Textural Properties of Raw Salmon Fillets as Related to Sampling Method

Textural properties of raw Atlantic salmon (Salmo salar) fillets from different origin were studied on different locations of the fillets. Three instrumental methods were applied for evaluation of textural properties. Two methods were based on puncture tests, using flat-ended cylinder or spherical probes measuring the hardness of the fillet. The third method was based on cutting the fillet with a blade and measuring the shear force. Hardness and shear force increased from head to tail, and the location below the dorsal fin was found to be most reliable. The shear force method was found to be more sensitive than the puncture methods and best suited for practical application.     

Atlantic salmon (Salmo salar,L) as raw material for the smoking industry. II: Effect of different smoking methods on losses of nutrients and on the oxidation of lipids

The changes in total fat content, fatty acid composition, tocopherol, ascorbic acid, pH and oxidation were analysed in Atlantic salmon (Salmo salar, L.) in response to either cold smoking (20 or 30 °C) or electrostatic smoking. Both fresh and frozen fillets were dry-salted before smoking. The fish smoked were the lean ocean-ranched salmon caught off Iceland in June 1998 and farmed Norwegian salmon, slaughtered in either November 1998 or April 1999, differing in fresh fillet fat content from 84 to 169 g·kg⁻¹ wet weight. The fresh material used in smoking significantly affected the smoking loss of nutritive components in the fillets. The leaner the fish the higher percentile loss in fillet fat. Ascorbic acid decreased about 80 percent from the fresh value, independent of smoking temperature (20 or 30 °C). The fish that were dry-salted and electrostatically smoked only lost about 10 percent of the fresh ascorbic acid content, independent of the type of raw material used, indicating a conserving effect on ascorbic acid by the electrostatic process. Also, the electrostatically smoked fish showed a smaller drop in fillet pH than cold-smoked fillets, while tocopherol was little affected by the smoking methods tested.     

Effect of dietary levels of fat, α-tocopherol and astaxanthin on colour and lipid oxidation during storage of frozen rainbow trout (Oncorhynchus mykiss) and during chill storage of smoked trout

 Female rainbow trout (Oncorhynchus mykiss) with an initial weight of 0.8–0.9 kg were raised in two experiments including a total of 2550 fish divided into 17 groups. The fish were raised for 6 months on 13 different feeds (four fish groups were replicates) varying in dietary levels of fat (27% or 32%), astaxanthin (40, 70 or 100 mg astaxanthin/kg feed) and vitamin E (α-tocopherol; 100, 300 or 600 mg all-rac-α-tocopheryl acetate/kg feed). The levels of fat, astaxanthin and α-tocopherol in the fillets all increased with increasing dietary levels of each feed component. Furthermore, astaxanthin deposition was found to be significantly improved by increasing the dietary fat level from 27% to 32%, but was not affected by dietary levels of α-tocopherol. The highest deposition of α-tocopherol was found in fish fed the lowest level of astaxanthin (40 mg/kg), whereas α-tocopherol deposition was unaffected by the dietary fat level. Frozen storage (–28  °C) of gutted, cleaned and glazed raw fish for 18 months significantly reduced astaxanthin and α-tocopherol levels, while lipid oxidation, measured as thiobarbituric acid reactive substances (TBARS) was limited. In the first experiment, the highest TBARS levels were found during frozen storage in fish fed the lowest level of astaxanthin (40 mg/kg versus 70 mg/kg or 100 mg/kg); unaffected by dietary levels of α-tocopherol (100 mg/kg versus 600 mg/kg), whereas the dietary astaxanthin level (70 mg/kg versus 100 mg/kg) did not influence lipid oxidation in frozen fish in the second experiment. After brine injection, fillets of fish were smoked and a vacuum-packed (95%), sliced product in a transparent laminate was produced. The quality (pigmentation and lipid oxidation) during 3 weeks of illuminated, chill storage (3  °C) was compared for smoked products produced from fresh fish and from fish stored at –28  °C for 12 months and 18 months. Smoked fillets from fish fed 32% fat were found to be less red than those from fish fed 27% fat, and the astaxanthin content and surface redness of the smoked product decreased during chill storage. Lipid oxidation was pronounced in smoked trout, but a high level of α-tocopherol in the fillet significantly reduced lipid oxidation during chill storage of the smoked product. Lipid oxidation in smoked fillets from fish fed 32% fat was more pronounced than in fish fed 27% fat, but increasing the dietary α-tocopherol level from 300 mg/kg feed to 600 mg/kg feed effectively counteracted the negative effect of the high-fat diet on lipid oxidation in the smoked product. Astaxanthin did not affect lipid oxidation in the chill-stored smoked product, in contrast to the frozen, raw fish. Astaxanthin seems to protect against the very early stages of lipid oxidation, while α-tocopherol is more important as an antioxidant at more advanced stages of lipid oxidation. Received: 8 January 1998 / Revised version: 23 March 1998     

Chemical and biochemical changes of hybrid catfish fillet stored at 4 °C and its gel properties

Chemical and biochemical changes of aquacultured hybrid catfish fillet (Clarias macrocephalus × Clarias gariepinus) and its gel-forming ability as affected by age and sex of fish along with storage time were investigated. Fillets were stored at 4 °C for 0, 3, 6, 9, 12 and 15 days. There was no significant effect of sex and age of fish as well as storage time on fat, moisture and ash contents (P > 0.05). The total protein, water soluble protein, and salt soluble protein contents of the fillets significantly decreased with storage time (P < 0.05). On the other hand, pH, total volatile base nitrogen (TVB-N) and autolytic degradation products (ADP) increased as storage time continued (P < 0.05). Decreases in Ca²⁺-ATPase activity and gel properties were observed as storage time increased. However, there was no significant effect of either sex or age of fish on textural properties of gel (P > 0.05). Hybrid catfish fillet stored at 4 °C should be processed within 6 days.     

Reduction of Listeria monocytogenes in Raw Catfish Fillets by Essential Oils and Phenolic Constituent Carvacrol

The antimicrobial activity of various essential oils and carvacrol was determined on fresh raw catfish fillets against a 4-strain Listeria monocytogenes mixture representing serotypes 1/2b, 3b, 4b, and 4c that were predominantly isolated from catfish processing environments. Thyme oil, oregano oil and carvacrol exhibited concentration and time dependent responses in broth against L. monocytogenes; for example 0.5% concentrations resulted in 4 log CFU/mL reduction within 30 min whereas 0.1% concentrations required more than 24 h for the same level of reduction. Lemon, orange, and tangerine oils, at 0.5% showed listeriostatic effect in which 4 log CFU/mL of the initial L. monocytogenes load was unchanged at 4 °C in 10 d whereas 1% concentrations were listericidal in a time dependent manner. Apart from carvacrol, efficacy of tested essential oils in reducing L. monocytogenes and total microbial load from catfish fillet was very limited. Dipping treatment of catfish fillets in 2% carvacrol solution for 30 min at 4 °C reduced L. monocytogenes to an undetectable level from their initial load of 5 log CFU/g and reduced total microbial load from catfish fillets by approximately 5 log CFU/g. In sensory analysis trained panelist preferred control samples over 2% carvacrol treated samples implying potential limitation in applicability of carvacrol for fillet treatments.     

Prevalence and contamination patterns of Listeria monocytogenes in catfish processing environment and fresh fillets

Catfish skins, intestines, fresh fillets, processing surfaces at different production stages, chiller water and non-food contact surfaces were sampled for Listeria monocytogenes and other Listeria species. Among 315 samples, prevalence of L. monocytogenes, Listeria innocua and a group of Listeria seeligeri–Listeria welshimeri–Listeria ivanovii was 21.6, 13.0 and 29.5%, respectively. No Listeria grayi was detected in this survey. While no L. monocytogenes strains were isolated from catfish skins and intestines, the strains were found with a frequency of 76.7% in chilled fresh catfish fillets and 43.3% in unchilled fillets. L. monocytogenes and Listeria spp. were also detected in fish contact surfaces such as deheading machine, trimming board, chiller water, conveyor belts at different stages, and fillet weighing table. Among L. monocytogenes, 1/2b (47.0%), 3b (16.0%) and 4c (14%) were the predominant serotypes isolated, whereas 4b, 4e, 1/2c and 1/2a were detected at much lower frequencies. Genotype analyses of L. monocytogenes isolates using serotyping, pulsed-field gel electrophoresis (PFGE) and enterobacterial repetitive intergenic consensus (ERIC)-PCR revealed that chiller water represented an important contamination source of L. monocytogenes in the chilled catfish fillets of two processing facilities, whereas fillet weighing table significantly contributed to the catfish fillet contamination of the third facility. This study suggests that L. monocytogenes contamination in the processed catfish fillets originates from the processing environment, rather than directly from catfish. Results from this study can aid the catfish industry to develop a plant-specific proper cleaning and sanitation procedure for equipment and the processing environment designed to specifically target L. monocytogenes contamination.     

Effects of High Pressure on Texture and Microstructure of Sea Bass (Dicentrarchus labrax L.) Fillets

High pressure is an innovative non‐thermal food‐preservation technology. We studied the effect of high‐pressure treatment up to 500 MPa for 5 min on physical characteristics of sea bass fillets after 0, 7, and 14 d of refrigerated storage. Color results exhibited an increase of lightness and a slight change of hue, which might be imperceptible in cooked fish. High‐pressure treatment induced a decrease of exudation and water‐holding capacity. Pressure treatment above 300 MPa provoked higher fish hardness after storage than in untreated sample, proving the ability of high pressure to improve textural quality of chilled, stored fish fillet. These assessments were corroborated with microstructure observations. We showed that high‐pressure treatment at 500 MPa allowed, after 7 d of storage, a total aerobic count equivalent to that of untreated fresh fish fillet to be obtained. Thus, high pressure might be considered to be a technology able to improve safety and textural quality of fresh fish fillets.     

Microbial and color quality of fillets obtained from steam-pasteurized deheaded and eviscerated whole catfish

The present study reports on the microbiological quality and surface color of skinless catfish fillets obtained from steam-treated catfish. Total aerobic (APC), psychrotrophic (PPC), coliform (CPC) plate counts, and Hunter color analysis of fillets were performed after treatment and during 14 days of storage at 4°C. Results indicated that as steam treatment duration increased (15–120 s), greater reduction of fillet microflora population was achieved. Microbial counts on fillets obtained from steam-treated catfish were lower than controls at all sample times. Steam treatment for 120 s produced fillets with APC, PPC, and CPC that were 1·6, 1·7, and 1·9 log₁₀cfu g⁻¹lower than control fillets after 4 days at 4°C. Hunter color analysis of fillets revealed no color differences (L, a, b, and Whiteness) between steam-treated and control fillets. The reduction of skin microbial loads by steam prior to skinning of catfish resulted in fillets with superior microbiological quality and no Hunter surface color changes.     

CHOLESTEROL AND PROXIMATE COMPOSITION OF CHANNEL CATFISH (ICTALURUS PUNCTATUS) FILLETS – CHANGES FOLLOWING COOKING BY MICROWAVE HEATING, DEEP-FAT FRYING, AND OVEN BAKING

Effects of microwave heating, deep-fat frying, and conventional oven baking on proximate composition and concentration of cholesterol in channel catfish fillets were examined. The paired fillet technique was employed to control the variability among fish. A total of fifteen catfish were randomly assigned to the three cooking methods. All cooking procedures resulted in moisture loss. Fillets that were deep-fat fried showed the lowest moisture content but the highest fat content, respectively, among three cooking methods. The three cooking methods, on a dry weight basis, all significantly affected cholesterol concentration of cooked catfish compared with raw fillets. Deep-fat frying resulted in a significant decrease of cholesterol and showed the lowest concentration of cholesterol among three cooking methods probably due to leaching of cholesterol into frying oil.     

鱼新鲜度对其烤鱼片中晚期糖基化终末产物形成的影响

本文以马面鱼为原料,基于4℃下7 d内挥发性盐基氮的变化判断鱼肉新鲜度,测定生鱼肉及烤鱼片中与晚期糖基化终末产物(Advanced Glycation End-products,AGEs)形成有密切关系的游离氨基酸、核苷酸、乙二醛等的含量变化,探究鱼新鲜度对其烤鱼片中AGEs形成的影响。结果表明:随着鱼肉新鲜度的降低,生鱼肉及烤鱼片中游离氨基酸和核苷酸的含量升高,烤鱼片中总AGEs、羧甲基赖氨酸、荧光性AGEs和戊糖素的含量在总体上均呈上升趋势,至7 d时总AGEs与羧甲基赖氨酸的含量分别达7.24与4.01 μg/g,说明原料鱼肉新鲜度对烤鱼片中AGEs的含量有重要影响;早中期糖基化产物乙二醛的含量在生鱼肉中变化不明显,但在烤鱼片中呈上升趋势,说明烤鱼片的加工过程与糖基化反应存在直接联系。     

Double freezing of cod fillets: Influence on sensory,physical and chemical attributes of battered and breaded fillet portions

Fillet samples were processed on board a research vessel from cod (Gadus morhua) in different states of rigor mortis. In addition, headed and gutted fish in different states of rigor were frozen and, after ten days of frozen storage, the fish were thawed, processed into fillets and refrozen. During subsequent frozen storage at –24°C of breaded and battered portions processed from the different fillet batches several quality attributes were tested using sensory, physical, and chemical methods. The measurements indicated differences in the quality attributes depending on refreezing and rigor states. Especially the sensory texture attributes gumminess and, with some restrictions, firmness were found to be suitable for distinguishing single frozen (SF) from double frozen (DF) samples. This finding was supported by the outcome of the measurement of penetration force where generally a significantly (p < 0.05) higher force was necessary to penetrate the DF compared to SF samples. DF samples were generally lighter (higher L*) than SF samples. The colour difference δE between both sample types was at least very clear and therefore visible. However, no clear differences between SF and DF samples were found when evaluating the flavour attributes and using instrumental texture profile analysis for texture characterisation. Also, all chemical parameters measured did not allow to clearly distinguish between single and double frozen samples. Therefore, it can be stated that, at least when using cod as raw material for processing battered and breaded portions, the different methods for preparing the fillet blocks will, if at all, only affect the textural quality of the final products.     

Effect of freezing on the physicochemical, textural and sensorial characteristics of salmon (Salmo salar) smoked with a liquid smoke flavouring

This study reports the effect of different refrigeration/freezing treatments on the physicochemical, textural and sensorial properties of farmed Atlantic salmon (Salmo salar) treated with a commercial liquid smoke flavouring. Observations were made on three groups of fillets - group RFS: salted, smoked and stored at 4 °C; group BFS: frozen at −25 °C for 24 h, thawed, salted, smoked and stored at 4 °C; and group AFS: salted, smoked and frozen at −25 °C for 24 h and stored at −18 °C - over a period of 45 days. Scores (on a scale of 1-9) were provided for different sensorial attributes by a panel of 10 trained tasters. Sixty percent of the panellists consistently preferred the AFS fillets. The maximum shelf life associated with each treatment was defined as the last sampling day on which a mean score of ≤5 was awarded for the fillet sensorial attributes by ≥50% of the panellists. Freezing the salmon for 24 h before smoking (BFS) did not increase its shelf life (30 days) over that of refrigerated smoked salmon (RFS). In addition, the former treatment had a negative effect on the adhesiveness, cohesiveness, smoke odour intensity and colour intensity of the flesh. However, maintaining the fish frozen at −18 °C (AFS) increased its shelf life (>45 days) and invested the flesh with greater firmness, cohesiveness and colour intensity.     

Compositional and chill storage characteristics of microwave‐blanched sutchi catfish (Pangasianodon hypophthalmus) fillets

The effect of microwave blanching on quality characteristics of vacuum and conventional polyethylene‐packed sutchi catfish fillets was evaluated under chilled condition. Emphasis has been given to retain the sensory characteristics such as colour and textural properties, which is a major problem in sutchi catfish fillets during extended chill storage. In general, microwave blanching imposed minimum changes on fatty acid and mineral composition of fish meat. A marginal increase in fat content was recorded after microwave heating of fish fillets. The microwave‐blanched fillets showed minimum cooking loss of 3.2 mL per 100 g meat. A slower increase in spoilage parameters was obtained with microwave‐blanched samples compared with unblanched samples, demonstrating the higher storage stability of the sample under chilled conditions. Microwave heating of fish fillets coupled with quick‐chilling and packing under vacuum improved the colour and texture stability of sutchi catfish fillets to a considerable extent. Microwave blanching increased the hardness and chewiness values and decreased the stiffness values of fish fillets. The biochemical and sensory evaluation of microwave‐blanched and vacuum‐packed sutchi catfish fillets showed extended storage life of 21 days, compared with 12 days for unblanched vacuum‐packed samples.     

Injection‐Salting and Cold‐Smoking of Farmed Atlantic Cod (Gadus morhua L.) and Atlantic Salmon (Salmo salar L.) at Different Stages of Rigor Mortis: Effect on Physical Properties

ABSTRACT: Processing of fish is generally conducted postrigor, but prerigor processing is associated with some potential advantages. The aim of this study was to study how 5 processing regimes of cold‐smoked cod and salmon conducted at different stages of rigor influenced yield, fillet shrinkage, and gaping. Farmed cod and salmon was filleted, salted by brine injection of 25% NaCl, and smoked for 2 h at different stages of rigor. Filleting and salting prerigor resulted in increased fillet shrinkage and less increase in weight during brine injection, which in turn was correlated to the salt content of the fillet. These effects were more pronounced in cod fillets when compared to salmon. Early processing reduced fillet gaping and fillets were evaluated as having a firmer texture. In a follow‐up trial with cod, shrinkage and weight gain during injection was studied as an effect of processing time postmortem. No changes in weight gain were observed for fillets salted the first 24 h postmortem; however, by delaying the processing 12 h postmortem, the high and rapid shrinking of cod fillets during brine injection was halved.     

Effects of alkaline and acid pretreatment on the physical properties and nanostructures of the gelatin from channel catfish skins

The objective of this study was to illustrate the correlation between the physical properties and nanostructure of gelatins made of channel catfish (Ictalurus punctatus) skins. The gelatin samples were first pretreated with sodium hydroxide, acetic acid, or water, and then extracted with hot water before the measurement. Physical properties including the yield of protein, viscosity and textural properties were determined on gelatins obtained with different pretreatment conditions. The acid pretreatment group showed the highest gel strength and protein yield, and a reasonable viscosity. The water pretreatment group showed the lowest values for all of the physical properties. Four samples including water, 0.1 M acid and 0.25 and 1.0 M alkaline-pretreated groups’ nanostructures were then studied using atomic force microscopy (AFM). The AFM images showed that the acid-pretreated gelatin was composed of sponge-like aggregates, while the others showed separated individual aggregates. Annular pores were only found in the alkaline pretreatment group. There was no significant correlation between the diameters of the spherical aggregates and the physical properties; however, the different AFM patterns may relate to the gelatin's physical properties.     

Use of immunological techniques for detecting species substitution in raw and smoked fish

 Immunological techniques based on double immunodiffusion and immunodotting have been designed to detect the substitution of halibut (Hippoglossus hippoglossus) for sole (Solea solea) fillets. An immunodotting technique has been also developed to differentiate between smoked cod (Gadus morhua) and smoked eel (Anguilla anguilla) fillets. Antisera raised against water-soluble extracts of raw halibut and smoked cod were employed. Antiserum to cod proteins did not show cross-reaction with eel proteins, whereas antiserum to halibut proteins cross-reacted with sole proteins. Species-specific antiserum to halibut proteins was achieved by adsorption on a polymer of sole proteins. These methods are very easy to perform and provide the basis for the development of rapid tests for detecting species substitution in fish products. Received: 18 April 1996/Revised version: 5 July 1996     

Slaughter value and flesh characteristics of European catfish (Silurus glanis) fed natural and formulated feed under different rearing conditions

The experimental material was comprised of European catfish (Silurus glanis) individuals aged 2.5 years that were reared on natural feed in earthen ponds and individuals aged 1.5 years cultivated intensively on formulated feed in recirculating systems. Weight gain and morphometric parameters were measured along with physical and color characteristics and proximate composition of fillets. Despite the different age and diets of the fish, no differences were observed in the linear biometric indices. The total weight of the fish of both groups and their condition coefficients were also similar. In addition, no differences were reported in their body weight or head and gutted (H&G) carcass and fillet yields. Proximate composition analysis demonstrated a lack of differences in the contents of dry matter. Of the dry matter, differences were reported in the fat content, which was higher in the catfish fed formulated feed. The color of the fillets was characterized by high values of lightness, negative values of redness, and positive values of yellowness, and the fish fed formulated feed displayed higher saturation of green. The flesh of both groups of catfish demonstrated similar pH values and water retention capacity, whereas the values of thermal drip appeared to be higher in the fish fed formulated feed.     

Use of sodium nitrite in salt-curing of Atlantic salmon (Salmo salar L.) – Impact on product quality

Quality changes during processing and quality differences in smoked fillets of Atlantic salmon (4–5 kg) salted with nitrite salt compared to table salted fillets were measured. Quality parameters from right-side fillets dry salted with nitrite salt were compared with the respective left-side fillets treated the same way with table salt. Ten raw right-side fillets were analysed and used as raw material reference. Use of nitrite salt in salt-curing of smoked salmon affected colour to a more reddish hue, tended to increase carotenoid stability and displayed positive effects on NaCl diffusivity. Only slight weight changes and change in texture properties were revealed. The use of nitrite salt displayed no adverse effects like increased content of N-nitrosoamines in smoked products. In fact, significant lower contents of N-nitrosoamines were found in nitrite salted smoked fillets compared to smoked fillets salted with table salt. Relatively high amounts of residual nitrite in nitrite-treated fillets seem to be the most prominent adverse effect caused by the use of nitrite salt in salt-curing of smoked Atlantic salmon.     

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.