Changes in protein fractions of rainbow trout (Oncorhynchus mykiss) gravads during production and storage

Gravad fish products belong to a group of low-processed products obtained from fresh fish by sprinkling fillets with a mixture of sugar and salt and then placing them in cold storage. Little is known about changes in the tissue during the production and storage of gravads. The purpose of the present study was to investigate the type and scope of changes in rainbow trout (Oncorhynchus mykiss) gravad proteins during processing and vacuum storage at 3 °C and −30 °C. The results showed that the solubility of protein was barely affected by the gravading process, but did change during the cold storage and freezing of the gravad. Catheptic activity decreased with gravading and further storage. A SDS-PAGE analysis revealed that the intensity of the M-protein and troponin bands was reduced, while the bands of α-tropomyosin and the myosin heavy chain increased when the trout muscle was subjected to the gravading process. Two bands with molecular weights of 255 and 135 kDa disappeared in the gravad, and new bands with molecular weights of 163 and 117 kDa appeared. An HPLC analysis revealed that gravading had a limited effect on the relative areas of peaks corresponding to low molecular weight substances of protein origin, while more significant changes were observed during gravad storage. Moreover, the gravading process caused a lowering of the actin and myosin denaturation temperature, which was proved using the DSC method. In conclusion, changes in rainbow trout muscle protein appeared to have a crucial effect on product quality.     

Mathematical modeling of the heat transfer process and protein denaturation during the thermal treatment of Patagonian marine crabs

Southern Ocean swimming crab Ovalipes trimaculatus and the Patagonian stone crab Platyxanthus patagonicus are fishing resources with commercial value. Thermal treatment of crabs is necessary to denature muscle proteins, facilitating meat detachment from the crab shell (picking procedure). The proximal composition, protein patterns of crab muscle, thermophysical properties and heat transfer coefficients were determined. Heat transfer during thermal processing of body (i.e., cephalothorax) and claws of both crab species was simulated using a finite element computational code; the simulations were experimentally validated. Color changes in crab muscle during the heating process were measured. Thermal denaturation kinetics of myofibrillar proteins was determined using Differential Scanning Calorimetry (DSC) in small samples previously heated in water under controlled conditions. DSC thermograms of raw crab muscle showed two peaks at 49.0 ± 0.4 and 77.5 ± 0.6 °C corresponding to myosin and actin respectively. Activation energies for the denaturation of myosin (145.70 kJ/mol) and actin (156.42 kJ/mol) were calculated from Arrhenius equation. The degree of denaturation achieved by the myofibrillar proteins at the coldest point of the muscle in body and claws during the heating process was established by considering the protein denaturation kinetics determined by DSC, the activation energies and the heat penetration curves. Adequate conditions for the detachment of meat from the crab exoskeleton were established. The obtained results may help in determining the optimal heating times during the industrialization of these crustaceans.     

Quality loss during the frozen storage of sea salmon (Pseudopercis semifasciata). Effect of rosemary (Rosmarinus officinalis L.) extract

Lipid and protein alterations during the frozen storage (−11 °C) were analyzed in minced sea salmon muscles to evaluate the effect of the application of rosemary extract (200 and 500 mg/kg). Lipid oxidation reached maximum TBA values between 3 and 4 months of storage in untreated muscles. The main polyunsaturated fatty acids affected were 22:6-ω3, 22:5-ω3 and 20:4-ω6 acids. Phospholipid hydrolysis was also detected. Rosemary extract reduced lipid oxidation for 6 months (500 mg/kg, muscle with 10.8 g/kg lipids) or 3 months (200 mg/kg, muscle with 5.3 g/kg lipids). Myofibrillar proteins showed a decrease of extractability (80%) after 2 months of storage. Myosin denaturation was evident by DSC at 3 months, while myosin and actin peaks disappeared at 6 months. A diminution of extractable polypeptides of high molecular weight was recorded by SDS-PAGE after 3 months. The available lysine content suffered a reduction starting at 3 months of storage, suggesting some interaction involving the free amino groups of lysine. Fluorescent compounds' determination did not show changes due to the interaction of lipid oxidation products and proteins, while protein alterations could not be reduced by the rosemary extract. Furthermore, the antioxidant reduced the loss of red color in the muscle.     

Differential Scanning Calorimetry of Fish Muscle: The Effect of Processing and Species Variation

Differential Scanning Calorimetry (DSC) has been used to study the thermal properties of fish muscle proteins and to measure the extent of their denaturation under various processing conditions. Fish myosin was susceptible to denaturation by frozen storage and dehydration. Denaturation of certain fish proteins was partially reversible. Although fish myosin was very unstable, its thermal stability was found to increase in species adapted, to higher environmental temperatures.     

Quality enhancement in fresh and frozen lingcod (Ophiodon elongates) fillets by employment of fish oil incorporated chitosan coatings

The 3% chitosan solutions incorporating 10% fish oil (w/w chitosan, containing 91.2% EPA and DHA) with or without the addition of 0.8% vitamin E were prepared. Fresh lingcod (Ophiodon elongates) fillets were vacuum-impregnated in coating solution at 100 mm Hg for 10 min followed by atmospheric restoration for 15 min, dried, and then stored at 2 °C or −20 °C for 3-weeks and 3-months, respectively, for physicochemical and microbial quality evaluation. Chitosan–fish oil coating increased total lipid and omega-3 fatty acid contents of fish by about 3-fold, reduced TBARS values in both fresh and frozen samples, and also decreased drip loss of frozen samples by 14.1–27.6%. Chitosan coatings resulted in 0.37–1.19 and 0.27–1.55 log CFU/g reductions in total plate and psychrotrophic counts in cold stored and frozen stored samples, respectively. Chitosan–fish oil coatings may be used to extend shelf-life and fortify omega-3 fatty acid in lean fish.     

Effect of high-pressure versus conventional thawing on color, drip loss and texture of Atlantic salmon frozen by different methods

Atlantic salmon (Salmo salar) samples were frozen by conventional air freezing, plate freezing and liquid nitrogen (LN) freezing, and subjected to different thawing treatments: water immersion thawing (WIT) (4°C and 20°C) and high-pressure thawing (HPT) at 100, 150 and 200 MPa with water (containing 2 g oil/100 g) as pressure medium at 20°C. Temperature and phase change behavior of fish samples were monitored during freezing and thawing. The phase change point of frozen salmon was lowered to −14°C, −19°C and −25°C for the HPT processes at 100, 150 and 200 MPa, respectively. These phase change temperatures were lower than for pure ice at the same pressures possibly due to the presence of solutes in salmon. The HPT times were 22.6±1.4, 18.1±1.4 and 17.0±1.3 min at 100, 150 and 200 MPa, respectively, as compared with 26.6±2.1 and 94.3±3.4 min for the WIT process at 20°C and 4°C, respectively. Employing pressures above 150 MPa caused noticeable color changes in salmon during the HPT process and the product texture was significantly modified during HPT at 200 MPa. Different freezing rates prior to thawing resulted in differences in drip loss in salmon samples, but they did not induce specific color and texture changes. A significant (P<0.05) reduction of drip loss by the HPT process was observed only for the LN frozen samples in which mechanical cracking occurred and much of the drip appeared after WIT process. Drip loss formed during pressure thawing seems to be a complicated process, for which further studies are needed.     

Quality of superchilled vacuum packed Atlantic salmon (Salmo salar) fillets stored at −1.4 and −3.6 °C

The most important factor for increasing shelf life is the product temperature, and since fish is more highly perishable than meat, the temperature is even more important. In the present study, portions of fillets of farmed Atlantic salmon (Salmo salar) were superchilled at two temperature levels, −1.4 and −3.6 °C. Texture, drip loss, liquid loss, cathepsin activities and protein extractability were investigated during storage and compared to ice chilled and frozen references. Drip loss was not a major problem in superchilled salmon. Textural hardness was significantly higher in superchilled salmon fillets stored at −3.6 °C compared to those stored at −1.4 °C, ice chilled and frozen references. Cathepsins B and B + L were not deactivated at the selected storage temperatures. The storage time of vacuum packed salmon fillets can be doubled by superchilled storage at −1.4 °C and −3.6 °C compared to ice chilled storage.     

Protein Structural Changes During Preparation and Storage of Surimi

The changes in protein structure associated with the preparation and frozen storage of surimi were investigated. Raw surimi was prepared by repeatedly washing Alaska pollock flesh with chilled water. The product was either slowly frozen or underwent rapid freezing using liquid air; in either case it was then subjected to frozen storage at ‐20 °C for 24 mo. Fourier transform infrared/attenuated total reflectance (FTIR/ATR) spectroscopy showed that during preparation of surimi, the a‐helix content increased with increased number of washing cycles. Differential scanning calorimetry (DSC) revealed a shift in the thermal transition of actin to a higher temperature during surimi preparation. Electrophoresis, FTIR/ATR spectroscopy, and DSC results revealed a loss of myofibrillar proteins from surimi after 3 washing cycles, suggesting that 3 washing cycles were adequate to prepare surimi. Sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE) showed relatively minor changes in protein subunit structure with some loss of the myosin light chains (MLC); myosin heavy chain (MHC), actin, and tropomyosin were found to be relatively stable. Native‐PAGE showed no major changes in surimi after 24 mo storage at ‐20 °C. FTIR/ ATR spectroscopy indicated a significant decrease in a‐helix relative to p‐sheet structure in surimi after 2 y of storage at ‐20 °C. The loss of α‐helical content was more significant in slowly frozen surimi compared with rapid‐frozen surimi samples. DSC results revealed a shift in the thermal transition of actin to lower temperatures during frozen storage of surimi.     

Effect of freezing rate on the denaturation of myofibrillar proteins

Freezing of bovine muscle has a denaturating effect on myofibrillar proteins, Differ-ential Scanning Calorimetry (DSC) studies of fresh and frozen muscle at different freezing rates show a decrease on denaturation enthalpies; the lower the freezing rate the greater the loss. When measuring the specific areas (ratio between each partial area in cm', and the dry weight of the sample, in mg) of the DSC thermograms, it can be observed that the area ascribed to myosin decreases with freezing, while the area corresponding to actin is not affected. These results are in agreement with the ATPase activity decreases as a consequence of freezing observing higher losses at lower freezing rates. The denaturation observed could be a result of a partial unfolding of the myosin head being more pronounced at low freezing rate.     

Effects of sodium bicarbonate containing traces of citric acid in combination with sodium chloride on yield and some properties of white shrimp (Penaeus vannamei) frozen by shelf freezing, air-blast and cryogenic freezing

Effects of sodium bicarbonate with traces of citric acid in combination with sodium chloride on yield, freezing time, freezing rate, freezing loss and cutting force of white shrimp frozen by shelf, air-blast and cryogenic freezing with/without precooking were investigated. Shelf freezing was done at −40 °C ± 2 °C while air-blast freezing was carried out at −35 °C ± 2 °C, and cryogenic freezing was done at −35 °C, −40 °C and −60 °C. The freezing loss in the non-treated samples was 8.25, 4.6-5.84 and 1.92-3.48 g/100 g fresh shrimp for peeled samples frozen without precooking and increased to 21.85, 17.54-26.97, 17.92-20.31 g/100 g fresh shrimp in the precooked samples frozen by shelf, air-blast and cryogenic freezing, respectively. The treatment of sodium bicarbonate containing traces of citric acid at 4 g/100 ml with sodium chloride at 3 g/100 ml lead to the increase of yield thus reduced the freezing loss by about 6.83-10.28 and 6.41-12.4 g/100 g fresh shrimp for the frozen-thawed samples frozen as uncooked and cooked products, respectively. The toughening of shrimp was observed while sodium bicarbonate containing traces of citric acid treatment with sodium chloride could reduce the texture change occurred during the freezing.     

Losses of nitrogen fractions from herring to brine during marinating

Fish meat is characterized by a high content of valuable nutrients. During the marinating process, however, the process of proteins diffusion and other nitrogen fractions from fish to the surrounding brine is commonly observed. It was determined that the total nitrogen loss from herring meat of industrial maturity (4-5 day) amounted to 6-19% of raw material nitrogen. Extension of the marinating time to 16-18 days increases nitrogen losses even to 18-27%. Less loss was observed during marinating of fresh than of frozen herring and during marinating of carcasses, as opposite to fillets. Higher nitrogen content in fish was not proved to influence higher nitrogen losses in a brine. The majority of loss consisted of nitrogen fractions soluble in TCA, of which one third was formed by α-amine nitrogen. Nitrogen contained in brine suspension accounted for only 1.5-4% of total nitrogen losses. With increasing salt or acid concentration the amount of total nitrogen loss was lower from fresh herring and higher from frozen one. Higher salt concentration significantly reduced the amount of non-protein nitrogen and all its fractions during marinating of fresh and frozen herring. In case of acetic acid, the influence of its concentration was diverse and depended on type of herring and its dressing.     

Interaction between fish myoglobin and myosin in vitro

Interaction between tuna myoglobin and myosins from tuna and sardine was investigated in a model system at 4 °C for up to 24 h. Both sardine and tuna myosins bound progressively with tuna myoglobin as the storage time increased (P < 0.05). The soret absorption peak was noticeable in the myoglobin–myosin mixture. The oxidation of oxymyoglobin in the presence of myosin was generally greater than that found in the absence of myosin (P < 0.05). Oxymyoglobin underwent oxidation to a greater extent in the presence of tuna myosin than sardine myosin (P < 0.05). The interaction between fish myoglobin and myosin also caused changes in reactive sulfhydryl content and altered the tryptophan fluorescent intensity. The loss in Ca²⁺-ATPase activity of myosin varied with fish species and was governed by the myoglobin added. Thus, the interaction between fish myoglobin and myosin most likely occurred as a function of time and was species-specific.     

The effect of cryoprotectants during freezing or freeze drying upon properties of washed mechanically recovered broiler meat

Mechanically recovered meat (MRM) from broilers was washed three times with water and subjected to either slow or rapid freezing or freeze-drying with, or without, the presence of cryoprotectants. Both freezing and freeze-drying reduced the functionality of the MRM when no cryoprotectants were used. Sorbitol/sucrose showed some protection of gel forming ability of frozen samples whilst sorbitol/sucrose with tripolyphosphate gave stronger gels after freezing or freeze-drying than fresh samples. Most of the loss of functionality during freezing or freeze-drying was caused by loss of solubility of myosin and to a lesser extent actin. This was supported by DSC studies. The combined presence of sorbitol/sucrose/tripolyphosphate restored most functional properties of the frozen or freeze-dried material to that of the fresh material.     

Proteolytic Activity of Muscle in Pre- and Post-Spawning Hake (Merluccius hubbsi Marini) After Frozen Storage

The proteolytic activity of fillets from fresh fish and after frozen storage of hake muscle from pre- and post-spawned fish was investigated. The autolytic activity of fresh muscle extracts from pre-spawned muscle extracts was significantly higher than that of post-spawned, except for pH 3.4 and incubation temperature of 60 °C where no significant difference was found. In both gonadal conditions, the freezing of hake fillets affected the proteolytic activity of crude muscle extracts. After 50 d of frozen storage, the proteolytic activity values of crude muscle extracts remained higher than the fresh values, except for pre-spawned extracts incubated at 37 °C. At longer storage period (110 d), the proteolytic activity continued with similar or higher values compared with those observed for fresh muscle extracts. Densitometric analysis of crude muscle extracts indicated degradation of MHC in fresh and frozen storage at both gonadal conditions under incubation conditions of pH 6.2 and temperatures 37 and 60 °C, pH 8.5 and temperatures 37 and 60 °C, pH 3.4 and temperature 4 °C.     

Myosin heavy chain degradation during post mortem storage of Atlantic cod (Gadus morhua L.)

Post mortem proteolytic degradation of fish fillets leads to textural changes like muscle softening and gaping. In this study proteolytic degradation of myosin heavy chain (MHC) was monitored during storage of muscle and of isolated myofibrils at different temperatures and pH-values by the use of MHC-specific antibodies. The ability of cathepsin D to associate to myofibrillar proteins was also studied. Muscle stored at 6 °C and isolated myofibrils stored at 0 °C, 6 °C and 20 °C were degraded at pH 6.3 or lower. Cathepsin D could be found associated with extensively washed myofibrils. Inhibition of cathepsin D during storage affected the observed MHC-degradation at pH 5.5, but not at pH 6.3. This indicates that cathepsin D to a less extend than formerly believed, is responsible post mortem degradation of MHC.     

Rancidity development in frozen pelagic fish: Influence of slurry ice as preliminary chilling treatment

The slurry ice technology has shown profitable advantages when employed instead of traditional flake ice for the manufacture of chilled aquatic species. The present work is aimed at evaluating the effect of slurry ice as a preliminary treatment prior to frozen storage. For it, specimens of a small pelagic fatty fish species (sardine; Sardina pilchardus) were stored in slurry ice for 2, 5 and 9 days, then subjected to freezing (-80 °C; 24 h) and finally kept frozen (−20 °C) during 1, 2 and 4 months. At such times, rancidity development in frozen sardine was measured by sensory (odour, skin, colour and flesh appearance) and biochemical (lipid hydrolysis and oxidation) analyses and compared to a control batch previously chilled in flake ice. Sensory analysis indicated an extended shelf-life time for frozen sardine that was preliminary stored under slurry ice for 2, 5 or 9 days, as compared to their counterparts subjected to flake icing. Sensory results were corroborated (P<0.05) by biochemical lipid oxidation indices (thiobarbituric acid reactive substances and the fluorescence formation). The present work opens the way to the use of slurry ice instead of flake ice as preliminary treatment of fish material prior to the frozen storage.     

Oxidation desensitizes actomyosin to magnesium pyrophosphate-induced dissociation

This study aimed to establish the influence of protein oxidation on the ability of magnesium pyrophosphate (PP) to dissociate actomyosin. Actomyosin isolated from pork muscle then suspended in 0.1 M NaCl at pH 6.2 was oxidatively stressed with 10 μM FeCl₃/0.1 mM ascorbate/1 mM H₂O₂ for 6 or 12 h at 4 °C. Protein oxidation was evidenced by the loss of myosin and actin, the concomitant formation of disulphide-cross-linked polymers, and elevated myosin ATPase activity. The intrinsic viscosity of oxidized actomyosin had a weaker response to PP-Mg²⁺ than that of non-oxidized actomyosin, indicating the suppression of actomyosin dissociation. Moreover, oxidized actomyosin solutions were devoid of small particles (<10 nm) and the stressed actomyosin exhibited weaker binding of PP-Mg²⁺ than non-oxidized, which further suggested a reduced myosin–PP interaction and subsequent dissociation of the actomyosin complexes.     

Free-radical-scavenging activity and total phenols of noni (Morinda citrifolia L.) juice and powder in processing and storage

The fresh juice of noni (Morinda citrifolia L.), a tropical plant used as a folk medicine in Pacific islands, possessed free-radical-scavenging activity (RSA), 1,1-diphenyl-2-picrylhydrazyl (DPPH), at 140 mg equivalent ascorbic acid/100 ml and total phenols at 210 mg gallic acid/100 ml. Fermentation of noni fruit for 3 months resulted in a loss of more than 90% of RSA. Dehydration at 50 °C produced a loss of 20% of RSA. Storage of fresh noni juice at 24 °C for 3 months reduced RSA more than 90%. Storage of noni juice or powder at −18 °C and 4 °C for 3 months decreased RSA by 10–55%. The reduction of RSA of noni juice or purée during heat treatment or dehydration was much greater than reduction of total phenols. For maintenance of the substantial antioxidant properties of noni products, processing of noni powder or fresh frozen noni juice rather than fermented noni juice is recommended.     

Untersuchung über Änderungen von Fleischproteinen während der Gefrierlagerung

Investigation of changes in meat proteins during frozen storage. The effect of freezing and frozen storage on proteins was investigated in case of pork L. dorsi muscle. After fresh pork was sliced (1 cm thickness), wrapped and frozen (2 different velocities) samples were taken (control, 48 h-, 2, 4 and 6 month-frozen storage) and changes in proteins investigated by DSC and SDS-PAGE. DSC-thermograms show 4 peaks corresponding to myosin (peak 1) and actin (peak 4). Peak 2 reflects the sarcoplasmic proteins and connective tissue contribution. Peak 3 is not defined. When measuring the enthalpies of the DSC-thermograms, it can be observed that the enthalpy ascribed to myosin decreases during frozen storage, while the enthalpy corresponding to actin is not affected. At the beginning of our experiments SDS-PAGE was supposed to be a proper method for the investigation of protein denaturation. Our results show no significant changes in the electropherograms during the whole period of frozen storage.     

The use of water and ice with bactericide to prevent onboard and onshore spoilage of refrigerated megrim (Lepidorhombus whiffiagonis)

This study investigates the effectiveness of ozonated water and flake ice (combined Petfrost system) to increase the quality and stability of fresh megrim on fishing boats. The captured fish were washed, placed in plastic boxes, covered with flake ice and refrigerated at 2 °C for up to 2-weeks onboard and, thereafter, for 11 days onshore. The experiments employed sterile, filtered and ozonated water at a concentration of 2 ppm for washing the fish and making the flake ice. The results are compared with samples from a traditional treatment consisting of water and flake ice of marine origin. Fish were caught in four different hauls, which took 14, 12, 8 and 3 days in being landed. Subsequently, fish were stored for 1, 5, 7 and 11 days at 3 °C. The different treatments were evaluated using sensory, microbiological and chemical techniques. Fish treated with ozone always showed the best quality. Megrim treated with ozone was still suitable for consumption after 14 days on board, and megrim stored for 12, 8 and 3 days on board could be stored for a further five days in the ice state once landed with an acceptable quality. In contrast, control fish were not suitable for consumption if stored for longer than three days on board.The results indicate that treatment with water and ice flakes made from sterile and ozonated water maintains the quality of fresh megrim onboard fishing boats and upon arrival onshore.