Frozen Storage of Unwashed Cod (Gadus morhua) Frame Mince with and without Kidney Tissue

Removal of kidney material was essential for a higher quality cod frame mince. The removal of kidney tissue before deboning eliminated typical “chemical” and “petroleum” type flavors and resulted in a white, less red, and higher quality unwashed frame mince. Those samples without kidney tissue had good frozen storage stability, (particularly at -40°C) and could be used as an ingredient in apropriate meat products. The length of iced storage of frames or whole cod had little effect on frame mince quality during frozen storage.     

Prediction of Quality in Frozen Cod (Gadus morhua) Fillets

Physical and chemical indices were determined on frozen cod (Gadus morhua) fillets stored for ca. 90 days at either - 12°C, - 15°C, - 22°C, - 30°C or under a set of simulated industrial fluctuating temperature conditions (SIFTC). Univariate and multivariate statistics on the quality indices gave a relationship between frozen storage textural deterioration and the chemical parameters as influenced by storage temperature. Results on the SIFTC resembled the - 12°C and - 15°C storage treatments. Chemical indices had lower activation energy values than those for the physical parameters. Ammonia, determined enzymatically, can be used as an index of frozen fish quality. The quadratic equations developed using the dependent variable of Instron raw peak force, independent of time and temperature, can predict the textural quality of frozen cod fillets.     

Thawing, Refreezing and Frozen Storage Effects on Muscle Functionality and Sensory Attributes of Frozen Cod (Gadus morhua)

Thawing and re-freezing of cod fillet blocks did not necessarily result in greater deterioration (relative to a ‘once frozen’ control) of cooked fish sensory attributes after 9 months frozen storage at –22°C. Thawed and refrozen fish muscle displayed a faster decline in myofibril protein solubility than once frozen controls and had reduced water-holding capacity but analysis of proton spin-spin relaxation times indicated no change in water location. The decline in protein solubility was not caused by complete protein unfolding. Long thawing times (30 hr) before re-freezing and storage resulted in cooked fish with more gray appearance and more stale flavor. Changes in fish muscle functionality did not enable direct inference of sensory attributes.     

Subcellular Membrane Integrity of Atlantic Cod (Gadus morhua) Myotomal Tissue: Effects of Frozen Storage

The influence of frozen storage on the ultrastructural integrity of Atlantic cod muscle tissue membranes was investigated following three methods of freezing and retention for 12 wk at - 12°C and - 35°C. In comparison to controls (0 wk), extensive membrane condensation associated with sarcoplasmic reticulum was apparent in samples stored for 12 wk at - 12°C. The effects were observed to a much lesser extent in samples retained for 12 wk at – 35°C. It was apparent that cryogenic, plate or blast freezing techniques showed no measurable influence on the observed membrane condensation and that such ultrastructural changes resulted as a consequence of relatively high (–12°C) subfreezing temperatures.     

Bulk Storage of Cod Fillets and Gutted Cod (Gadus morhua) Under Carbon Dioxide Atmosphere

The storage-life of bulk-stored cod under CO₂ atmosphere and air were compared. Gutted fish or fillets were distributed in bulk, among coolers containing 100% air or 25% CO₂-75% N₂, which were then stored at 0 ± 1°C for 20 days. Sensory assessments and chemical tests (pH, total volatile nitrogen) were carried out to estimate the raw-state quality and the bacterial spoilage. An important difference was observed between the storage life of cod under carbon dioxide atmosphere and air; microbiological and sensory assessments suggested a storage life exceeding 20 days and total volatile nitrogen results about 6–7 days under gas atmosphere, which was nearly twice as long as in air. Storage in CO₂ atmosphere was effective in inhibiting the growth of some bacteria on the fish, thereby contributing to the significant extension of the shelf life of the product.     

Effects of Added Salt, Phosphates, and Proteins on the Chemical and Physicochemical Characteristics of Frozen Cod (Gadus morhua) Fillets

ABSTRACT: Cod fillets were injected with brine, then immersed in brine with the same composition as used for injection, and finally frozen in a plate freezer. The composition of the brine varied with groups, containing phosphates (3%), salt (5%), and/or proteins (10%), soy protein concentrate, or hydrolyzed cod proteins. The fillets were stored at -24 °C for 3 mo and then thawed to evaluate the effects on yield after thawing and cooking, drip, water-holding capacity, pH, and chemical composition. Addition of proteins slightly increased the yield of thawed fillets, but salt and phosphates were more effective. Comparison of the different proteins showed that fish proteins were not as effective as soy proteins with respect to the physicochemical parameters evaluated with the exception of water-holding capacity. The use of both type of proteins resulted in a negative appearance of the fillets, such as discoloration and slimy surface.     

Sarcoplasmic Reticulum Ca2+-ATPase and Cytochrome Oxidase as Indicators of Frozen Storage in Cod (Gadus morhua)

ABSTRACT: Activities of 2 membrane-bound enzymes, Ca²⁺-ATPase from the sarcoplasmic reticulum and cytochrome oxidase from the inner mitochondria membrane, were measured during frozen storage of cod. Enzyme activities were higher in cod muscle samples frozen at −30°C than at −20°C. Freezing-induced activation of both enzymes was observed and the activation was amplified by ice storage prior to freezing. Sensory evaluation conducted at 9 mo of frozen storage showed differences between the sensory properties of cod frozen immediately after catch and frozen after 3 d of storage on ice. These results indicated that the enzymes might be useful as indicators of quality changes by frozen storage.     

Chemical and Physical Characteristics of Lightly Salted Minced Cod (Gadus morhua)

The production of a lightly salted product from minced cod was investigated. The addition of 13% salt to cod mince showed several advantages over the previously employed 25% salt treatment. The lightly salted product had a gelatinous-fibrous texture which had shape stability after drying and cooking. When dried to 30% moisture, better water binding capacity was seen during rehydration and after cooking, with improved texture as measured on the Instron instrument.     

Effect of pH on Sedimentation of Cod (Gadus morhua) Muscle Membranes

ABSTRACT: A new process solubilizes muscle proteins, making it possible to separate membranes with their oxidizable phospholipids, but it requires a high centrifugal force to separate the membranes. In this study we show that isolated cod muscle membranes could be readily sedimented at a low centrifugal g force for 15 min at pH 5 or below but not at pH 6 or higher. Isoelectric aggregation is likely to be responsible for the sedimentation of isolated membranes at these low pH values. Various consecutive pH treatments on isolated membranes showed that certain proteins were resolubilized or resuspended at a final pH of 10.5 if they had been previously exposed to pH 3,4, or 5. pH adjustment to 10.5 before adjustment to a pH of 5 or lower inhibited the sedimentation of isolated membranes. Isolated membranes added to the supernatant of homogenized muscle solubilized at pH 3 and centrifuged at 10000 × gfor 30 min also sedimented at 4000 × gfor 15 min. This was in contrast to the membranes naturally present in the solubilized homogenate. This suggests that factors other than viscosity were involved in the lack of efficient sedimentation of membranes from solubilized muscle tissue.     

Properties of Trypsin from the Pyloric Ceca of Atlantic Cod (Gadus morhua)

Trypsin (EC 3.4.21.4) was isolated from the pyloric ceca of Atlantic cod and purified to homogeneity by affinity chromatography. The enzyme catalyzed the hydrolysis of benzoyl arginine p-nitroanilide (BAPA, pH 8.2 and 25°C) such that V_max was 250 BAPA units per micromole trypsin and K_m was 1.48 mM. For the hydrolysis of tosyl arginine methyl ester (TAME, pH 8.1 and 25°C), V_max was 18.2 × 10³ TAME units/micromole trypsin, and K_m 0.22 mM. The pH and temperature optima with BAPA substrate were 7.5 and 40°C, respectively. Atlantic cod trypsin was most active and stable at alkaline pH. The enzyme was heat labile, losing more than 50% of its activity after incubation at 50°C for 30 min. Amino acid analysis of Atlantic cod trypsin revealed that the enzyme was rich in residues such as serine, glycine, glutamate and aspartate, but poor in basic amino acid residues compared to trypsins from warm blooded animals.     

High-Resolution NMR and Magnetic Resonance Imaging (MRI) Studies on Fresh and Frozen Cod ( Gadus morhua) and Haddock (Melanogrammus aeglefinus)

Changes in the fish muscle from cod ( Gadus morhua ) and haddock ( Melanogrammus aeglefinus ) were investigated by high-resolution NMR and magnetic resonance imaging (MRI). Water- and salt-soluble extracts from fish stored at −20°C and −30°C were analysed by high-resolution proton NMR and enabled the identification of metabolites including trimethylamine oxide, trimethylamine (TMA) and dimethylamine. It was not possible to detect formaldehyde by NMR either in the stored fish samples or in spiked water or salt extracts even at high levels of formaldehyde addition, probably due to polymerisation. Systematic and controlled storage trials indicated the presence of dimethylamine at around 9 months for samples stored at −20°C, whereas no changes were detected at the control storage temperature of −30°C. A comparison of cod and haddock fillets stored for 1 year at −20 and −30°C confirmed the production of dimethylamine only in cod stored at −20°C. It was interesting to note that ‘fresh’ cod and haddock samples purchased from a local supermarket showed high levels of TMA indicating a breakdown of trimethylamine oxide to TMA by bacteria. TMA was not detected in the fish fillets especially obtained for the storage trials. MRI of fresh cod and fish stored at −8 and −30°C indicated that the fish half stored at −8°C exhibited dense lines or arches which are indicative of gaps in the tissue due to possible breakdown of the connective tissue. The images of fish stored at −30°C did not indicate any differences compared with the fresh fish. MRI also showed the presence of frozen and unfrozen areas in the fish non-destructively.     

Detection of Microsomal Phospholipase Activity in Myotomal Tissue of Atlantic Cod (Gadus morhua)

Incubation of microsomes prepared from myotomal tissue of Atlantic cod yielded detectable phospholipase activity following incubation with 1,2-dipalmitoyl-9,10-[³H]-phosphatidylcholine over a period of 24 hr. No significant incidence of nonenzymatic hydrolysis was found to accompany the determined phospholipase activity. Phospholipid hydrolysis increased linearly in the presence of increasing levels of microsomal protein (0–4 mg). Optimal phospholipase enzyme activity was determined following incubation at 20°C and maximal activity was determined in the presence of 0.1 nmole unlabelled lecithin substrate. The myotomal microsome preparation of Atlantic cod proved to be a suitable model for direct evaluation of phospholipase and perhaps might be useful in evaluation of frozen storage impact on the resultant integrity of the enzyme system.     

Pacific Hake (Merluccius Productus) Hydrolysates as Cryoprotective Agents in Frozen Pacific Cod Fillet Mince

ABSTRACT:  Fish protein hydrolysates produced by proteolysis of Pacific hake ( Merluccius productus ) with Alcalase^® (FPH-A) or Flavourzyme^® (FPH-F) were investigated as a potential alternative to the 1 : 1 blend of sucrose–sorbitol (SuSo) commonly used for cryoprotection of frozen fish mince. The physicochemical properties of cod mince samples in the absence (control) or presence of 8% FPH-A, FPH-F, or SuSo were evaluated before and after 6 freeze–thaw cycles, with differences noted at the 5% significance level. Freeze–thawing of control sample increased expressible moisture (from 22% to 33%) and cook loss (from 3% to 16%). These poor water retention properties were improved in samples containing FPH or SuSo. Differential scanning calorimetry showed higher proportion of unfrozen water in freeze–thawed samples containing FPH-F or FPH-A (0.36 g/g) compared to SuSo (0.33 g/g) and control (0.24 g/g) samples. Textural analysis of cooked mince from unfrozen samples indicated greater hardness for FPH than SuSo and control samples, while freeze–thawing resulted in decreased hardness for FPH and SuSo samples. Content and surface hydrophobicity of extractable natural actomyosin (NAM) were maintained after freeze–thawing of samples containing FPH-F or SuSo, compared to 50% decrease in extractable NAM and a significant increase in surface hydrophobicity for the control. The presence of oligopeptides in both hydrolysates and the high levels of free amino acids including Asp, Glu, Arg, and Lys in FPH-F might be responsible for their cryoprotective action. This study provides strong evidence to support development of FPH as a new generation cryoprotectant to maintain quality of frozen fish.     

Stress Relaxation Test for Monitoring Post Mortem Textural Changes of Ice-stored Cod (Gadus morhua L)

ABSTRACT: The possibilities of using the stress relaxation test as a nondestructive method to monitor post-mortem textural changes of ice-stored cod have been evaluated. The stress relaxation tests were performed in gutted cod. Fish were compressed by 5% and deformation was kept constant for 60 s. The relaxation curves obtained were fitted to nonlinear and linear regression models. Nonlinear regressions with 2 or 3 exponential terms and the linear regression model could be fitted to the relaxation curve of ice-stored cod, although the three-terms exponential models gave the best results for assessing the quality of ice-stored cod (maximum relative difference ≦ 2% and R 2 > 0.999). The highest differences were found between pre-rigor and in-rigor states.     

Evaluation of Shelf Life of Superchilled Cod (Gadus morhua) Fillets and the Influence of Temperature Fluctuations During Storage on Microbial and Chemical Quality Indicators

Quality changes of aerobically packed cod fillets stored under superchilling and abusive temperature conditions were characterized by the growth of specific spoilage organisms (SSO) and the production of microbial metabolites measured by an electronic nose along with traditional sensory and chemical analysis (total volatile basic nitrogen [TVB‐N], pH). A new process based on quick contact freezing and cold air blasting was used to achieve superchilling of fillets before chilled (0.5 °C) or superchilled (‐1.5 °C) storage. Photobacterium phosphoreum dominated under temperature abusive conditions coinciding with high levels of TVB‐N and increased electronic nose responses indicating increased levels of alcohols and aldehydes at sensory rejection. Dominating growth of Pseudomonas spp. in 1 batch was associated with the origin, the catching method, and the cooling conditions during processing. The superchilling process followed by superchilled storage (‐1.5 °C) extended the sensory shelf life of the fillets for at least 3 d compared with traditional process, resulting in a total shelf life of 15 d. High content of TVB‐N was observed in superchilled fillets at sensory rejection. P. phosphoreum counts were lower under superchilling conditions (6.0 to 6.8 log colony‐forming units [CFU]/g), compared with the traditionally processed chilled fillets (7.2 log CFU/g). However, H₂S‐producing bacteria appeared to grow steadily under superchilling conditions reaching counts as high as 7.6 log CFU/g at sensory rejection.     

Cryoprotective Effects of Lactitol, Palatinit and Polydextrose® on Cod Surimi Proteins during Frozen Storage

The cryoprotective effects of lactitol dihydrate, Polydextrose® and Palatinit (Isomalt) at 8% w/w in codsurimi were compared to an industrial control containing a sucrose/sorbitol 1:1 mixture and a control without additive. Surimi was stored at ?20°C for 12 wk and examined for freeze-induced protein changes every 2 wk by salt extractable protein and differential scanning calorimetry analyses: Palatinit®, lactitol and Polydextrose® stabilized surimi proteins equally well as did the sucrose/sorbitol mixture. Salt extractable protein and myosin peak enthalpy for surimi were maintained at the same level as the industrial control. Confirming earlier results, initial T_max-myosin yielded information regarding surimi protein stability over extended periods of frozen storage.     

Effects of Phosphate on Yield, Quality, and Water-Holding Capacity in the Processing of Salted Cod (Gadus morhua)

ABSTRACT: Fillets of cod ( Gadus morhua ) were salted in a traditional way and with the addition of polyphosphates. After 3 weeks of storage, the fillets were rehydrated and desalted. Changes in weight and chemical content were followed through the process. The addition of polyphosphates resulted in poorer quality, when considering the entire process, although differences were not observed in sensory evaluation after rehydration and steam boiling. Improvements in yield were observed in the fillets containing polyphosphate, after dry-salting and storage (P < 0.05). However, the increase in weight during rehydration was far less by those fillets than by the control group, where no phosphate was used.     

Effect of Brining, Modified Atmosphere Packaging, and Superchilling on the Shelf Life of Cod (Gadus morhua) Loins

ABSTRACT:  The aim of these experiments was to evaluate the effect of brining, modified atmosphere packaging (MAP), and superchilling on the quality changes of cod loins as measured by microbial, sensory, and chemical analysis. Unbrined and brined (2.5 ± 1.0% NaCl) cod loins were kept in styrofoam boxes (air) and under modified atmosphere (MA, CO₂/O₂/N₂: 50/5/45) at 0, −2, and −3.6 °C. Samples were examined over a 4-wk period. Total viable psychrotrophic counts and counts of H₂S-producing bacteria reached higher numbers in the air-packed brined fish at −2 and −3.6 °C than in comparable unbrined groups, being significantly different ( P  < 0.05) at the lower temperature. However, lower counts of these bacteria were obtained in the brined MAP fish than in comparable unbrined fish. Counts of  Photobacterium phosphoreum  increased most rapidly in air- and MA-packed loins kept at 0 °C. Lower counts were found at superchilled temperatures. According to sensory analysis the shelf life of unbrined air-packed loins was about 11 d at 0 °C and 14 to 15 d at −2 °C. The shelf life of MA-packed unbrined loins was about 14 to 15 d at 0 °C but 21 d at −2 °C. Thus, synergism of combined superchilling (−2 °C) and MA led to a considerable shelf life increase for unbrined loins despite the fact that processing and packaging took place 4 to 5 d post-catch. The shelf life of air-packed brined loins at −2 °C was 12 to 15 d but only 13 d under MA. The same synergistic effect did therefore not apply to brined loins as with unbrined ones.     

Variability of Salt Absorption by Brine Dipped Fillets of Cod (Gadus morhua), Blackback Flounder (Pseudopleuronectes americanus), and Ocean Perch (Sebastes marinus)

Major changes in sodium content of fillets of cod, blackback flounder, and ocean perch resulted from varying concentration of brine solution (5, 10, or 15%), duration of dip (30, 60 or 90 sec), fillet thickness, season of catch, and rinsing or skinning fillets before cooking. Postmortem age (1-5 days) of fish, temperature of brine solution (6, 12, or 20°C), and cooking had minor effects on final sodium concentration.