Automatic nematode detection in cod fillets (Gadus morhua) by transillumination hyperspectral imaging

Traditional quality control of cod fillets is currently made by manual inspection on candling tables. This is a time consuming and expensive operation, contributing to a significant share of the cost with cod fillet production. In this study, transillumination hyperspectral imaging was implemented as a method for automatic nematode detection in cod fillets moving on a conveyer belt, and evaluated on industrially processed cod fillets. An overall detection rate of 58% of all nematodes (N= 922), with detection rate of 71% and 46% for dark and pale nematodes, respectively, is reported. This is comparable, or better, than what is reported for manual inspection under industrial conditions. The false alarm rate was high, with 60% of the fillets reported with one or more false alarms. These results show that the method is promising, but needs further refinements to reduce the false alarm rate and increase the imaging speed from 25 to 400 mm/s. Practical Application: Manual inspection of cod fillets is a huge bottleneck for the industry, accounting for half the production cost with cod fillet processing and reducing the processing speed. Transillumination hyperspectral imaging has the potential to reduce the manual labor required for cod fillet inspection and hence reduce the cost and increase the end product quality.     

A comparison of biochemical changes in cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) fillets during frozen storage

Changes in the muscle proteins of frozen cod fillets, which produce significant amounts of formaldehyde, and frozen haddock fillets, which produce negligible formaldehyde, were compared. Protein extractability and hydrophobicity and the amino acid contents of soluble and insoluble proteins, as well as formaldehyde formation, were investigated in matching pairs of cod and haddock fillets stored at ?10 and ?30 °C (control). Formaldehyde production in cod was much higher (845 and 1065 nmol g^?1 at 20 and 30 weeks respectively) than in haddock (93 and 101 nmol g^?1 after 20 and 30 weeks respectively) at ?10 °C. However, a rapid decrease in solubility of proteins, increase in hydrophobicity and decrease in the amino acid content of salt‐soluble proteins at ?10 compared with ?30 °C were observed in both species. The results showed that there were no significant differences in the nature of the protein changes between these two species, thus indicating that factors other than formaldehyde were involved in the denaturation of proteins and the formation of aggregates during frozen storage of cod and haddock fillets, especially at ?10 °C. © 2001 Society of Chemical Industry     

Automatic nematode detection in cod fillets (Gadus morhua L.) by hyperspectral imaging

Detection of objects embedded in tissue, using visible light, is difficult due to light scattering. The optical properties of the surrounding tissue will influence the spectral characteristics of the light interacting with the object, and the spectral signature observed from the object will be directly affected. A method for calibrating the spectral signature of small objects, embedded in translucent material, by the estimated local background spectrum is presented. The method is evaluated under industrial conditions in a new hyperspectral imaging system for automatic detection of nematodes in cod fillets. The system operates at a conveyor belt speed of 400 mm/s which meets the industrial required speed of assessing one fillet per second. The local calibration method reduces the number of spectra needed to be classified by 89.6%. For one or more false alarms in 60% of the fillets sampled after the trimming station, the Gaussian maximum likelihood classifier detects 70.8% and 60.3% of the dark and pale nematodes, respectively. This is better than what is previously reported using a higher resolution instrument on a slow moving conveyor belt, and comparable or better to what is reported for manual inspection under industrial conditions.     

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     

Automatic freshness assessment of cod (Gadus morhua) fillets by Vis/Nir spectroscopy

VIS/NIR spectroscopy for differentiating between fresh and frozen-thawed cod fillets and for assessing the freshness as days on ice has been evaluated. Both a handheld interactance probe for doing quick measurements of single fillets and an imaging spectrometer for doing online analysis at industrial speed of one fillet per second, have been used. Results show that frozen-thawed cod fillets can be fully separated from fresh fillets using a small subset of wavelengths in the visible region. Freshness as days on ice can be determined with an accuracy of 1.6 days on individual fillets. The results indicate that oxidation of hemoglobin and myoglobin during freezing-thawing and cold storage on ice are explaining most of the variations seen in the visible region of the spectrum.     

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.     

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.     

Perfluoroalkyl substances (PFAS) in beaked redfish (Sebastes mentella) and cod (Gadus morhua) from arctic fishing grounds of Svalbard

ABSTRACT

The present study gives an overview about the concentration of PFAS in liver, fillet and belly flap of beaked redfish (Sebastes mentella) and cod (Gadus morhua) caught in pristine arctic fishing grounds of Svalbard. Out of 17 analysed substances, only six perfluoroalkyl acids (PFAAs) could be detected in the fish. The most frequently quantified substances were PFOS and perfluoroundecanoic acid (PFUnA) in liver (100%) and fillet (at least 40% and 70%, respectively) of beaked redfish and cod, and in belly flap of beaked redfish (100%). Compared to cod, beaked redfish showed significant higher PFAA concentrations with highest levels in liver. Multiple comparisons of group differences for PFAA concentrations among fish species and matrices were independent of the evaluation method, but not for the PFAA-pattern analysis. The risk assessment of PFOS indicated that beaked redfish and cod caught in the Barents Sea can be a relevant exposure source for consumers.     

Influence of storage time and temperature on lipid deterioration during cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) frozen storage

Lean fish deterioration during frozen storage (−30 and −10 °C) for up to 1 year was studied by the assessment of lipid changes. Comparison between a formaldehyde (FA)-forming species (cod) and a non-FA-forming one (haddock) was carried out. Lipid damages were measured on the basis of free fatty acids (FFA), peroxide value (PV), thiobarbituric acid index (TBA-i) and fluorescent compounds. In both species at −30 °C, most lipid damage indices showed significant correlations with the storage time. However, at −10 °C, only the FFA and fluorescence detections provided significant correlations with the storage time. Comparison between the fish species showed higher lipid oxidation (PV and TBA-i) and hydrolysis (FFA content) in haddock than in cod at −10 °C; however, a higher fluorescence development was observed in cod at the same temperature. At −30 °C, little differences in lipid damage indices were detected between the two species. © 1999 Society of Chemical Industry     

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.     

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     

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     

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.     

Microbial and sensory changes during refrigerated storage of desalted cod (Gadus morhua) preserved by combined methods

Water blanching and the use of additives (potassium sorbate and citric acid) combined with different types of packaging (air, vacuum "VP" and modified atmosphere packaging "MAP": 60% CO(2), 30% N(2) and 10% O(2)), were studied as new methods of preservation of chilled desalted cod. Microbial counts and total volatile basic nitrogen (TVB-N) analyses were carried out during a period of 42 days on all samples stored at 4 degrees C. No Aeromonas or sulphite-reducing Clostridium were isolated from any of the analysed samples. The lowest microbial counts of mesophilic, psychrotrophic, Pseudomonas, moulds and yeasts, were found in samples with additives in all kinds of packaging. These samples in VP or MAP maintained an excellent microbial quality throughout the 42 days of storage, with mesophilic and psychrotrophic counts always below 4 log CFU/g. Counts of the four microorganisms above-mentioned in blanched samples packaged with air, exceeded 5 log CFU/g on days 21-28, so it became necessary to use VP or MAP to maintain these microorganisms at an acceptable level for the entire storage period. TVB-N contents were low in samples with additives, regardless of the kind of packaging, as well as in blanched samples packaged in VP and MAP, never reaching 25 mg/100 g. Since there were no significant differences either in microbial growth or in TVB-N between samples in VP and MAP, a sensory analysis was performed only in desalted cod submitted to the two treatments (blanching and additives) combined with VP, both in raw and cooked samples. The results of this analysis showed that the addition of potassium sorbate and citric acid did not alter the typical organoleptic features of desalted cod. The sensory characteristics of both blanched samples and those with additives in VP showed no change during the period of the study.     

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.     

Collagenase activity and protein hydrolysis as related to spoilage of iced cod (Gadus morhua)

Collagenase activity and changes in muscular protein of iced Atlantic cod stored for 9 days were studied. The crude fish muscle extract showed maximum collagenase-like activity against bovine insoluble tendon collagen at 48 h of incubation at 37 °C. Collagenase activity against synthetic substrate increased (P<0.05), especially for fish in initial and advanced stages of decomposition. These results suggest that endogenous collagenases and other proteases may be responsible for the destruction of fine collagenous fibrils in the skeletal muscle of cod. The content of titin 1 decreased when decomposition was advanced. Moreover, a progressive degradation of sarcoplasmic proteins with a molecular weight of 100, 94, 85 and 80 kDa was observed. Results suggest that softening of cod muscle during iced storage is caused more by collagenase activity than by proteolysis of myofibrils.