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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. [ABSTRACT FROM AUTHOR]

Two different harvest procedures were employed to investigate whether the method of harvest has an effect upon deteriorative processes that occur during the frozen storage of Chinook salmon ( Oncorhynchus tshawytscha) white muscle tissue. These 2 harvest methods, termed “rested”—involving sedation with the aquatic anesthetic AQUI-S™ and “exercised”—a simulated conventional harvest not involving sedation, contrasted levels of activity of the animal prior to and upon slaughter. Rested and exercised harvesting protocols produced tissue in significantly different postmortem physiological states prior to freezing. Rested, postharvest tissue maintained high metabolic energy stores of ATP and glycogen within the tissue, with low concentrations of tissue and plasma lactate. Exercised tissue exhibited near depleted concentrations of ATP and glycogen and a marked lactate accumulation. In both treatments, no significant change in metabolite levels was seen over a 6-mo storage period at −19 °C when tissue was frozen immediately postharvest. Transfer of tissue from frozen temperatures (−80 and −19 °C), to refrigerated (−1 and +4 °C, respectively) resulted in rapid glycolysis, depleting tissue ATP and glycogen stores and increasing tissue lactate concentrations. Metabolic activity was more significant in rested tissue owing to the larger concentrations of metabolic energy stores and occurred at temperatures between −3 and −1.5 °C. During frozen storage (−19 °C), there was an increase in the secondary lipid oxidation product TBARS, but harvest treatment had no effect. However, following transfer from frozen to refrigerated (+4 and −1 °C) storage, rested tissue showed a significant ability to retard the development of TBARS products. [ABSTRACT FROM AUTHOR]

Frozen fish usually have a much lower market price than fresh fish; therefore, adulteration could occur. This article focuses on the use of near infrared (NIR) spectroscopy to detect whether fish has been frozen-thawed because NIR spectroscopy has demonstrated the potential for addressing some authenticity issue in foods and is known to be a nondestructive rapid technique. Horse mackerel ( n = 162) were evaluated as fresh and frozen-thawed fish sample. Dry extract spectroscopy by infrared reflection (DESIR) of fresh and frozen-thawed fish samples was performed on the meat juices then discriminated by principal component analysis (PCA) and multiple linear regressions (MLR). In DESIR spectra, the overall absorbance level was found to decrease in frozen-thawed samples, indicating the different chemical composition of juice, amount of dry matter, particle size, and their scattering properties. The spectral changes that take place between fresh and frozen-thawed samples are clearly seen in the 1920- to 2350-nm region. The spectra are dominated by peaks attributed to proteins, in particular, peaks at 1510, 1700, 1738, 2056, 2176, 2298, and 2346 nm. It was found that fresh and frozen-thawed fish could be separated 100% correctly by DESIR technique. [ABSTRACT FROM AUTHOR]

This article discusses a study of the effect of delayed icing on the bacteriological quality of the barracuda (Sphyraena barracuda). Tests on the commercially important tropical fish used samples obtained from the fish-landing center in Tuticorin, India, which were segregated into two lots. One lot (II) was iced immediately while the other lot (DI) was kept at room temperature before being iced. Results revealed that the 6-hour delay in the icing of the fish reduced the shelf life of iced fish.

The article presents information on a study which determined how freezing prior and/or following smoking affected central quality characteristics of the finished cold-smoked Atlantic salmon, Salmo salar. A review of the related literature on cold-smoked salmon is given. Findings showed that freezing prior smoking resulted in increased product yield and water content, but softer texture and increased K-value. However, refreezing the finished products had little effect on quality.

A quality index method (QIM) consisting of 9 parameters with a total of 17 sensory points was developed for frozen hake (M. capensis and M. paradoxus). The score sheet was divided into 2 parts. The 1st, including 7 parameters with up to 13 sensory points, was directly related to loss of quality during storage at -20 °C. Multivariate analysis confirmed the relevance of these parameters for prediction of storage time. The 2nd part contained 2 additional parameters scoring up to 4 sensory points. These parameters are commercially important but not directly linked to storage time. [ABSTRACT FROM AUTHOR]

The objective was to evaluate the suitability of sea-frozen, thawed cod fillets for the "chilled" seafood market. Fillets were kept frozen for 17 mo. After thawing, fillets were kept iced and at 4 °C. Microbiological research on fillets showed higher initial numbers in post-rigor than pre-rigor fillets. Pre-rigor fillets were judged fresher after 2 mo of storage compared to post-rigor. With longer freezer storage, lower initial freshness scores were obtained, and formation of trimethylamine in thawed fillets was slowed. Thawed fillets frozen prior to rigor merited higher scores for freshness than fillets frozen post-rigor. This difference decreased with prolonged freezer storage. The results strongly indicate that Fillets should be frozen pre-rigor. [ABSTRACT FROM AUTHOR]

Presents the chemical and visual analyses of fresh albacore tuna that were frozen and stored at -18 degrees centigrade and -25 degrees centigrade for one year. Analyses carried out at 1, 3, 6, 9, and 12 month storage; Low loss of moisture at -18 degrees centigrade; Slight reduction of total volatile basic nitrogen at -25 degrees centigrade.

Presents a study which examined the structural changes in cod myosin after formaldehyde (FA) addition with and without subsequent freezing at -18 degrees Celsius by Raman spectroscopy, ANS hydrophobicity, solubility and SDS-PAGE profiles. Study methodology; What the SDS-PAGE showed; Indications of Raman spectral analysis; Findings of study; Concluding remarks.

The article examines the effect of thawing, refreezing and frozen storage on the quality of muscle functionality and sensory properties of cod fillet. Based on the results, thawed and refrozen fish muscle showed a faster decline in myofibril protein solubility and reduced water-holding capacity. Furthermore, long thawing times before re-freezing resulted in cooked fish with more gray appearance and more bad taste.

BSTRACT The quality changes during frozen storage of two underutilized species of fish: mackerel ( Scomber scombrus), a fatty species, and white hake ( Urophycis tenuis) a nonfatty, gadoid species, with or without a bag, vacuum, and/or erythorbic acid, were measured using the dimethy-lamine (DMA) test for hake and the thiobarbituric acid (TBA) test for mackerel, and by Instron deformation, expressible moisture, thaw drip, cook loss, and sensory evaluation for both species. Texture deterioration and lipid oxidation limited the shelf-life of hake and mackerel, respectively. Air (oxygen) prolonged the shelf-life of hake but lessened that of mackerel. Erythorbic acid accelerated the rate of texture deterioration in hake but inhibited the rate of lipid oxidation in mackerel. [ABSTRACT FROM AUTHOR]

BSTRACT Six New England marine species, yellowtail flounder ( Limanda ferruginea), whiting ( Merluccius bilinearis), scup ( Stenotomus chrysops), butterfish ( Peprilus triacanthus), mackerel ( Scomber scombrus) and herring ( Clupea harenqus), were stored on ice whole, dressed or skin-on fillets and tested for freshness using the GR Torrymeter. Whole forms of flounder, whiting, scup and butterfish were examined for odor and general appearance. Torrymeter variability and linear relationships during the storage period were established. While the total pattern of Torrymeter decline followed a polynomial regression, quality curves had linear portions with significant correlation coefficients up to 7-8 days of storage. The rate of deterioration of fatty fish was faster than for flounder or scup. A significant linear correlation existed between sensory data and Torrymeter values. [ABSTRACT FROM AUTHOR]

BSTRACT Formaldehyde at concentrations occurring in frozen fish increased the extent of denaturation as measured by loss in solubility, decrease in ATPase activity and increase in surface hydrophobicity, of partially purified cod myosin stored at -25°C or -80°C. Most denaturation occurred during the freezing/thawing process. Formaldehyde caused some crosslinking of myosin, but crosslinking and insolubilization appeared to be relatively independent. The presence of diamines led to some increase in crosslinking but had little effect on protein solubility. [ABSTRACT FROM AUTHOR]

Studies the effect of two treatments to decrease fish temperature after glazing (refreezing) on muscle tissue of cod and rainbow trout. Rainbow trout marker enzyme activity; Effects of fast refreezing after glazing; Refreezing time for cod and rainbow trout; Leakage of intracellular marker enzyme activity.

BSTRACT A fluorometric method and a rapid paper test method were developed for differentiating fresh from frozen-thawed fish. The methods were based on measurement of the activity of neutral β-N-acetylglucosa-minidase. This enzyme, found in fish red blood cells, was inactive in intact cells but was activated when cells were disrupted by freezing and thawing. Both methods were applicable for testing most common edible fish prior to filleting and required about 20 min using a UV-lamp. [ABSTRACT FROM AUTHOR]

BSTRACT During frozen storage, minced cod and ocean perch were examined by expressible moisture (EM), water binding potential (WBP) and computerized texture profile analysis (TPA). The results suggested that a microcomputer interfaced with the Instron efficiently performed TPA. The texture and water loss of all fish minces changed more rapidly at -7°C storage than at -20°C and -40°C. Furthermore, cod, a gadoid with the ability to degrade trimethylamine oxide to dimethylamine and formaldehyde, deteriorated faster than ocean perch, which did not have this ability. EM was useful for examining the water loss of frozen fish at - 7°C only during the first two weeks of storage. The WBP at -7°C storage showed a good correlation with storage time for cod and ocean perch. This suggests that WBP might be a good indicator for examining water holding ability of fish proteins. [ABSTRACT FROM AUTHOR]

Textural quality of quick frozen and conventionally frozen whole crayfish was evaluated. Toughness, as measured by Kramer shear press, increased significantly (p ≤ 0.05) as a result of freezing. Between 6 and 16 wk of frozen storage, toughness increased (p I 0.05) in seasoned (SCF) samples but remained the same in all other treatments. In all treatments, toughness declined after 16 wk of frozen storage. Individually quick frozen (IQF) samples were more tender ( p ≤ 0.05) than conventionally frozen (CF) samples. Seasoned crayfish had the greatest degree of toughness (p ≤ 0.05). Extractable protein decreased (p ≤ 0.05) during frozen storage, with IQF samples showing the smallest changes. SCF samples had significantly (p ≤ 0.05) lower moisture retention and more (p ≤ 0.05) lipid oxidation. [ABSTRACT FROM AUTHOR]

BSTRACT Postmortem formation of 5′-inosine monophosphate, inosine and hypoxanthine in Pacific cod and pollock fillets during chilled storage was monitored over a two week period. Accumulation of hypoxanthine in Pacific cod ( Gadus macrocephalus) fillets proceeded more slowly than has been reported for Atlantic cod ( Gadus morhua) but similar to North Sea cod ( Gadus callarias L.). For both both cod and pollock, hypoxanthine was negatively correlated with flavor and desirability (p < 0.01), while both inosine and 5′-inosine monophosphate were positively correlated with overall desirability (p < 0.01). [ABSTRACT FROM AUTHOR]

The aim of this work was to evaluate the effects of freezing and frozen storage at –24 °C on the quality of Icelandic herring fillets, focusing on protein solubility and viscosity at pH 2.7 and 11 used for pH-aided protein isolation. The evaluation of quality was based on chemical analyses, protein degradation measurements, and changes in protein solubility and viscosity at pH 2.7 and 11 after up to 6-mo frozen storage of the herring fillets. Lipid oxidation measured as TBARS values increased significantly during the frozen storage ( P < 0.05). Protein solubility at pH 2.7 decreased during frozen storage for 6 mo, where the solubility was about 10% lower after 6-mo frozen storage compared to the beginning ( P < 0.05). At pH 11, the solubility became approximately 15% lower after 6-mo frozen storage compared to initial solubility ( P < 0.05). Viscosity, measured at pH 2.7, increased after 3 mo of frozen storage ( P < 0.05). At pH 11, the viscosity increased significantly after 1-wk frozen storage, compared to fresh herring fillets, but did not increase significantly with further storage ( P < 0.05). Changes found in solubility and viscosity indicated protein degradation due to freezing and frozen storage. SDS-PAGE analysis did not reveal any protein cross-linking or aggregation formation, either with frozen storage or due to exposure to low pH. [ABSTRACT FROM AUTHOR]