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.     

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.     

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.     

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.     

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.     

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.     

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.     

Frozen Storage Quality of Rainbow Trout (Oncorhynchus mykiss) as Affected by Oxygen, Illumination, and Fillet Pigment

We investigated the influence of packaging materials with high, medium and low oxygen transmission rates (OTR) on the development of 2-thiobarbituric acid-reactive substances (TBARS) and astaxanthin retention in rainbow trout fillets. Three different levels of astaxanthin, during dark or illuminated frozen storage were studied. Samples were analyzed after 17, 29 and 36 wk frozen storage. Rancidity developed more rapidly in packages with high OTR. This effect was more pronounced in illuminated samples, also verified by sensory evaluation. Fillets with highest astaxanthin content reached maximum TBARS after 29 wk. The two less pigmented sample groups reached maximum after 17 wk frozen storage, indicating antioxidative effects of astaxanthin.     

Effect of Methodology on Total Volatile Basic Nitrogen (TVB-N) Determination as an Index of Quality of Fresh Atlantic Cod (Gadus morhua)

Six different published methods of determining TVB-N were evaluated for accuracy, precision, suitability as an index of quality, and both cost and speed of determination, using gutted Atlantic cod stored in ice for up to 18 days. Although the method of determination affected the actual values obtained, it did not affect the overall relationship between TVB-N and sensory assessment of raw or cooked fish. The method of determination also affected precision and both cost and speed of determination. If high operational costs could be tolerated, MgSO₄ ext/steam distillation would be the preferred method but if variability of results could be tolerated, TCA extraction/steam distillation would be the method of choice.     

Processing and Frozen Storage Effects on the Iron Content of Cod and Mackerel

Processing and subsequent frozen storage affected the iron content of cod (Gadus morhua) and mackerel (Scomber scombrus) muscle tissue. Frame mince was obtained from the bone rack, without the head or viscera remaining, after filleting. Frame mince had significantly higher iron levels than intact fillets with or without skin or fillets that were subsequently minced. Skin-on fillets had more iron than skin-off fillets. Cod frame mince had about 50% heme iron, while mackerel frame mince ranged from 20-64%. Nonheme iron increased during frozen storage due to heme breakdown. Storage above ?14°C was more deleterious to the heme molecule than lower temperatures (?20°C or ?40°C).     

Lipid and autoxidative changes in cold stored cod (Gadus morhua)

A study of lipid changes during the frozen storage of cod confirms that the major change is that of lipolysis. Oxidation is extremely slow and occurs primarily in the phospholipid fraction. Nevertheless, sufficient oxidation takes place during cold storage to reduce the acceptability of the fish primarily through the production of hept-cis-4-enal. The mechanism whereby hept-cis-4-enal occurs is discussed.     

Properties of actomyosin isolated from cod (Gadus morhua) after various periods of storage in ice

Natural actomyosin was isolated from cod (Gadus morhua L) stored in ice for up to 28 days. The gelling properties, apparent viscosity, Ca^2--ATPase activity and component protein composition by sodium dodecyl sulphate (SDS) electrophoresis were determined for each preparation of natural actomyosin. The apparent viscosity, protease activity, trimethylamine (TMA) content and pH of the fish muscle were also determined. The results showed that the apparent viscosity and Ca^2--ATPase activity tended to decrease slightly during ageing of the fish in ice, whereas some of the gelling properties showed a maximum between 3 and 6 days of storage. However, there was no change in the apparent viscosity of the muscle as a whole even after the fish were considered to be stale according to the TMA values. The ratio of myosin heavy chain to actin in the actomyosin changed with the time of storage of the fish, being highest at 3 days when gelling properties were maximal and decreasing progressively thereafter.     

Instrument for Nondestructive Texture Measurement of Raw Atlantic Cod (Gadus Morhua) Fillets

A portable instrument was developed to rapidly and objectively determine texture (firmness and resilience) of raw Atlantic cod (Gadus morhua) fillets. A controlled study determined the texture of raw fillets from 774 cod, caught at three different times of year. Compared to texture grades of fillets assessed by trained and experienced Fish Inspection Officers, this instrument was a dependable method of rapidly determined texture of raw fillets.     

Microbial and sensory changes during refrigerated storage of desalted cod (Gadus morhua) preserved by combined methods

Water blanching and the use of additives (potassium sorbate and citric acid) combined with different types of packaging (air, vacuum "VP" and modified atmosphere packaging "MAP": 60% CO(2), 30% N(2) and 10% O(2)), were studied as new methods of preservation of chilled desalted cod. Microbial counts and total volatile basic nitrogen (TVB-N) analyses were carried out during a period of 42 days on all samples stored at 4 degrees C. No Aeromonas or sulphite-reducing Clostridium were isolated from any of the analysed samples. The lowest microbial counts of mesophilic, psychrotrophic, Pseudomonas, moulds and yeasts, were found in samples with additives in all kinds of packaging. These samples in VP or MAP maintained an excellent microbial quality throughout the 42 days of storage, with mesophilic and psychrotrophic counts always below 4 log CFU/g. Counts of the four microorganisms above-mentioned in blanched samples packaged with air, exceeded 5 log CFU/g on days 21-28, so it became necessary to use VP or MAP to maintain these microorganisms at an acceptable level for the entire storage period. TVB-N contents were low in samples with additives, regardless of the kind of packaging, as well as in blanched samples packaged in VP and MAP, never reaching 25 mg/100 g. Since there were no significant differences either in microbial growth or in TVB-N between samples in VP and MAP, a sensory analysis was performed only in desalted cod submitted to the two treatments (blanching and additives) combined with VP, both in raw and cooked samples. The results of this analysis showed that the addition of potassium sorbate and citric acid did not alter the typical organoleptic features of desalted cod. The sensory characteristics of both blanched samples and those with additives in VP showed no change during the period of the study.