Processing of Salted Cod (Gadusspp.): A Review

The Effects of Postmortem Time on Muscle Trout Biochemical Composition and Structure

Fish industry operators have to process fish that arrive at various postmortem times. Postmortem time constrains processing and impacts product quality, safety, and economic value. The objective identification of biomarkers is desirable to predict the postmortem day of aging and this requires a comprehensive longitudinal characterisation of postmortem aging. We analysed the postmortem aging process in trout over a 15-day window. Quantitative physicochemical measurements (pH, colour, texture, a_w, proteolysis, and myofibrillar protein solubility) performed on the same fish over time revealed the levels of protein denaturation, solubility, and pH, among other parameters, change very little when assessed by conventional chemical methods. Histological analyses were performed on thin sections and revealed fibre ruptures after 7 days of storage on ice. Ultrastructures were observed by transmission electronic microscopy (TEM) and revealed that sarcomere disorganisation occurred more often after 7 days of storage. Label-free FTIR micro-spectroscopy combined with a SVM model accurately predicted the postmortem time. Spectra-based PC-DA models also enable the identification of biomarkers corresponding to Day 7 and Day 15 postmortem. This study provides insights on postmortem aging and raises prospects for the rapid assessment of trout's freshness status from label-free imaging.

The Effect of the Species and Harvesting Location on Dried Salted Cod Fatty Acid Signatures and Nutritional Quality

The Atlantic cod was listed as 'vulnerable' by the International Union for Conservation of Nature, a condition that persists today. Fishing pressure on the Atlantic cod could be partially transferred to the Pacific cod, since the two cod species share genetic and phenotypic similarities. The aim of this study is to expand knowledge of the composition of dried salted cod obtained from Atlantic and Pacific cod species, with the Atlantic cod being from two different harvesting locations. The comparison of these cod species revealed the existence of nine significant differences among individual FAs (accountable for 63.2% of total FAs), which was at a similar level to that observed between different harvesting locations for the Atlantic cod (ten significant differences among individual FAs, accountable for 61.6% of total FAs). Canonical discriminant analysis and cross-validation achieved full discrimination of the cod's origin and 100% accuracy in the cod's origin classification. The amount of EPA plus DHA in dried salted cod reached its higher value among the Pacific cod (302.3 mg/100 g), while the Atlantic cod averaged 284.1 g/100 g of edible portion. The Pacific cod presented a higher α-tocopherol content than its Atlantic counterpart (8.04 vs. 4.94 µg/g).

Evaluating dried salted cod amino acid signature for nutritional quality assessment and discriminant analysis

Aim

Thus, the aim of this study was to answer three scientific questions: (1) Are the protein content and amino acid profile of dried salted cod influenced by species (Gadus morhua and Gadus macrocephalus)? (2) Are the protein content and amino acid profile of dried salted cod influenced by the geographical area of capture (Iceland and Norway)? and (3) Does the amino acid profile have the potential to be used as a discriminator of species and geographical areas of capture?

Methods

A total of 45 dried salted cods (2-3 kg of dry weight; n = 15 samples/origin) were used in this study. The Atlantic cod was fished in the Atlantic northeast (FAO 27 area) within the Exclusive Economic zones (EEZ) of Norway (n = 15) and Iceland (n = 15), while the Pacific cod was caught in the Pacific northeast (FAO 67 area) within the Alaska EEZ (n = 15). Total protein content was determined by the Kjeldahl method, in accordance with the AOAC procedures. The amino acid profile was analyzed by HPLC with fluorescence detection (at excitation and emission wavelengths of 338 and 425 nm, respectively).

Results

The Atlantic cod presented higher contents of total protein (33.90 versus 33.10 g/100 g of cod edible portion; p = 0.017) and total amino acid contents (32.52 versus 32.04 g/100 g of cod edible portion; p = 0.015) but displayed lower percentage of indispensable amino acids (32.16 versus 32.83 g/100 g of protein; p < 0.001) than Pacific cod. Among the Atlantic cod harvesting locations, the Norwegian cod displayed higher total amino acid contents (96.91 versus 96.81 g/100 g of protein; p = 0.012) and higher percentage of indispensable amino acids (35.38 versus 28.94 g/100 g of protein; p = 0.042) than the Icelandic counterpart. A correct classification of 100% was obtained for the Pacific and Icelandic cod varieties, but the classification accuracy in the Norwegian cod was of just 86.67%, since 2 samples out of 15 were incorrectly classified as Icelandic.

Conclusion

The comparison of cod species showed that the Atlantic cod had a significantly lower EAAI than the Pacific cod (p < 0.001; 88.23 versus 88.61). On the other hand, the comparison of the two origins in the Atlantic cod, showed that Norwegian cod displayed a significantly higher EAAI than the Icelandic cod (99.15 versus 77.32). The assessment of the EAAI allows the classification of the protein's nutritional quality, allowing us to classify both cod species as a good protein source to human diet. However, within the Atlantic cod, the Norwegian cod's protein is classified as high quality, while the Icelandic cod attain the classification of useful quality. Regarding the amino acid profile discriminatory potential to classify cod samples. The results show that the AA profile has 100% accuracy in the separation of cod species, but was not globally efficient in the differentiation of the Norwegian from the Icelandic cod.

Effect of dry salt versus brine injection plus dry salt on the physicochemical characteristics of smoked salmon after filleting

Smoked fish fillets are pre-salted as a food conservation and quality preservation measure. Here we investigated biochemical and sensory aspects of smoked salmon fillets. Left-side salmon fillets were dry-salted while the right-side fillets underwent a mixed salting method consisting of an injection of saturated brine followed by surface application of dry salt. After 6 h of salting, all the fillets were smoked. At each step of the process, quality was evaluated using instrumental measurements (pH, color, texture, water content, salt content, a_w), and lipid distribution was visualized by MRI. Mixed-salted fillets had a higher salt content than dry-salted fillets and variability in salt distribution was dependent on the salting process. However, these variations had no effect on pH, color or texture, which showed similar values regardless of salting method. Fatty areas had a lower salt content due to slower diffusion of aqueous salt solutions through them. Mixed salting speeds up the salting of the muscle without significantly affecting the quality traits of the salmon fillet.

Understanding the effects of ultrasound processng on texture and rheological properties of food

The demand for the production of high quality and safe food products has been ever increasing. Consequently, the industry is looking for novel technologies in food processing operations that are cost-effective, rapid and have a better efficiency over traditional methods. Ultrasound is well-known technology to enhance the rate of heat and mass transfer providing a high end-product quality, at just a fraction of time and energy normally required for conventional methods. The irradiation of foods with ultrasound creates acoustic cavitation that has been used to cause desirable changes in the treated products. The technology is being successfully used in various unit operations such as sterilization, pasteurization, extraction, drying, emulsification, degassing, enhancing oxidation, thawing, freezing and crystallization, brining, pickling, foaming and rehydration, and so forth. However, the high pressure and temperature associated with the cavitation process is expected to induce some changes in the textural and rheological properties of foods which form an important aspect of product quality in terms of consumer acceptability. The present review is aimed to focus on the effects of ultrasound processing on the textural and rheological properties of food products and how these properties are influenced by the process variables.

Dry-salted cod (Gadus morhua) rehydration assisted by pulsed electric fields: modelling of mass transfer kinetics

BACKGROUND

Dry-salted cod (Gadus morhua) must be rehydrated before consumption and this step can take up to 5 days. Desalting of cod on an industrial scale poses many problems, mainly related to the long processing times and the quality of the final product. For this reason, many researchers have focused on finding new desalting methods to improve mass transfer. The application of pulsed electric fields (PEF) has been proposed as an alternative method for improving mass transfer in many food processes. However, there is no previous literature on the use of PEF to improve animal tissue rehydration. Therefore, the present study aimed to investigate the influence of two PEF pre-treatments [PEF (1) 500 V cm^-1 and PEF (2) 1000 V cm^-1 ] on mass transport kinetics during the rehydration process of salted cod. The rehydration process was carried out under static conditions for 6 days, immersing dry-salted cod samples in tap water (5 ± 0.5 °C).

RESULTS

The results show that the use of PEF technology increases the rate of the rehydration process of dry-salted cod and influences the redistribution of salt. In general, the samples pre-treated with PEF showed higher weight gain and lower salt loss than the control samples during the rehydration process.

CONCLUSION

The application of PEF prior to rehydration of salted cod samples could be of interest to the food industry as a result of a higher process yield (higher weight gain) and the possibility to reduce the water renewal because less NaCl is lost in the wastewater. © 2022 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Improvement of Pacific White Shrimp (Litopenaeus vannamei) Drying Characteristics and Quality Attributes by a Combination of Salting Pretreatment and Microwave

This study investigated the effects of salting pretreatment and microwave (MW) power on drying characteristics, water distribution and quality attributes of Pacific white shrimp (Litopenaeus vannamei). With increasing salt concentration (0–8%, w/v) and MW power (300–900 W), the drying time of shrimp was shortened by 15.15–28.57%, compared with the untreated samples. Regarding the quality of dried shrimp, increasing the salt concentration and MW power increased the hardness (from 13,073.6 to 24,556.5 g), while the springiness, color parameters and astaxanthin content showed an initial decrease but a later increase trend. Low field nuclear magnetic resonance (LF-NMR) demonstrated that the T₂ curve of the pretreated samples moved toward the negative x-axis and the immobilized water content decreased with increasing salt concentration. E-nose showed that volatile components were different and could be obviously distinguished at different salt concentrations and MW powers. Raman spectroscopy illustrated that the protein secondary structure of dried shrimp was altered by salting pretreatment and drying conditions, and the lowest conversion degree of α-helix to β-sheet of dried shrimp was obtained at the salt concentration of 4% (w/v) and MW power of 500 W. By comprehensively considering the drying time and quality attributes, the combination of 4% (w/v) salt and 500 W MW power was concluded as the best drying conditions for shrimp using a microwave. The results could provide an innovative combination of salt pretreatment and MW drying with suitable processing conditions for producing high-quality dried shrimp.

Structure of fish proteins as modified by salting procedures: A rheological and ultrastructural analysis of hake (Merluccius hubbsi) fillets

Salting is a technique used for preserving fish meat and allows obtaining added value products. The salting process provokes several structure modifications, which in turns cause changes in the fish texture. Thus, the objective of this study was to investigate the effect of three salting procedures (dry salting [DS], mixed salting [MS] and brining [BS]) on the rheology and structure of Merluccius hubbsi (Argentine hake). Rheological properties were evaluated using dynamic oscillatory and thermorheology tests, and the structure changes by scanning electron microscopy. DS samples showed the highest values of salt concentration referred to liquid phase (z_NaCl ), while BS showed the lowest ones. In all cases, elastic (G') and loss (G″) modulus increased with salting time. G' values exceeded G″ values, indicating a predominant solid behavior. DS samples presented the greatest increase in rheological parameters (G', G″ and η*). Thermomechanical spectra allowed to identify an increase in denaturation temperature (Td) of proteins (myosin and actin) for DS and MS, and to a lesser extent for BS (Td = 46.7 ± 0.4°C, Td = 50.3 ± 0.8°C, Td = 58.8 ± 0.6°C and Td = 58.2 ± 0.9°C for fresh, BS, MS and DS, respectively). Ultrastructural images evidenced conformational changes on the myofibrillar proteins and the connective tissue (collagen). BS caused the least superficial damage to hake tissue. Based on the results, BS could be the method recommended for the industrial production of salted M. hubbsi. PRACTICAL APPLICATION: During salting of hake, variations in water and salt content have a significant effect on the myofibrillar and connective tissue proteins. The study of rheological properties and microstructure allows a better understanding of the conformational changes induced by the salting process. The least surface damage exhibited by brining fillets is consistent with the mass transfer mechanism that leads to the formation of a film on the muscle surface that dilutes the salt; for this reason, compared to dry and mixed salting, brining could be the method recommended for the industrial production of salted (>15% w/w) Merluccius hubbsi.

Undesirable discoloration in edible fish muscle: Impact of indigenous pigments, chemical reactions, processing, and its prevention

Fish is rich in proteins and lipids, especially those containing polyunsaturated fatty acids, which made them vulnerable to chemical or microbial changes associated with quality loss. Meat color is one of vital criteria indicating the freshness, quality, and acceptability of the meat. Color of meat is governed by the presence of various pigments such as hemoglobin, myoglobin (Mb), and so on. Mb, particularly oxy-form, is responsible for the bright red color of fish muscle, especially tuna, and dark fleshed fish, while astaxanthin (AXT) directly determines the color of salmonids muscle. Microbial spoilage and chemical changes such as oxidation of lipid/proteins result in the autoxidation of Mb or fading of AXT, leading to undesirable color with lower acceptability. The discoloration has been affected by chemical composition, post-harvesting handling or storage, processing, cooking, and so on . To tackle discoloration of fish meat, vacuum or modified atmospheric packaging, low- or ultralow-temperature storage, uses of artificial and natural additives have been employed. This review article provides information regarding the factors affecting color and other quality aspects of fish muscle. Moreover, promising methodologies used to control discoloration are also focused.

Effect of Cold Smoking and Natural Antioxidants on Quality Traits, Safety and Shelf Life of Farmed Meagre (Argyrosomus regius) Fillets, as a Strategy to Diversify Aquaculture Products

Aquaculture has been playing a leading role over the years to satisfy the global growing demand for seafood. Moreover, innovative techniques are necessary to increase the competitiveness, sustainability and profitability of the seafood production chain, exploiting new species from the aquaculture, such as meagre (Argyrosomus regius), to develop value-added products and diversify their production. In the present work, the effectiveness of cold smoking combined with antioxidants (SA) compared to cold smoking alone (S) on meagre fillets, the quality and shelf life were investigated. Sensory, biochemical, physical–chemical and microbiological analyses were performed on the smoked fillets during vacuum-packaged storage for 35 days at 4 ± 0.5 °C. The results showed positive effects of the SA treatment on the biochemical parameters of meagre fillets. The total volatile basic nitrogen (TVB-N) in smoked meagre fillets was significantly lower in the SA treatment at the end of storage compared to the S treatment. Moreover, SA had a positive effect on lipid peroxidation. Lower values of malondialdehyde (mg MDA/kg) were observed in the SA treatment during preservation compared to the S treatment. This work will contribute to the growth of the fish production chain, producing a value-added fish product by exploiting meagre, whose production has been increasing over decades.

Effect of salting procedures on quality of hake (Merluccius hubbsi) fillets

The influence of salting procedures on the proximate analysis, mechanical parameters, and color of hake (Merluccius hubbsi) was investigated. Three procedures were comparatively evaluated: dry salting (DS), mixed salting (MS) and brining (BS). MS samples had the highest fat content, a considerable protein content and an equilibrium salt content similar to BS. MS samples had a great water loss, as DS method, but hardness and other mechanical parameters were similar to that obtained with BS, i.e. significantly lower than DS. All samples showed color parameters significantly different as compared to fresh hake, turning more red-orange as the salting time increased. Lightness diminished, a∗ values increased and b∗ values did not show a clear trend throughout the salting time. Principal component analysis (PCA) described the relationship between some variables (z_NaCl, color, and mechanical parameters) with salting time. High Pearson's correlation coefficients were found between z_NaCl and hardness, springiness, cohesiveness and a∗ parameter (r = 0.76, p < 0.001; r = 0.93, p < 0.0001; r = 0.95, p < 0.001 and r = 0.93, p < 0.0001, respectively). Luminosity was negatively correlated with z_NaCl (r = -0.87, p = 0.0001). The correlation curves showed nonlinear relationships (R²_adj between 83.7 % and 97.4 %), which could be used to predict quality attributes of hake fillets as a function of salting time. This work contributed to know the effect of different salting procedures on the quality attributes of a species widely available in the Southwest Atlantic Ocean.

Effects of traditional fish processing methods on the proximate composition and ph of fish Black pomfret (Parastromateus niger)

Fish is an important food in many Iranian diets. This is a good source of protein. Fish is the main source of animal protein in Iran. The effects of three different traditional processing methods (freezing, brining and frying) on nutritive composition of halva sia fish stored under ambient room conditions were determined. Fresh halva sia fish were obtained from Behbahan fish market. Cooking and processing techniques were carried out on fish Halva sia Parastromateus niger. The proximate composition of raw Parastromateus niger was affected by cooking and processing techniques that were carried out by AOAC methods. Moisture contents decreased in fried and brined fillet while protein, fat and ash contents were significantly increased in fried fillet. The loss of moisture in fried and brined samples amounted to the highest levels; also the protein and fat value was proportionally high. The fish Parastromateus niger showed a decrease in their contents of moisture and fat as affected by frozen storage periods while ash and protein contents were increased after frozen storage periods. The nutritional value fish Parastromateus niger preserved until the end of the storage period.

Polyphosphates changes in dried salted cod (Gadus morhua) during industrial and domestic processing

Changes in added polyphosphates throughout the processing of dried salted cod in industrial environment were evaluated. As consumers purchase both dried salted cod and desalted cod, domestic and industrial desalting processes were performed. After brining, total phosphates increased to 11.6 and 16.6 g P₂O₅/kg in cod processed with 3 and 6% of polyphosphates, respectively. During dry-salting, total phosphates decreased in both cases to ca. 5 g P₂O₅/kg, suggesting that most polyphosphates were drained with the water released. Cod with polyphosphates needed 85 h extra drying time to achieve regulatory moisture levels. After desalting, total phosphates values in dry weight indicate that phosphates were not removed during this processing step. Free phosphates, and in particular triphosphate contents, were higher in cods desalted following domestic procedures, in comparison with industrial desalting. This study demonstrates that the use of polyphosphates is not recommended for the production of Portuguese dried salted cod. These additives prevent water from being removed during the drying process, increasing the costs. Moreover, in contrast to what was assumed, part of polyphosphates is retained in the final product, even after the desalting process.

Morphological and molecular diagnosis of Pseudoterranova decipiens (sensu stricto) (Anisakidae) in imported cod sold in Brazil

An anisakid nematode larva found in cod sold in the state of Minas Gerais, Brazil was studied by light and scanning electron microscopy and by a molecular approach. Mitochondrial cytochrome c-oxidase subunit 2 (mtDNA cox-2), 28S rRNA and ITS1, 5.8S and ITS2 regions were amplified using the polymerase chain reaction and sequenced to evaluate the phylogenetic relationships of the larva. The genetic profile confirmed that this larva belongs to the species Pseudoterranova decipiens (sensu stricto). This is the first molecular and ultrastructural study of Pseudoterranova decipiens (sensu stricto) in imported cod sold in Brazil. The health implications of these findings are discussed.

Effect of sodium bicarbonate and varying concentrations of sodium chloride in brine on the liquid retention of fish (Pollachius virens L.) muscle

BACKGROUND

Negative health effects associated with excessive sodium (Na) intake have increased the demand for tasty low-Na products (<2% NaCl) rather than traditional heavily salted fish products (∼20% NaCl). This study investigates the causes of improved yield and liquid retention of fish muscle brined with a combination of salt (NaCl) and sodium bicarbonate (NaHCO3 ).

RESULTS

Water characteristics and microstructure of saithe (Pollachius virens L.) muscle brined in solutions of NaCl and NaHCO3 or NaCl alone were compared using low-field nuclear magnetic resonance (LF-NMR) T2 relaxometry, microscopy, salt content, liquid retention and colorimetric measurements. Saithe muscle was brined for 92 h in 0, 30, 60, 120 or 240 g kg(-1) NaCl or the respective solutions with added 7.5 g kg(-1) NaHCO3 . NaHCO3 inclusion improved the yield in solutions ranging from 0 to 120 g kg(-1) NaCl, with the most pronounced effect being observed at 30 g kg(-1) NaCl. The changes in yield were reflected in water mobility, with significantly shorter T2 relaxation times in all corresponding brine concentrations. Salt-dependent microstructural changes were revealed by light microscopy, where NaHCO3 supplementation resulted in greater intracellular space at 30 and 60 g kg(-1) NaCl.

CONCLUSION

Sodium bicarbonate addition to low-salt solutions can improve yield and flesh quality of fish muscle owing to altered water mobility and wider space between the muscle cells.

Molecular analysis of skin bacterial assemblages from codfish and pollock after dry-salted fish production

Dry-salted codfish and pollock are commercially important food products with a relatively long shelf life. To date, bacterial assemblages present in these products that are relevant for food safety have been monitored using only classical molecular and/or cultivation methods. The present study employed a rapid and accurate identification method involving PCR with denaturing gradient gel electrophoresis and pyrosequencing to characterize the bacterial assemblages in the skin of three closely related fishes: Gadus morhua, Gadus macrocephalus, and Theragra chalcogramma. This methodology can be crucial for timely identification of food spoilage, hazard analysis, and monitoring of critical control points during food production. Although all specimens were processed in the same factory, there were significant compositional differences in their skin bacterial communities. In general, the bacterial community was dominated by gram-negative species of the Gammaproteobacteria. Pyrosequencing yielded 90, 69, and 245 operational taxonomic units associated with G. morhua, G. macrocephalus, and T. chalcogramma, respectively. The most dominant operational taxonomic units were assigned in order to Pseudomonas sp., Serratia marcescens, Salinisphaera sp., and Psychrobacter pulmonis. Spoilage and pathogenic bacterial groups were detected in all the studied salted gadoid samples.