Detection of frozen-thawed salmon (Salmo salar) by a rapid low-cost method

The aim of this study was to evaluate a rapid low-cost system based on impedance spectroscopy as an alternative method to differentiate between fresh and frozen-thawed salmon. Samples of fresh salmon and others submitted to freezing at −18 °C or to 2 freezing cycles, kept in frozen storage for different times, were analysed. In general, no significant differences in moisture, total volatile basic nitrogen, pH, texture parameters, K₁ value, or microbial counts between the different samples were observed. This revealed that the freezing process, storage time or number of freezing cycles did not affect the physico-chemical parameters of fish samples, except for water holding capacity, which was significantly lower in all frozen samples compared with fresh salmon. The results showed that impedance spectroscopy was unable to differentiate between different storage times under frozen conditions; however, this technique could be a useful tool to detect fish submitted to freezing process.     

Survey of Clostridium difficile in retail seafood in College Station,Texas

The incidence and severity of disease associated with toxigenic Clostridium difficile have increased in hospitals in North America with the emergence of newer, more virulent strains. Toxigenic C. difficile has been isolated from food animals and retail meat with potential implications of transfer to humans. The objective of the present study was to investigate the prevalence of C. difficile in retail seafood from grocery stores in College Station, Texas. C. difficile was found in 4.5% (3/67) of shellfish and finfish samples. The positive samples included one each from fresh mussel, frozen salmon and frozen shrimp. The mussel and salmon isolates were characterized as toxinotype V and pulsed-field gel electrophoresis (PFGE) type-NAP7. The shrimp isolate was identified as toxinotype XII, but had an unknown PFGE type. Susceptibilities to 11 antimicrobial agents were identical for the mussel and salmon isolates and were sensitive to eight of 11 antimicrobials (including ampicillin) and intermediate to clindamycin. However, the shrimp isolate was resistant to clindamycin and ampicillin. This study demonstrates that seafood, like other food commodities, can be contaminated by C. difficile.     

Differentiation of fresh and frozen/thawed fish, European sea bass (Dicentrarchus labrax), gilthead seabream (Sparus aurata), cod (Gadus morhua) and salmon (Salmo salar), using volatile compounds by SPME/GC/MS

BACKGROUND: A simple method based on solid phase microextraction/gas chromatography/mass spectrometry (SPME/GC/MS) was applied for studying the volatile profiles of whole fish samples of European sea bass (Dicentrarchus labrax) and gilthead seabream (Sparus aurata) and fillets of cod (Gadus morhua) and salmon (Salmo salar) during frozen storage in order to be able to differentiate a fresh product from one that has been frozen. Analysis of volatile compounds was performed on these two product types, fresh and after freezing/thawing following storage at ? 20 °C for 30 and 90 days. RESULTS: More than a hundred volatile compounds were found by SPME/GC/MS. Statistical processing by principal component analysis and ascending hierarchical classification was used to classify the samples into categories and verify the possibility of separating fresh samples from those that had been frozen and thawed. The compounds to be used as differentiators were identified. Four compounds were common to all species: dimethyl sulfide, 3‐methylbutanal, ethyl acetate and 2‐methylbutanal. Not only were they found in larger quantities after thawing but they also increased with the duration of storage at ? 20 °C. CONCLUSION: These four compounds can therefore be considered as potential markers of differentiation between a fresh product and one that has been frozen. Copyright © 2012 Society of Chemical Industry     

Consumer willingness to pay for quality attributes of fresh seafood: A labeled latent class model

We applied a labeled choice experiment (LCE) to investigate consumer demand and choice behavior for fresh seafood in a retail market. The LCE was conducted for a large number of seafood alternatives (i.e., seafood species) labeled by the respective seafood name (e.g., cod, salmon, mussels). Consumer heterogeneity in preference was expressed by estimating a labeled latent class model with alternative-specific effects, which varies choice probability and model parameters over seafood alternatives and across classes. The willingness to pay (WTP) for extrinsic attributes (e.g., product form, production method, and country of origin), and the rank ordered-intrinsic value were estimated for each seafood alternative within classes and the entire market. The WTP estimate in our study is expected to be more accurate than those derived from studies based on single product alternatives because the LCE allows respondents to evaluate choice alternatives through both attribute judgment and alternative comparison. Exploring a variety of product alternatives is also meaningful to firms with multiple products (e.g., fresh seafood retailers) or firms with many direct competitors.     

基于高通量测序的紫贻贝中微生物群落分析

为探究不同状态下紫贻贝制品表面附着的微生物菌群组成情况。本实验以新鲜紫贻贝、冻藏紫贻贝、自制紫贻贝干,贮藏自制紫贻贝干和市售紫贻贝干为研究对象,通过对紫贻贝表面附着微生物提取及高通量测序分析,获得不同紫贻贝样品中微生物组成及变化情况。实验结果表明,各样本中有效序列范围为30066～40563条、Operational taxonomic unit(OTU)范围为28～128,其中市售紫贻贝干OTU数最低,而冻藏紫贻贝OTU数相对较高;新鲜紫贻贝和自制紫贻贝干中主要是嗜冷杆菌属和不动杆菌属,冻藏紫贻贝干中主要为嗜冷杆菌属,贮藏紫贻贝干中主要为假单胞菌属和嗜甲基菌属,而市售紫贻贝干中优势菌群为葡萄球菌属和肠球菌属。不同状态下的紫贻贝样品的菌群组成均存在着较大距离,表明紫贻贝状态、加工过程及贮藏销售环境等,均对贻贝产品菌群组成产生较大的影响。研究结果可为保障紫贻贝制品的质量与安全提供参考。     

Effects of microbial transglutaminase added edible coatings based on heated or ultrasound-treated whey proteins in physical and chemical parameters of frozen Atlantic salmon (Salmo salar)

The effects of the addition of transglutaminase to heated or ultrasound-treated whey protein coatings on quality parameters of frozen Atlantic salmon (Salmo salar) were evaluated. The influence of the type of denaturation treatment (heating or sonication) was also studied. The addition of microbial transglutaminase to the coatings did not significantly modify the yields, drip losses, colour and chemical composition of the fish fillets. The yields were higher in the samples protected with heated coatings than in those with ultrasound-treated ones. Transglutaminase addition to heated whey protein coatings delayed lipid oxidation. Ultrasound-treated coatings with or without enzyme addition were equally effective for lipid oxidation reduction after frozen storage of Atlantic salmon than heated-treated transglutaminase-added coatings.     

Potential applications of high pressure for improvement in salmon quality

Cold-smoked salmon is an important value added, ready-to-eat food. Quality issues associated with cold-smoked salmon are examined. Effects of smoking, drying, enzymatic spoilage, feed usage, textural and biochemical changes during frozen storage of cold-smoked salmon are described. Important pathogens associated with cold-smoked salmon, such as Listeria monocytogenes and other spoilage organisms are also described and potential areas for further research are identified. Recent advances in the application of high pressure processing to seafood safety and quality improvement are discussed and the potential of this technology to improve the quality of cold-smoked fish from farmed Atlantic salmon is outlined.     

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.     

Effects of mechanical handling,storage on ice and ascorbic acid treatment on lipid oxidation in cultured Newfoundland blue mussel (Mytilus edulis)

Lipid oxidation of cultured blue mussels (Mytilus edulis) during mechanical handling and storage on ice was investigated. Furthermore, the exposure of blue mussels to ascorbic acid (Asc) as an antioxidant and its effects on lipid oxidation of sample was monitored. Thiobarbituric acid reactive substances (TBARS) of stored mussels were significantly (p < 0.05) higher than those of the fresh mussels. Mechanical handling of mussels, which includes washing, sorting and packaging, for up to 1 h did not affect their oxidative status significantly (p < 0.05). Furthermore, exposing live mussels to specific concentrations of Asc retarded lipid oxidation significantly (p < 0.05) during storage on ice for only 5 days, after which the Asc became a pro-oxidant.     

Consumer acceptability of cod and whiting after chilled storage and freezing and thawing

The effect of freezing and thawing, and of storage at 0°C on the acceptability of two white fish species (cod and whiting) was investigated. It was concluded that samples which had been frozen and thawed were no less acceptable than fresh samples and that storage of fresh fish at 0°C produced a linear decline in overall acceptability of both species. A method of presenting the data to allow decisions to be taken on the shelf life of chilled products is discussed.     

Effect of processing treatments (frozen,frying) on contents of minerals in tissues of ‘frutti di mare’

The objective of this study was to determine the effect of thermal treatment (frying) of frozen seafood on the content of minerals and heavy metals. An analysis was conducted to compare concentration of sodium, magnesium, potassium, calcium, copper, iron, manganese, zinc, as well as lead, cadmium and mercury in the analysed tissues of invertebrates (shellfish – blue mussel, Japanese squid, white shrimp and octopus). Thermal processing (in this case, frying) applied to the frozen invertebrates was found to affect significantly the content of macro‐ and microelements as well as the content of heavy metals, except for potassium and manganese content in mussels and shrimps, respectively. Frozen and thermally treated (frying) mussels are characterised by significantly higher concentrations of the analysed minerals (except Na⁺, Ca⁺², Cu⁺²), as well as higher concentrations of cadmium and mercury. In turn, shrimps and squids are invertebrates with lower content of both macro‐ and microelements.     

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.     

不同贮存及加工条件对海产品中组胺与TVBN的影响

测定了3种海产品在冷藏、室温等条件下储藏或放置期间组胺与挥发性盐基氮(TVBN)含量的变化,比较了各海产品在上述条件下其品质的劣变与组胺含量之间关系.同时,还比较了3种海产品在水煮和油炸处理前后组胺的含量变化.结果显示:冻藏是海产品较为理想储藏方法,其组胺含量增加缓慢,品质的劣变不明显;水煮和油炸都能够在一定程度上较少鱼肉中的组胺含量,水煮处理效果优于油炸处理.     

冷冻调理贻贝的加工工艺

通过对冷冻调理贻贝加工工艺参数的筛选试验,确定了冷冻调理贻贝的调味料配方、浆液浓度、食用时油炸温度及油炸时间等工艺参数。经分析检测,在-18℃下冻藏6个月后,冷冻调理贻贝仍符合卫生质量要求。     

Whey protein-based coatings on frozen Atlantic salmon (Salmo salar): Influence of the plasticiser and the moment of coating on quality preservation

The effects of different whey protein concentrate coating formulations (with or without glycerol or sorbitol in two proportions) on frozen Atlantic salmon quality parameters were evaluated. The influence of the moment of coating application (before or after freezing) was also studied. The coating application after freezing increased the thaw yield, decreased the drip loss, and modified colour parameters of frozen and thawed fillets, in comparison with application before freezing. The moment of coating also influenced the colour of cooked fish fillets. The type of plasticiser affects the colour of thawed and cooked samples, but not the colour of frozen samples. The protein coatings delayed lipid oxidation of salmon fillets, providing better protection against it than water glazing, and this effect was more pronounced when glycerol instead of sorbitol was used in the coating formulation.     

Effect of Fish and Oil Nature on Frying Process and Nutritional Product Quality

ABSTRACT: The modifications on a lean fish (cod—Gadus morhua) and a fatty fish (farmed salmon—Salmo salar) after the application of pan-frying using 2 types of oil with different lipid profile (extra virgin olive oil and sunflower oil) was the aim of this study. Fat content and total energetic value increased significantly after the frying process only in the lean fish, without relevant changes in the fatty fish. Extra virgin olive oil led to a higher fat absorption rate than sunflower oil in both fish. Frying hardly affected the lipid profile of farmed salmon regardless the oil used, however it drastically changed in fried cod compared to raw cod. Omega-6/omega-3 ratio increased from 0.08 in raw cod to 1.01 and 6.63 in fried cod with olive oil and sunflower oil, respectively. In farmed salmon, the omega-6/omega-3 ratio was 0.38 (raw), and 0.39 to 0.58 in fried salmon. The amount of EPA + DHA slightly decreased with frying in salmon, and increased in cod. The type of oil has more influence in the nutritional fish quality for the lean fish compared to that of the fatty fish. The use of extra virgin olive oil was efficient to avoid a significant increase of the lipid oxidation intensity during frying in cod but not in salmon. Practical Application: Food modifies its composition and nutritional value with the application of cooking technologies. As most food table composition tables are based on raw food products, this article contributes with interesting data on pan-fried fish composition, which may improve the approach to achieve a real intake of healthy nutrients as omega 3 fatty acids.     

Comparative Rates of IMP Degradation in Unfrozen and Frozen-and-Thawed (Slacked) Fish

SUMMARY— The comparative rates of IMP degradation between fresh and frozen-and-thawed (slacked) fish were compared on six different species of fish. Several factors that could contribute to a rate change of IMP degradation were evaluated. These included freezing temperatures, time in frozen storage, pre- and post-rigor freezing, and method of killing the fish.
English sole and rainbow trout showed slight increases in the rate of IMP degradation when they were frozen and then thawed within 48 hr. Silver salmon and halibut that were frozen and then thawed within 48 hr showed no change in the rate of IMP degradation. Halibut, however, that was frozen and stored at −20°F for 3 months showed a slight decrease in the rate of IMP degradation after it was thawed; but king salmon handled under the same conditions did not.
The method of kill or freezing the fish either pre- or post-rigor did not alter the rate of IMP degradation after the fish was thawed.
No loss of IMP occurred in fish (halibut) stored at −20°F. Over one-third of the original IMP content was lost in halibut stored at +15°F after 3 months of storage.
These results show that there is no significant difference in the rate of IMP degradation between fresh and slacked fish. The flavor-contributing effect of IMP in slacked fish therefore should be the same as in fresh fish, provided the fish was frozen and stored at or near a temperature of −20°F.     

Effect of freezing method and frozen storage duration on instrumental quality of lamb throughout display

This study evaluated the effect of freezing method (FM) (air blast freezer, freezing tunnel, or nitrogen chamber) and frozen storage duration (FSD) (1, 3, or 6 months) on the instrumental measurements of quality of thawed lamb, aged for a total of 72 h, throughout a 10-d display period, compared to the quality of fresh meat. pH, colour, lipid oxidation, thawing, and cooking losses in Longissimus thoracis and lumborum muscle, were determined following standard methods. FM affected yellowness, FSD redness and thawing losses, and both affected oxidation (increased as freezing rate decreased and/or as storage duration increased). When compared with fresh meat, the main differences appeared on oxidation (where a significant interaction between treatment (3FM × 3FSD + fresh meat) with display duration was detected), and on total losses (thaw + cook losses). Oxidation was lower in fresh meat, but values were not significantly different from those stored frozen for 1 month. Fresh meat had smaller total losses than did thawed meat, but losses were not significantly different from meat frozen in the freezing tunnel and stored frozen for 1 month. Display duration had a greater effect on instrumental quality parameters than did FM or FSD. pH, b*, and oxidation increased, and L* and a* decreased with an increase in the number of days on display. In conclusion, neither freezing method nor frozen storage up to 6 months influenced extensively the properties of lamb when instrumental measurements of quality were measured in meat that had been displayed for 1 d after thawing. The small deterioration shown in this study should not give consumers concerns about frozen meat.     

Mercury, arsenic, lead and cadmium in fish and shellfish from the Adriatic Sea

The aim was to measure concentrations of total mercury, total arsenic, lead and cadmium in common edible fresh fish and shellfish from various areas of the Adriatic Sea. Estimates of intake of these elements were made through seafood consumption by the general population. Samples were either wet digested for mercury and arsenic, or dry ashed for lead and cadmium analysis. Mercury was measured by cold vapour atomic absorption spectrometry (CV AAS) and arsenic, lead and cadmium by electrothermal atomic absorption spectrometry (ET AAS). Quality control procedures of analytical methods, which included analyses of dogfish muscle-certified reference material DORM-2, confirmed the acceptability of methods. The highest mercury and arsenic concentrations were found in hake ( Merluccius merluccius ) and the lowest in mackerel ( Scomber scombrus ). The respective values in hake were 0.373 ±0.075 and 23.3 ±3.6, and in mackerel 0.153 ±0.028 and 1.06 ±0.29 mg kg -1 fresh weight (mean ±SD). Lead and cadmium concentrations were about 10 times higher in shellfish than in analysed fish. The highest lead and cadmium concentrations were found in mussel ( Mytilus galloprovincialis ) and the lowest in hake. Respective lead and cadmium values in mussel were 0.150 ±0.009 and 0.142 ±0.017, and in hake were 0.007 ±0.004 and 0.002 ±0.001 mg kg -1 fresh weight. The concentrations of analysed elements were below acceptable levels for human consumption set by the Croatian Ministry of Health, except for total arsenic. The estimated intake of those trace elements included in this study through seafood consumption by the general population did not exceed the provisional tolerable weekly intake recommended by the Joint FAO/WHO Expert Committee on Food Additives.     

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.