1H and 23Na MRI studies of Atlantic salmon (Salmo salar) and Atlantic cod (Gadus morhua) fillet pieces salted in different brine concentrations

BACKGROUND: Applicability of magnetic resonance imaging (MRI) to quantitative analysis of sodium in salted fish products is usually impaired by the partial ²³Na MRI ‘invisibility’ phenomena as well as high investment costs of the MRI equipment. RESULTS: Salmon and cod fillet pieces, unsalted and brine salted (50, 100, 150, 200 and 250 g kg^?1 NaCl) for 48 h, were studied using ¹H and ²³Na MRI. Based on MRI results, T₁ and T₂ relaxation times were calculated for ¹H and the T₂ time for ²³Na nuclei. In addition, water diffusion images for all fillet samples and reference brine solutions were obtained. Variation of the nuclear magnetic resonance relaxation times and water diffusion constants with brine concentration is discussed in terms of the muscle structural changes. Sodium MRI visibility factors for the MRI method used were determined for all fish samples. CONCLUSION: Observed changes in proton and sodium NMR relaxation times with the salt content reflect complex counteraction of several factors related to the muscle structural changes. Sodium MRI visibility factors appear to be dependent on a number of experimental factors in a complex matter, making quantitative sodium analysis by the MRI technique used non‐trivial. Copyright © 2007 Society of Chemical Industry     

Quality changes during refrigerated storage of MA-packaged pre-rigor fillets of farmed Atlantic cod (Gadus morhua L.) using traditional MAP, CO2 emitter, and vacuum

ABSTRACT:  Quality changes during 3 wk of refrigerated storage (1.3 °C) were studied on pre -rigor filleted farmed Atlantic cod packed in modified atmosphere (MAP, 60% CO₂ and 40% O₂) or vacuum. The packages of MAP contained either a CO₂ emitter and low gas volume to product volume (g/p ratio) of 1.3, or a 3.9 g/p ratio and no emitter. The CO₂ level remained stable or increased in the packages with CO₂ emitter, whereas the CO₂ level in the packages with no CO₂ emitter decreased to 40% after 4 d of refrigerated storage. High levels of oxygen in the gas mixture prevented formation of trimethyl amine (TMA) during storage of the MA-packed fish, whereas the TMA content increased significantly after 10-d storage in vacuum. MA-packed samples had the highest values of 1-penten-3-ol. Sensory scores of sour, sulfur, and pungent odors were significantly higher for vacuum-packed cod compared to the 2 MA-packaging methods measured 14 d after slaughtering. No differences in sensory scores were observed between the 2 methods of MAP, and shelf life of these samples seemed to be 14 to 21 d. Cod samples packaged in vacuum packages had higher pH values compared to ordinary MAP and packages containing a CO₂ emitter. Bacterial growth was inhibited by MAP and resulted at the end of the storage period in dominance of Carnobacterium and some Photobacterium . In MA packages with high O₂ levels the Photobacterium was inhibited. It is concluded that CO₂ emitters are well suited for reduction of transport volume for MA-packaged farmed cod.     

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.     

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.     

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.     

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     

Salting and Desalting of Fresh and Frozen-thawed Cod (Gadus morhua) Fillets: A Comparative Study Using 23Na NMR, 23Na MRI, Low-field 1H NMR, and Physicochemical Analytical Methods

ABSTRACT: Fresh and frozen-thawed cod raw materials were subjected to brining, dry salting, and rehydration. The effects of salting and desalting on fillet water-related properties, salt content, and salt distribution were studied using 23Na MRI, 23Na NMR, and low-field (LF) 1H NMR. The results were compared with the Volhard titration method for salt determination, fillet pH, water content, and water-holding capacity. The rehydrated end product showed significant difference only with respect to water-holding capacity (unfrozen raw material higher) when fresh and frozen-thawed raw materials were compared. Excellent correlation was obtained between quantitative salt determinations using 23Na NMR and Volhard titration. When using a typical salting method, it was shown that the salt uptake and salt distribution in the fillets were inhomogeneous. Proton relaxation times, obtained from LF 1H NMR, were processed using either a 2-exponential model or the CONTIN algorithm. In several instances, a clear dependence on fillet pH, water-holding capacity, or salt content during fish processing was observed. Our results indicate that NMR and MRI can be used as useful tools to evaluate and optimize fish processing unit operations and that rapid (LF) NMR methods have the potential for replacing traditional salt and water-related analytical methods.     

A comparative study of quality and safety of Atlantic cod (Gadus morhua) fillets during cold storage,as affected by different thawing methods of pre‐rigor frozen headed and gutted fish

BACKGROUND

The catch of marine whitefish is typically seasonal, whereas the land‐based processing industry has a need for all‐year stable supply of raw materials. This challenge can be met by applying fish frozen at sea. When using frozen fish, the methods employed for thawing may influence the safety and quality of the final product. This study aimed to investigate the applicability of novel thawing strategies in order to provide an all‐year supply of high‐quality and safe cod products.

RESULTS

Comparative investigations of quality and safety factors after thawing in water, with and without air circulation, and contact thawing were performed. The parameters included water‐holding capacity, thawing loss, drip loss, cooking yield, sensory evaluation and microbiological analyses (including total volatile bases nitrogen). Water thawing with air circulation provided faster thawing than water thawing without air circulation and contact thawing. For all three methods, the quality of the thawed fish was acceptable and the shelf life of the fillets during chilled storage was between 10 and 14 days post‐filleting.

CONCLUSION

The results show that controlled freezing of cod, followed by appropriate thawing, may provide the processing industry with an all‐year delivery of raw materials, without compromising quality and safety of the final product. © 2017 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of 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     

Effects of different cooking methods on the mineral contents of wild and farmed sea bream (Sparus aurata)

The effects of different cooking methods (steaming, boiling, oven cooking, grilling, frying in olive oil, frying in soybean oil, frying in corn oil and frying in sunflower oil) on mineral contents (Ca, Mg, K, Na, Fe, Zn, Cu and Mn) of wild and farmed sea bream (Sparus aurata) were determined. The moisture rate decreased significantly (P < 0.05) after boiling, grilling, oven cooking and frying but remains stable after steaming. The fat content increased with different frying treatments. The Ca, Mg, Na, K and Zn contents of wild and farmed sea bream cooked by almost all methods significantly decreased (P < 0.05). The Cu content in grilled wild and farmed sea bream increased significantly (P < 0.05). Losses of mineral content in fried sea bream were higher than those of fish cooked by other methods. On comparing the raw and cooked fish, the results indicated that cooking had considerable effect on the mineral contents.     

Characterisation of the bacterial flora of modified atmosphere packaged farmed Atlantic cod (Gadus morhua) by PCR-DGGE of conserved 16S rRNA gene regions

The present article describes the use of broad-range molecular analyses to characterise the microbial population of farmed Atlantic cod (Gadus morhua) packaged for the retail market. Cod was filleted post rigor, packaged in air or in modified atmosphere (MA) (50% CO(2):50% N(2) or 50% CO(2):50% O(2)) and stored at 0 degrees C for 11 days. To determine the community profiles of the samples the variable V3-region of the bacterial 16S rRNA gene were amplified by PCR, before the PCR products were separated by denaturing gradient gel electrophoresis (DGGE). From sequence analyses Pseudomonas spp. were found to be the predominant bacteria in oxygen enriched atmospheres, whereas the spoilage bacteria Photobacterium sp., Shewanella putrefaciens and Pseudomonas spp. dominated in CO(2):N(2) and air packaged samples. Additional microbial analyses by cultivation methods observed highest bacterial numbers in air stored samples, and both MA mixtures gave growth inhibition when measuring aerobic plate count, psychrotrophic bacteria and H(2)S-producing bacteria. The results show that PCR-DGGE can be applied to examine bacterial diversity and population shifts among different MA-packaged products.     

Water-holding capacity of wild and farmed cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) muscle during ice storage

The aim of this study was to investigate how the presence of normal spoilage bacteria influenced the water-holding capacity (WHC) of wild cod, farmed cod and haddock during chilled storage. Bacterial growth was inhibited by soaking the fillets in 3 mmol/l NaN₃ prior to storage. The results clearly showed that the three groups were different with respect to WHC and pH. Muscle pH was highest in haddock, lower in wild cod and lowest in the farmed cod. Significant differences in WHC between the NaN₃-treated and nontreated groups of wild cod and haddock were found on the last sampling day. However, there was an inconsistency with respect to the relationship between pH and percentage liquid loss (LL%). The microflora of farmed cod is obviously altered from what is normal for wild cod. The results showed that bacterial growth may influence the WHC of the muscle. However, the relationship is inconsistent and may be temporal and not causative.     

Changes in myofibrillar proteins during processing of salted cod (Gadus morhua) as determined by electrophoresis and differential scanning calorimetry

The effects of salt-curing, drying and rehydration on muscle proteins in cod (Gadus morhua) were studied during the processing of heavily salted cod or “bacalhau”. The aim was to observe conformational stability and possible degradation or denaturation, with sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and differential scanning calorimetry (DSC). The salting process significantly decreased the heat stabilities of both myosin and actin. The decrease in water content during dry-salting did shift the transition temperatures slightly back to higher temperatures. The results, from the SDS-PAGE, showed that the myosin heavy chain (MHC) was cleaved into smaller sub fragments in the salting process with the two heavy meromyosin fractions (HMM S1 and S2) and the light meromyosin (LLM) fraction being the most abundant. Actin was less affected than myosin.     

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     

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.