hept-cis-4-enal occurs is discussed.     

Effect of season and fishing ground on the activity of lipases in byproducts from cod (Gadus morhua)

Lipase activity at acid and neutral pH has been measured in cut off, liver and viscera from cod caught in the Icelandic Sea (three different seasons) and the Barents Sea (one season). Lipase activity at pH 5 was highest in liver, while at pH 7 lipase activity was highest in viscera. Activity at pH 7 was higher than at pH 5 in liver and viscera, and at the same level in cut off. Lipase activity at pH 5 and 7 (20 °C) was higher in cut off samples from the Icelandic Sea in May–June, compared to October–December. Lipase activity at pH 7 (20 °C) was higher in cut off from the Barents Sea compared to the Icelandic Sea. No significant effect of season or fishing ground was found for liver lipase. Lipase activity at pH 5 and 7 in viscera from the Icelandic Sea was lower in May–June compared to the other seasons. Lipase activity was generally higher in viscera from the Icelandic Sea compared to the Barents Sea.     

Precursors of the volatile sulphides in spoiling north sea cod (Gadus morhua)

Quantitative analyses of the free sulphur amino acids, cyst(e)ine, methionine, taurine and glutathione in the muscle of spoiling chill-stored cod, showed that the concentrations of cyst(e)ine and methionine increased until the twelfth day of storage before decreasing rapidly. Only the disappearance of methionine and cyst(e)ine could be correlated with the production of volatile sulphides in the flesh. Taurine, the principal sulphur amino acid present appeared resistant to both microbial and autolytic enzymes, whilst glutathione disappeared before the onset of active bacterial spoilage. The importance of these compounds as odour and/or flavour precursors in white fish is dssed.     

Use of the voltammetric tongue in fresh cod (Gadus morhua) quality assessment

The aim of this work was to evaluate the use of the voltammetric tongue in the shelf-life assessment of fresh cod in cold storage. For this purpose, physico-chemical and microbial analyses were carried out, as well as measurements with the electronic tongue. The samples exceeded the acceptability limits of total volatile basic nitrogen (TVB-N), mesophilic and Enterobacteriaceae on the fourth day of storage, which means that the fish had a shelf-life of less than 4 days. The voltammetric tongue was able to differentiate between days 0 and 1 of storage from the other days. These results are in accordance with those obtained in the physico-chemical and microbial analyses, which showed a clear loss of freshness from day 0 to day 4. In the models obtained with partial least squares for TVB-N and mesophilic counts, the predicted values were successfully fitted to the experimental values, which confirm the potential usefulness of the voltammetric tongue for assessing cod spoilage.Industrial relevanceShelf-life assessment of fresh fish is of great interest for consumers, industries and authorities. The current methods used for this purpose are tedious, expensive, time-consuming and require skilled personnel. Therefore, the development of rapid non-destructive quality control techniques, which can be applied at any stage of the supply chain, could be highly interesting. This paper describes the possible application of a voltammetric tongue to assess cod spoilage during cold storage. This technique could be used as a rapid and non-destructive method applicable to routine quality control at any stage of the supply chain.     

Detection of nematodes in cod (Gadus morhua) fillets by imaging spectroscopy

ABSTRACT:  A promising method for detection of parasites in whitefish fillets has been developed. By use of imaging spectroscopy it is possible to record both spectral and spatial information from an object. In this work it is shown that by applying a white light transmission setup and imaging spectroscopy to cod ( Gadus morhua ) fillets, it is possible to make spectral images containing information to differentiate between fish muscle and parasites. The spectral images are analyzed by discriminant partial least square regression as well as image-filtering techniques. The method identifies parasites on the surface of the fillets as well as embedded parasites. One parasite was detected at 0.8 cm below the fillet surface, which is 2 to 3 mm deeper than what can be found by manual inspection of fish fillets. The method is nonintrusive and should thus be feasible for industrial purposes.     

The proteolytic activity of the crude enzyme extracts of Baltic cod (Gadus morhua) alimentary tract

The crude enzyme extract from Baltic cod alimentary tract had maximum activity of aspartic proteinases towards haemoglobin at pH 2.0 and 3.4, and of serine proteinases with casein as the substrate at pH 8.3 and 10.4. With bovine myofibrils as the substrate the proteolysis at pH 5.0-8.0 was maximum at the lowest and highest pH values. the optimum temperature for the proteolytic activity at pH 3.4 and 10.4 was 30–45°C and at pH 8.3 it was 40–50°C. Heating the crude extract for 10 min at pH 3.4,8.3, and 10.4 in the absence of the substrate had no effect on the activity of the acid and alkaline proteinases up to about 35–40°C. the stability at higher temperature decreased gradually and total inactivation occurred at 55–60°C. In the pH range 5.5–7.5 the proteolytic activity against bovine myofibrils was low at 0°C but brought about significant loss of myosin heavy chain at 20°C.     

The effects of presalting methods from injection to pickling, on the yields of heavily salted cod (Gadus morhua)

The production of heavy-salted cod (Bacalao) has changed from being a single-step process (kench) salting to a multistep procedure varying between producers and countries. Presalting by injection, brining, or pickling is increasingly applied prior to pile (dry) salting. This article describes the effects of different presalting methods (injection and brining, brining only, and pickling) on yield and chemical composition of salted cod fillets, in comparison to a single-kench salting step. The procedures used influenced the weight yields and chemical composition of the products. Injection was significantly different from other methods in increasing weight yields throughout brining, dry salting, and rehydration. The yield of nitrogenous compounds tended to be lower for injected and brine-salted fillets, mainly due to higher losses of nonprotein nitrogen. Practical Application: Salting procedures for cod have changed rapidly in recent years. Injection is increasingly used as a presalting method. It has been suggested to have strong effects on weight yields of salted cod products. This article describes the effects of injection on weight yields on products in salted, rehydrated, and cooked stage.     

Effect of pH on Sedimentation of Cod (Gadus morhua) Muscle Membranes

ABSTRACT: A new process solubilizes muscle proteins, making it possible to separate membranes with their oxidizable phospholipids, but it requires a high centrifugal force to separate the membranes. In this study we show that isolated cod muscle membranes could be readily sedimented at a low centrifugal g force for 15 min at pH 5 or below but not at pH 6 or higher. Isoelectric aggregation is likely to be responsible for the sedimentation of isolated membranes at these low pH values. Various consecutive pH treatments on isolated membranes showed that certain proteins were resolubilized or resuspended at a final pH of 10.5 if they had been previously exposed to pH 3,4, or 5. pH adjustment to 10.5 before adjustment to a pH of 5 or lower inhibited the sedimentation of isolated membranes. Isolated membranes added to the supernatant of homogenized muscle solubilized at pH 3 and centrifuged at 10000 × gfor 30 min also sedimented at 4000 × gfor 15 min. This was in contrast to the membranes naturally present in the solubilized homogenate. This suggests that factors other than viscosity were involved in the lack of efficient sedimentation of membranes from solubilized muscle tissue.     

Properties of actomyosin isolated from cod (Gadus morhua) after various periods of storage in ice

Natural actomyosin was isolated from cod (Gadus morhua L) stored in ice for up to 28 days. The gelling properties, apparent viscosity, Ca^2--ATPase activity and component protein composition by sodium dodecyl sulphate (SDS) electrophoresis were determined for each preparation of natural actomyosin. The apparent viscosity, protease activity, trimethylamine (TMA) content and pH of the fish muscle were also determined. The results showed that the apparent viscosity and Ca^2--ATPase activity tended to decrease slightly during ageing of the fish in ice, whereas some of the gelling properties showed a maximum between 3 and 6 days of storage. However, there was no change in the apparent viscosity of the muscle as a whole even after the fish were considered to be stale according to the TMA values. The ratio of myosin heavy chain to actin in the actomyosin changed with the time of storage of the fish, being highest at 3 days when gelling properties were maximal and decreasing progressively thereafter.     

Synthesis and degradation of adenosine triphosphate in cod (Gadus morhua) at subzero temperatures

This study has demonstrated that the extraction step is very important when analysing ATP and its degradation products. An important factor is whether the sample is fresh, frozen or thawed when homogenised since thawing of the sample will lead to rapid loss of ATP. During frozen storage it was found that ATP in cod (Gadus morhua) was stable at −40 °C in small samples for at least 12 weeks. At −20 °C it was found that ATP content increases initially and thereafter falls. It was demonstrated that degradation of ATP in small samples occurs faster at 0 °C than at −2 and −5 °C. Furthermore, it was found that in whole cod ATP could be synthesised at a significant rate at −7 °C. © 1999 Society of Chemical Industry     

Prediction,molecular docking and identification of novel umami hexapeptides derived from Atlantic cod (Gadus morhua)

This paper investigated umami hexapeptides derived from myosin of Atlantic cod (Gadus morhua) using homology modelling, molecular docking, taste evaluation and e-tongue verification. After hydrolysing and prediction in silico, potential bioactivity, toxicity and physicochemical properties of 48 hexapeptides were predicted. Five hexapeptides were selected to dock with the T1R1–T1R3 homology model which was built with SWISS-MODEL. Docking results showed that the five hexapeptides could enter the docking region, and INKPGL, SDSCIR and GPDPER had the lowest CDOKER_ENERGY. E-tongue result showed that the umami and richness value of all the three hexapeptides in 0.4 mg mL⁻¹ were higher than a 0.1% MSG solution. Sensory evaluation result showed that INKPEL had the strongest umami taste among the three hexapeptides and the umami threshold value was 0.25 mg mL⁻¹. These results suggested that homology modelling can be used for predicting umami peptides, and three umami hexapeptides were identified by in silico screening.     

Gelatinolytic activities in muscle of Atlantic cod (Gadus morhua), spotted wolffish (Anarhichas minor) and Atlantic salmon (Salmo salar)

The gelatinolytic activity in muscle from Atlantic cod (Gadus morhua), spotted wolffish (Anarhichas minor) and Atlantic salmon (Salmo salar) was studied using gelatin SDS‐PAGE, gelatin affinity chromatography and enzyme inhibitors. These fish species are known to differ markedly in fillet softening and gaping post mortem. Atlantic cod, which is a promising species for cold water marine aquaculture, often shows such negative properties, particularly after being well fed. Gelatinolytic activity bands were present in all three species. Using gelatin chromatography and enzyme inhibitors, both serine proteinases and metalloproteinases were detected in wolffish and cod muscle, while only the latter were found in salmon muscle. Activation of the metalloproteinases by p‐aminophenylmercuric acetate (APMA) resulted in a shift in activity from higher to lower molecular weight, as is known for mammalian matrix metalloproteinases. In all three species the molecular weight of the metalloproteinases was lowered from approximately 80 to about 70 kDa by activating with APMA. Copyright © 2003 Society of Chemical Industry