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.     

Low salt brining of pre-rigor filleted farmed cod (Gadus morhua L.) and the effects on different quality parameters

Pre-rigor processing of cod fillets may have economic benefits, but this potential has usually been overshadowed by process-linked difficulties such as pin bone removal, rapid rigor onset and higher drip losses. The aim of this work was to study the impact on fillet quality parameters after immersing pre-rigor filleted farmed cod in different NaCl solutions ranging from 15 to 60 g/L. Temperature of the fish at death was 4 °C, in immersion solutions 2 °C, and following immersion the fillets were stored in ice within plastic bags for 14 days. As controls, one group was filleted pre-rigor but not immersed, and one group was filleted post-rigor and not immersed. Immersing in salt solution resulted in better yield compared to both control groups. Higher salt content generally increased rigor contraction, but significantly reduced fillet gaping and the force required to pull pin bones. Thus, relatively low salt levels within the fillets had a positive impact on some of the problems associated with pre-rigor filleting.     

Effects of pre-slaughter stress on proteolytic enzyme activities and muscle quality of farmed Atlantic cod (Gadus morhua)

Farmed Atlantic cod were subjected to a combination of stressors in a holding tank before being killed, pre rigor filleted and stored in ice. At slaughter, a higher level of stress was confirmed by blood physiology analyses. This was further associated with significantly reduced muscle pH and somewhat elevated muscle collagenase-like activity in the stressed fish, whereas no differences in cathepsin-like activities were found. After 5 days of iced storage, the stressed fish had significantly lower water holding capacity, reduced hardness and yellowish colour compared to the control group, and no differences in the other parameters investigated. Independent of pre-slaughter stress, the activities of cathepsin B- and B/L-like enzymes increased and activities of cathepsin D/E- and collagenase-like enzymes decreased with storage.     

The optimized modified atmosphere for packaging of pre-rigor filleted farmed cod (Gadus morhua) is 63 ml/100 ml oxygen and 37 ml/100 ml carbon dioxide

The optimal initial gas composition to maintain quality of modified atmosphere (MA) packaged pre-rigor filleted farmed Atlantic cod (Gadus morhua) at 0 °C was determined through sensory evaluation of raw odour and chemical, physical, and microbiological analyses. Cod packaged under gas to product ratio of 2:1 and gas mixtures according to a simplex centroid mixture design spanning the whole area from 0 to 100 ml/100 ml and in between mixes of all the three major packaging gases, CO₂, O₂ and N₂ were analysed after 7, 10 and 14 days of storage. Aerobic and psychrotrophic plate count decreased and formation of exudates increased with increasing CO₂ concentration. H₂S-producing bacteria were not present or not able to grow under the different gas mixtures. Odour scores and trimethylamine oxide content decreased and the formation of trimethylamine increased in the fish with decreasing CO₂ and O₂ levels. The weighted optimum gas mixture for MA packaging of farmed cod was determined to be 63 ml/100 ml O₂ and 37 ml/100 ml CO₂.     

The influence of different acids and pepsin on the extractability of collagen from the skin of Baltic cod (Gadus morhua)

Solutions of (0.5 M) citric, lactic and acetic acids and 0.15 M HCl were used for the extraction of collagen from the whole skins of Baltic cod (Gadus morhua). The extractions were performed at a temperature of 4 °C for 24, 48 and 72 h using a solid/solution ratio of 1:6 (w/v). Of the acids used, HCl was the least effective solvent for collagen. The maximal yield of collagen extracted with citric acid was 60%. Collagen extraction with acetic or lactic acid give a maximal yield of about 90% with HCl yielding of only 18%. After enzymatic treatment of cod skin the yield of protein extracted with HCl and citric acids increased to 40% and 20%, respectively. Collagen was completely solubilized under the same conditions in acetic and lactic acids. Electrophoretic analysis of collagens extracted in HCl and citric acids with enzymatic treatment proved that the isolated protein was denaturated. The solutions of acetic and lactic acids are solvents for native collagen.     

Influences of potassium ferrocyanide on lipid oxidation of salted cod (Gadus morhua) during processing, storage and rehydration

The effects of added potassium ferrocyanide (CN) in different concentrations (2.5 ppm, 7.5 ppm and 100 ppm), in salt, on lipid oxidation in cod during salting, storage and rehydration were examined in this study. An increase in CN concentration accelerated lipid oxidation of the salted cod, as observed by increases in lipid hydroperoxides (PV) and thiobarbituric acid-reactive substances (TBARS), as well as in the development of fluorescence compounds (δF_or and δF_aq). A yellow discolouration (higher b^∗ value) of salted cod was associated with higher levels of oxidation derivatives. High correlation between PV, TBARS and free fatty acid (FFA), as well as between FFA and δF_or, was found. The results of principal component analysis showed that TBARS, b^∗ value and δF_or were the strongest indicators of lipid oxidation during salting and storage.     

Purification and characteristics of trypsins from cold-zone fish,Pacific cod (Gadus macrocephalus) and saffron cod (Eleginus gracilis)

Trypsins from the pyloric ceca of Pacific cod (Gadus macrocephalus) (GM-T) and saffron cod (Eleginus gracilis) (EG-T) were purified by gel filtration on Sephacryl S-200 and Sephadex G-50. The final enzyme preparations were nearly homogeneous on SDS–PAGE and the molecular weights of both enzymes were estimated to be approximately 24 kDa by SDS–PAGE. The specific trypsin inhibitors, soybean trypsin inhibitor and TLCK, strongly inhibited the activities of GM-T and EG-T. The optimum pH and optimum temperature of both trypsins were around pH 8.0 and 50 °C, respectively, using N^α-p-tosyl-l-arginine methyl ester as substrate. The GM-T and EG-T were unstable above 30 °C and below pH 5.0, and they were stabilised by calcium ion. The N-terminal amino acid sequences of GM-T (IVGGYECTRHSQAHQVSLNS) and EG-T (IVGGYECPRHSQAHQVSLNS) were found. The percentage of hydrophobic amino acid in the N-terminal 20 amino acids sequences of these cold-zone fish trypsins was lower (28%) than those of temperate-zone fish trypsins (34%), tropical-zone fish trypsins (37%) and mammalian trypsins (34%). Whereas the content of charged amino acids in the GM-T and EG-T was relatively higher than those of trypsins from temperate-zone fish, tropical-zone fish and mammals. Moreover, the GM-T catalyzed synthesis of N^α-(tert-butoxycarbonyl)-l-alanyl-l-alanine-p-nitroanilide (N^α-Boc-l-Ala-l-Ala-pNA) has been studied by using N^α-(tert-butoxycarbonyl)-l-alanine-p-guanidinophenyl ester [N^α-Boc-l-Ala-OpGu (inverse substrate)] as acyl donor and l-alanine-p-nitroanilide (l-Ala-pNA) as acyl acceptor, respectively.     

Breakdown of intramuscular connective tissue in cod (Gadus morhua L.) and spotted wolffish (Anarhichas minor O.) related to gaping

The purpose of this work was to compare the microstructure of muscle connective tissue in cod and wolffish and to study its degradation during ice-storage to determine which structural alterations are related to the gaping phenomenon. Gaping is very often found in fillets of codfish, but not in wolffish. The results showed that detachments between myofibres occurred prior to the myotomes to myocommata detachments, which occurred more rapidly and to a larger extent in cod than in wolffish. Changes at the ultrastructural level in myocommata proper were mainly related to gaps between collagen fibres and between collagen fibres and cells in the extracellular matrix (ECM). The mean collagen fibre diameter was smaller and the collagen network in myocommata proper was denser in wolffish than in cod. After 7 days of ice-storage the collagen fibres, particular in cod, appeared sparsely packed. The results implied that the increased gaping during ice-storage might be due to degradation of proteoglycans and glycoproteins, important for the spatial organization of the collagen fibres and in anchoring cells in the ECM to the collagen network.     

Isolation and some properties of collagen from the backbone of Baltic cod (Gadus morhua)

Ossein from Baltic cod backbone was obtained after extraction of non-collagenous protein with 0.1 M NaOH solution and demineralization with 1.0 M HCl solution. The extractions were performed at 4 °C for 24, 48 and 72 h using a solid/solution ratio from 1:4 to 1:8 (w/v). After 48 h of extraction in 0.5 M acetic acid only about 25% of collagen was dissolved. After 48 h of extraction at optimal concentration of pepsin (4 mg/g ossein) the collagen was dissolved almost completely. Collagen solubilized in acetic acid could be almost completely precipitated with κ-carrageenan, at protein/polysaccharide ratio 1:1 (w:w). The denaturation temperature of Baltic cod backbone collagen was 14.4 °C and the conversion factor of hydroxyproline to collagen was 15.7.     

Acid-induced gelation of natural actomyosin from Atlantic cod (Gadus morhua) and burbot (Lota lota)

The acid-induced gelation of natural actomyosin (NAM) from burbot (Lota lota) and Atlantic cod (Gardus morhua) added with d-gluconic acid-δ-lactone (GDL) during incubation at room temperature (22–23 °C) for 48 h was investigated. During acidification, pH values of both NAMs reached 4.6 within 48 h. Both NAMs underwent aggregation during acidification as evidenced by increases in turbidity and particle size, especially after 6 h of incubation. The decreases in Ca²⁺-ATPase activity and salt solubility of both NAMs were observed during incubation. Decreases in total sulphydryl content with the concomitant increases in disulphide bond content of NAM from both species were also noticeable. Additionally, surface hydrophobicity of NAM increased, suggesting the conformational changes in NAM induced by acidification. The storage modulus (G′) values increased with increasing incubation time and G′ development was greater in Atlantic cod NAM, compared with burbot NAM. Differential scanning calorimetry (DSC) revealed that T_max and enthalpy of myosin peak shifted to the lower values and endothermic peak of actin completely disappeared. In general, gel development was more pronounced in Atlantic cod NAM, compared with the burbot counterpart. As visualised by transmission electron microscopy, network strands of aggregates from Atlantic cod were finer and more uniform than those of the burbot counterpart. Acid-induced gelation of NAM from both fish species therefore involved both denaturation and aggregation processes. However, gelation varied with fish species and had an impact on the resulting gels.     

Comparative study on acid-induced gelation of myosin from Atlantic cod (Gardus morhua) and burbot (Lota lota)

Physicochemical and rheological properties of myosin from Atlantic cod and burbot during acid-induced gelation at room temperature (22–23 °C) by d-gluconic acid-δ-lactone (GDL) were monitored. Turbidity and particle size of both myosins increased and salt soluble content decreased when pH decreased, suggesting the formation of protein aggregates caused by acidification. The formation of disulphide bonds in myosin gelation was induced by acid. Ca²⁺-ATPase activity of myosin decreased (p < 0.05), while surface hydrophobicity increased during acidification (p < 0.05). Furthermore, the decreases in maximum transition temperature (T_max) and the denaturation enthalpies (ΔH) were found in both myosins. During acidification, the increases in storage modulus (G′) and loss modulus (G″) of myosin were observed (p < 0.05), revealing the formation of elastic gel matrix. Thus, gelation of myosin from Atlantic cod and burbot could take place under acidic pH via denaturation and aggregation. However, myosin from Atlantic cod was generally more favourable to gelation than was burbot myosin.     

Headspace volatile components of smoked swordfish (Xiphias gladius) and cod (Gadus morhua) detected by means of solid phase microextraction and gas chromatography–mass spectrometry

A study of the headspace of smoked swordfish and cod was carried out by means of Solid Phase Microextraction followed by gas chromatography–mass spectrometry. The headspace of both smoked fish species contains ketones, aldehydes, alcohols, acids, esters, hydrocarbons, ethers, nitrogen derivatives, phenol, guaiacol, and syringol derivatives, as well as some chlorinated contaminants. The differences found between the headspace of both smoked fish are basically due both to a higher proportion of smoke components in cod than in swordfish, and to specific fish components being present or absent in each fish sample. The high proportion of syringol in both fish samples indicates that smoking was carried out using hardwood. Some smoke components were not detected in the headspace of these smoked fish samples.     

Effect of processing on amine formation and the lipid profile of cod (Gadus morhua) roe

The processing of fish roe leads to changes in its chemical composition, the extent of which depends on the techniques and additives employed. This study aimed to investigate the effects of ripening temperature and the use of sodium benzoate and citric acid on the quality of ripened cod roe, with respect to the contents of volatile base nitrogen (VBN), trimethylamine (TMA), biogenic amines (BA) and on the lipid composition. In comparison with fresh roes, ripened roes presented higher contents of VBN, TMA, BA and the proportion of free fatty acids regardless of the temperature and additives used during the ripening process. The greatest increases were observed in the samples ripened at 17 °C without additives, in which histamine was detected at 8.8 mg/100 g. A low ripening temperature was the main factor responsible for minimising changes in the cod roe composition. The addition of sodium benzoate as a preservative or citric acid to decrease the pH value had a significant effect in maintaining the quality of the cod roes, mainly at high ripening temperature.     

The effects of salt-curing and salting procedures on the microstructure of cod (Gadus morhua) muscle

The aim of this study was to investigate the effects of salting and different pre-salting procedures (injection and brining versus brining only) on the microstructure and water retention of heavy salted cod products. Salting resulted in shrinkage of fibre diameter and enlargement of inter-cellular space. Water was expelled from the muscle and a higher fraction became located in the extra-cellular matrix. These changes were suggested to originate from myofibrillar protein aggregation and enzymatic degradation of the connective tissue. During rehydration, the muscle absorbed water again and the fibers swelled up to a similar cross-sectional area as in the raw muscle. However, the inter-cellular space remained larger, resulting in a higher water content of the muscle in the rehydrated stage. The effects of different salting procedures were strongest after salting. At that stage of the process, the inter-cellular space tended to be larger in the injected and brined muscle than in the brined only.     

Characterisation of high added value compounds in wastewater throughout the salting process of codfish (Gadus morhua)

In Portugal Atlantic codfish (Gadus morhua) is dry-salted with food-grade marine salt for 6 days. During this process, codfish incorporates salt and drains away water up to 22%(w/w) of its weight, which contains important compounds, such as free amino acids, peptides and proteins. Hence, the chemical profile of such water, composed of various soluble nitrogen fractions, was thoroughly determined.     

Low field Nuclear Magnetic Resonance on the effect of salt and modified atmosphere packaging on cod (Gadus morhua) during superchilled storage

Low field Nuclear Magnetic Resonance was used to evaluate the effect of salt and modified atmosphere packaging (MAP) on cod loins during superchilled storage. Transversal and longitudinal proton relaxation times of the cod loins were measured with Carr-Purcell-Meiboom-Gill (CPMG) and Inversion Recovery (IR) pulse sequences respectively. The relaxation parameters reflected the observed differences in the muscle caused by variation in salt concentration, the choice of salting method (brining or brine injection) and packaging (air or MAP), as well as superchilled storage temperature and storage time. Significant correlations were found between the NMR parameters and parameters describing the water dynamics of the muscle (moisture and salt content, water holding capacity, drip and cooking yield), as well as muscle pH and counts of H₂S-producing bacteria in chosen sample groups. The study showed the possibility of using low field NMR to indicate fish quality deterioration, when the spoilage mechanisms affect the water properties and muscle structure.     

Biochemical,sensory and microbiological attributes of wild turbot (Scophthalmus maximus), from the Black Sea,during chilled storage

Freshness of wild turbot (Scophtalmus maximus) stored in ice was assessed by chemical, sensory and microbiological methods. The limit for sensory acceptability of wild turbot stored in ice was ∼12–15 days. The quality of turbot decreased on day 15 (B) and they were no longer acceptable on day 19 (C). The TVB-N level showed fluctuations during storage, indicating that TVB-N could not be a good indicator of turbot quality. The release of FFA increased from an initial value of 6.33 (expressed as % of oleic acid) to a final value of 20.6 during the storage period. The initial PV value was 5.60 meq/kg for turbot stored in ice and it started to increase to 21.6 meq/kg on day 12 and then started to decrease to 13.6 meq/kg at the end of storage period. The level of TMA in wild turbot increased sharply from an initial value of 9.36 mg/kg to a final value of 38.9 mg/kg. Linear regressions (r²) obtained from K, K_i, G, P, H and F_r were 0.92, 0.89, 0.99, 0.89, 0.96 and 0.89, respectively, for the wild turbot stored in ice. Turbot maintained high (E) and good quality (A) during the first 12 days of chilled storage when the average K, K_i and P values were ∼78–85%, and H, F_r and G values were ∼45%, 15% and 149%, respectively. Eight biogenic amines were investigated, namely, histamine, putrescine, cadaverine, spermidine, spermine, tryptamine, tyramine, and 2-phenylethylamine, three amines (histamine, tyramine, and tryptamine) were not detected in any of the fish samples during the storage period. As storage time progressed, putrescine and cadaverine became the dominant amines, reaching 22.7, and 16.9 mg/kg, respectively, at 19 days of storage in ice. Total viable counts of whole gutted turbot increased from the initial value of 3.3 log cfu g⁻¹ (day 0) to 7.87 log cfu g⁻¹ (day 19) over the period of storage. If 10⁶ microorganisms/g are considered to be the TVC limit of acceptability, the shelf life of turbot was approximately ∼13–14 days.     

Effect of pH on the formation of edible films made from the muscle proteins of Blue marlin (Makaira mazara)

Whole meat of Blue marlin (Makaira mazara) was used to prepare edible films. Protein solubility in film-forming solutions was high at acidic and alkaline pHs, while that at neutral pH was close to zero. Acidic and alkaline pHs improved the tensile strength while the effects of pH, on elongation at break, water vapour permeability and light transmission of the films, were not significant. From the film solubility in various protein denaturants it was revealed that the main interaction responsible for the formation of acidic and alkaline pH films was hydrophobic interaction, while that for neutral pH films was ionic bonding.     

The effects of pretreatments on antioxidative activities of protein hydrolysate from the muscle of brownstripe red snapper (Lutjanus vitta)

Different pretreatments of mince from brownstripe red snapper (Lutjanus vitta) including 1) washing; 2) membrane separation; 3) washing followed by membrane separation and 4) membrane separation followed by washing were conducted prior to hydrolysis. Among the resulting minces, that subjected to membrane separation with subsequent washing (MS/W) contained the lowest remaining myoglobin content, phospholipid content, heme iron and non-heme iron contents (p < 0.05) and showed the lowest TBARS values throughout 9 days of storage at 4 °C in the presence and absence of 0.15 mol L⁻¹ cupric acetate (p < 0.05). When hydrolysates from 1) mince, 2) MS/W and 3) protein isolate from MS/W (PI) with different degree of hydrolysis (DH) (20, 30 and 40%) were prepared using proteases from pyloric caeca of brownstripe red snapper, antioxidative activities determined by DPPH, ABTS radical scavenging activities, ferric reducing antioxidant power and metal chelating activity varied with hydrolysates and DH. Antioxidative activities increased with increasing DH up to 40% (p < 0.05). At all DH tested, hydrolysate prepared from MS/W exhibited the highest antioxidative activities determined by all assays, compared to those from mince and PI (p < 0.05). Hydrolysate from MS/W with 40% DH had the molecular weight lower than 6.5 kDa as determined by SDS-PAGE. In liposome oxidation system, the addition of hydrolysate from MS/W resulted in the lower TBARS, compared with the control throughout the incubation period of 48 h at room temperature (25-28 °C). Therefore, fish mince with membrane separation followed by washing was the most appropriate source for production of hydrolysate possessing antioxidative activity with the lowered amount of lipids and pro-oxidants.