Effect of gamma irradiation and frozen storage on chemical and sensory characteristics of rainbow trout (Oncorhynchus mykiss) fillet

The present study was conducted to evaluate the combined effect of low‐dose gamma irradiation (1, 3 and 5 kGy) and frozen storage (5 months at ?20 °C) on chemical and sensory characteristics of rainbow trout (Oncorhynchus mykiss) fillet. Our statistical analysis showed that irradiation process and frozen storage time had a significant effect (P < 0.05) on total volatile nitrogen (TVN), peroxide value (PV), thiobarbituric acid (TBA) and pH. The level of all of these factors increased with increasing frozen storage time. At the end of the fifth month of frozen storage, the lowest and the highest level of TVN, PV and TBA were corresponding to the irradiated samples at 3 and 5 kGy, respectively. In terms of the overall acceptability of their texture, odour, colour and taste, irradiated samples at 3 kGy had the best quality and remained acceptable after 5 months frozen storage. The optimum dose of gamma radiation of rainbow trout fillets according to chemical and sensory analysis was obtained at 3 kGy.     

Relating instrumental texture, determined by variable-blade and Allo-Kramer shear attachments, to sensory analysis of rainbow trout, Oncorhynchus mykiss, fillets

Texture is one of the most important quality attributes of fish fillets, and accurate assessment of variation in this attribute, as affected by storage and handling, is critical in providing consistent quality product. Trout fillets received 4 treatments: 3-d refrigeration (R3), 7-d refrigeration (R7), 3-d refrigeration followed by 30-d frozen storage (R3F30), and 7-d refrigeration followed by 30-d frozen storage (R7F30). Instrumental texture of raw and cooked fillets was determined by 3 approaches: 5-blade Allo-Kramer (AK) and variable-blade (VB) attachment with 12 blades arranged in perpendicular (PER) and parallel (PAR) orientations to muscle fibers. Correlation between instrumental texture and sensory hardness, juiciness, elasticity, fatness, and coarseness was determined. Muscle pH remained constant at 6.54 to 6.64. Raw fillets lost 3.66% of their original weight after 30-d frozen storage. After cooking, weight loss further increased to 15.97%. Moisture content decreased from 69.11 to 65.02%, while fat content remained constant at 10.41%. VBPER detected differences in muscle sample strength (P= 0.0019) and demonstrated effect of shear direction reported as maximum force (g force/g sample). AKPER detected differences in energy of shear (g × mm; P= 0.0001). Fillets that received F30 treatments were less extensible. Cooking increased muscle strength and toughness. Force determined by VBPER was correlated with sensory hardness (r= 0.423, P= 0.0394) and cook loss (r= 0.412, P= 0.0450). VB attachment is accurate, valid, and less destructive in fillet texture analysis. PRACTICAL APPLICATION: A new shearing device was validated with sensory analysis. Settings and parameters obtained could be used to define fillet texture quality associated with muscle fiber orientation.     

A practical quality index method (QIM) developed for aquacultured rainbow trout (Oncorhynchus mykiss)

Quality index method (QIM) was developed for whole (W) and gutted (G) rainbow trout during ice storage. Draft schemes were modified and final schemes consisted of 30 and 15 demerit points, and 12 and 14 days of shelf life was found for whole and gutted rainbow trout, respectively. Linear regression was calculated with storage time and correlation of QI scores was found to be 0.98 and 0.99 for W and G samples, respectively. Moreover, the developed QIM for W and G rainbow trout with this study is a nondestructive and rapid method for the sensory evaluation of rainbow trout.     

Activities of antioxidant enzymes in rats fed with hot-smoked rainbow trout (Oncorhynchus mykiss)

The activities of antioxidant enzymes in rats fed with hot‐smoked rainbow trout (Oncorhynchus mykiss) was investigated. Four diets containing fresh and hot‐smoked rainbow trout flesh and vitamin were prepared and commercial pellet food purchased. Four groups of rats were fed with the diets for 28 days. Body weight was checked weekly. No significant (P > 0.05) differences were found in weight between groups. Malondialdehyde (MDA) values of group B and group D were found to be significantly increased (P < 0.05). Differences in glutathione peroxidase (GPX) and glutathione reductase (GR) values were not significant (P > 0.05) between groups. The difference in superoxide dismutase (SOD) and catalase (CAT) values was found to be significant (P < 0.05). The hot smoked process led to significant changes as decreased in the antioxidant enzymes activities. Our results indicate that determination of MDA, GPX, GR, SOD and CAT parameters in blood may help to point out cancer risk in humans.     

Microstructure and instrumentally measured textural changes of rainbow trout (Oncorhynchus mykiss) gravads during production and storage

BACKGROUND: Gravad fish belong to a group of low‐processed products obtained from fresh fish by rubbing fillets with a mixture of sugar and salt and then placing them in cold storage. Little is known about changes in the tissue during the production and storage of gravads. The aim of the present study was to investigate the microstructural and textural changes in rainbow trout (Oncorhynchus mykiss) gravad during processing and vacuum storage at 3 °C and ?30 °C. RESULTS: Microscopic observations of gravad showed greater compactness of structure when compared with raw trout muscle, characterised by the disappearance of the divisions between adjoining myofibrils in gravad. Freezing, on the other hand, caused the myofibrils to again become more clearly distinguishable despite being partly agglomerated into lamellae. The above changes in structure were accompanied by changes in the textural and rheological properties of the product. It was observed that the texture profile (TPA) changed, resulting in an increase in the cohesiveness and chewiness of the gravads when compared to the raw fillets. There was also a lowering of stress decay during the relaxation test and a decrease in the value of the storage modulus (G′) as analysed by oscillatory rheometry. Further changes observed during storage were mainly concerned with an increase in the hardness and chewiness of gravads. CONCLUSION: Gravading significantly changes the rainbow trout fillets by making the microstructure more compact. This process is accompanied by changes in texture and rheological properties, which next are running during the storage of a chilled or frozen product. These changes are significant enough for potential consumers to be made aware of the fact that the texture of the product changes considerably during its shelf life. Copyright © 2009 Society of Chemical Industry     

Amino acid composition,antioxidant and functional properties of protein hydrolysates from the roe of rainbow trout (Oncorhynchus mykiss)

A fish roe protein hydrolysate from rainbow trout (Oncorhynchus mykiss) trout roe protein hydrolysates (TRH) was produced by pepsin and Alcalase. Proximate, amino acid compositions, protein digestibility and molecular mass distribution of the hydrolysates were determined. The degree of hydrolysis was found to be 44.08% and 27.62% (pepsin and Alcalase, respectively). The two hydrolysates contained a high amount of essential amino acids (33.53% Alcalase–29.39% pepsin). The results showed that TRH by different enzymes is a good source of the leucine and lysine amino acids. The pepsin produced a white powder with higher brightness (L* = 89.50). Alcalase hydrolysate was brownish yellow in colour (L* = 52.85, a* = 10.30, b* = 26.25). The hydrolysates represented excellent antioxidant activities in various concentrations. TRHs showed a good foaming and emulsification properties. The results thus revealed that protein hydrolysates from rainbow trout roe could be used as food additives possessing essential amino acids and antioxidant activity.     

Tissue distribution and residue depletion of metronidazole in rainbow trout (Oncorhynchus mykiss)

Tissue distribution and residue depletion of metronidazole (MNZ) was studied in rainbow trout (Oncorhynchus mykiss) following oral administration of MNZ in feed at the average dose of 25 mg kg^?1 body weight day^?1 for 7 days at 11 ± 2°C. The MNZ concentration in feed was 0.25% while daily feed intake was 1% of body weight. The concentrations of MNZ and its main metabolite, hydroxymetronidazole (MNZOH), in fish tissues were determined by LC-MS/MS. The drug was well distributed in tissues with maximum concentrations on day 1 post-administration. At this time, the mean MNZ concentrations in muscle, skin, kidney, liver and gill were 14 999, 20 269, 15 070, 10 102 and 16 467 µg kg^?1 respectively. MNZ was converted into MNZOH with the ratio of MNZOH:MNZ up to 7% in all fish tissues throughout the withdrawal period. This shows that MNZ itself is the main residue in rainbow trout. MNZ was detected at the level close to the decision limit (0.20 µg kg^?1) in muscle, skin and muscle with adhering skin up to 42 days, while in kidney, liver and gill it was up to 28 days post-administration. MNZOH was eliminated more rapidly from fish tissues and it was present in muscle alone up to 21 days. The elimination half-lives of MNZ and MNZOH in rainbow trout tissues were 1.83–2.53 and 1.24–2.12 days, respectively. When muscle without skin was analysed, higher MNZ and MNZOH concentrations were detected, and for a longer period of time, than in muscle with adhering skin. Thus muscle alone could be more appropriate for the effective residue control of MNZ in rainbow trout. For the same reason, it is also essential to ensure direct cooling immediately after sampling, since MNZ and its metabolite degrade in fish muscle and skin stored in non-freezing conditions.     

Influence of environmental temperature on composition of lipids in edible flesh of rainbow trout (Oncorhynchus mykiss)

The adaptative changes in the fatty acid composition of the main lipid classes in rainbow trout (Oncorhynchus mykiss) edible flesh in response to environmental variation in water temperature were investigated. The research was carried out on intensively farmed trout sampled at different times of the year. Neutral lipids (NL), phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were separated using flash chromatography. Compared with summer acclimatisation, a decrease in neutral lipids of about 19% was observed in winter, accompanied by increases in phosphatidylethanolamine and phosphatidylcholine of about 41 and 29%, respectively. The metabolic adjustment in cold adaptation caused an increase in the levels of unsaturated fatty acids and monoenes of the oleic acid ω9 family and an increase in the levels of unsaturated fatty acids of the linoleic acid ω3 family. At the same time a reduction in the levels of saturated and monounsaturated fatty acids of the oleic acid ω9 family was observed. This pattern turned out to be particularly evident in phosphatidylcholine. The net result of these changes in composition was a significant increase in the polyunsaturated/saturated and polyunsaturated/monoenic fatty acid ratios in the edible flesh. Copyright © 2003 Society of Chemical Industry     

Possibilities to raise vitamin D content of rainbow trout (Oncorhynchus mykiss) by elevated feed cholecalciferol contents

Farmed rainbow trout (Oncorhynchus mykiss) is a widely consumed fish species. The cholecalciferol content in the muscle of rainbow trout is, however, quite low compared with that in several wild fish species. The present study was designed to determine whether it is possible to increase the cholecalciferol content of rainbow trout (initial weight about 500 g) with the use of cholecalciferol‐dosed feeds. Three different cholecalciferol concentrations (8.9, 17.4 and 53.9 μg 100 g ⁻¹ feed) were tested. After 4 months of feeding, the cholecalciferol determinations from samples of muscle and liver were performed using an HPLC method. Here, we suggest that the cholecalciferol content of rainbow trout muscle cannot be increased by feeding them with elevated doses of the vitamin. © 1999 Society of Chemical Industry     

Effect of rainbow trout (Oncorhynchus mykiss) plasma protein on the gelation of Alaska pollock (Theragra chalcogramma) Surimi

ABSTRACT:  The effect of rainbow trout plasma protein (RPP) on the gelation of Alaska pollock surimi was determined to evaluate the possibility of its commercialization as a new protein additive. For modori gel, the breaking force, deformation, whiteness, and water holding capacity increased as the addition amount of RPP (0 to 0.75 mg/g) increased, and decreased at higher concentration of RPP (0.75 to 1.50 mg/g) ( P < 0.05). Protein solubility of modori gel in the mixture of SDS, urea, and β-mercaptoethanol decreased as the addition amount of RPP increased up to 0.75 mg/g, and increased at higher concentration of RPP (0.75 to 1.50 mg/g) ( P < 0.05). The contents of trichloroacetic acid-soluble peptide decreased as the addition amount of RPP (0 to 1.50 mg/g) increased ( P < 0.05). Based on the result of sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE), most myosin heavy chain of surimi was not degraded when RPP was added. Thus, RPP was supposed to act as a protease inhibitor in the gelation of Alaska pollock surimi. An RPP of 0.75 mg/g was the optimal concentration to prevent the gel weakening of Alaska pollock surimi. Compounds with molecular weights less than 10 kDa in RPP had no significant effect on the gelation of Alaska pollock surimi based on the result of the dialyzed RPP.     

Effect of high pressure treatment on the quality of rainbow trout (Oncorhynchus mykiss) and mahi mahi (Coryphaena hippurus)

ABSTRACT:  High pressure processing (HPP) is becoming a promising seafood preservation method. The objective was to investigate the effect of HPP on quality of rainbow trout and mahi mahi during cold storage. Skinless fillets treated with different pressures (150, 300, 450, and 600 MPa for 15 min) and stored at 4 °C were analyzed at 1, 3, and 6 d storage. Red muscle was analyzed for lipid oxidation products by measuring thiobarbituric reactive substances (TBARS) and whole muscle was analyzed for total aerobic count, texture profile analysis, and color. A pressure of 300 MPa effectively inactivated the initial microbial population in rainbow trout (6-log reduction). However, inactivation of the initial population on mahi mahi was only about 4-log reduction at the same pressure. Microbial growth was significantly retarded after HPP. Color results showed that redness ( a * value) of rainbow trout at 300 MPa and above was significantly ( P < 0.05) lower compared to mahi mahi. TBARS values for rainbow trout increased with increased pressure, whereas the same trend was not seen for mahi mahi where maximum oxidation was found at 300 MPa and then declined. This study demonstrates the usefulness of HPP in seafood processing and the influence of species variation on processing parameters. The optimum HPP conditions for influencing lipid oxidation, microbial load, and color changes were found to be 300 MPa for rainbow trout and 450 MPa for mahi mahi.     

Impact of dietary carotenoid and packaging during frozen storage on the quality of rainbow trout (Oncorhynchus mykiss) fed carotenoids

BACKGROUND: The storage life of frozen salmonids is often limited primarily by oxidation and flesh discolouration due to carotenoid degradation. The objective of this research was to determine the carotenoid changes and therefore the muscle colour modifications during 6 months of frozen storage (?18 °C) of whole rainbow trout fed astaxanthin (100 ppm) or canthaxanthin (80 ppm), kept under two different packagings: plastic film and cardboard box. RESULTS: After 6 months of frozen storage, the carotenoid type effect was seen for dry matter while there was no packaging material effect on carotenoid, total lipids, and TBARS contents of trout fillets. The time under frozen storage had an effect on carotenoid and TBARS fillet concentration. The carotenoid‐type effect was noted for the four colour parameters (lightness difference, chroma difference, hue angle difference, and total colour difference) of rainbow trout fillet, while the packaging material effect was observed only for chroma. Frozen storage time had an effect on the four colour parameters of rainbow trout fillet. CONCLUSION: Carotenoid and packaging material effects were more marked for colour parameters than for biochemical parameters. In this study, as fish were frozen and stored as whole fish, fish skin provided good protection against oxidation. Copyright © 2011 Society of Chemical Industry     

A consumer preference study of raw Norwegian rainbow trout (Oncorhynchus mykiss) as sashimi with focus on young adults in Japan

This study was the first consumer study done in Japan, which investigated consumer preferences of raw Norwegian rainbow trout with the use of an experimental design. A full factorial design with three variables (body part, body weight and freshness) was applied at two levels. The results showed that the variation in body part had the greatest effect on the expected and experienced eating quality of raw rainbow trout among seventy-five young adult consumers. The effect was negative and it is possible that the high fat level observed in the belly region does not always lead to better overall likings. The high fat content could also result in the intense fishy odour distinctive to raw salmonidae at consumption and influence the perception of other quality attributes. The present study provides a new way of offering more practical and applicable suggestions to the fish farming industry.     

Comparative assessment of proximate composition,physicochemical parameters,fatty acid profile and mineral content in farmed and wild rainbow trout (Oncorhynchus mykiss)

This study was conducted to determine differences between farmed and wild rainbow trout in terms of proximate and fatty acid composition, physicochemical parameters and mineral content. Fat content of farmed fish fillets was higher, while moisture content was lower than wild fish. However, wild fish had higher pH value and water‐holding capacity comparing to farmed fish. The muscle lipids of farmed fish contained higher proportions of 20:0, 18:1n‐9 and 20:1n‐9; and lower proportions of 18:2n‐6, 20:2cis, 18:3n‐3, 20:3n‐6, 20:4n‐6, 20:5n‐3 and 22:6n‐3 fatty acids than wild fish. The percentage of total saturated fatty acids (SFAs) was similar in both fish. Total polyunsaturated fatty acids (PUFAs), n‐3 PUFAs and n‐3/n‐6 PUFAs ratio were higher in the wild fish comparing to farmed fish, whereas its total monounsaturated fatty acids (MUFAs) and n‐6 PUFAs contents were lower. Among the seventeen minerals analysed in fish flesh, differences existed between farmed and wild rainbow trout in Ca and Fe contents. Moreover, toxic trace minerals (As, Cd, Pb and Hg) were all present in amounts below their toxic levels. The differences observed between farmed and wild fish may be attributed to the diet constituents and environmental conditions of the fish.     

Determination of astaxanthin stereoisomers and colour attributes in flesh of rainbow trout (Oncorhynchus mykiss) as a tool to distinguish the dietary pigmentation source

The presence of carotenoids in animal tissue reflects their sources along the food chain. Astaxanthin, the main carotenoid used for salmonid pigmentation, is usually included in the feed as a synthetic product. However, other dietary sources of astaxanthin such as shrimp or krill wastes, algae meal or yeasts are also available on the market. Astaxanthin possesses two identical asymmetric atoms at C-3 and C-3' making possible three optical isomers with all-trans configuration of the chain: 3S,3'S, 3R,3'S, and 3R,3'R. The distribution of the isomers in natural astaxanthin differs from that of the synthetic product. This latter is a racemic mixture, with a typical ratio of 1:2:1 (3S,3'S:3R,3'S:3R,3'R), while astaxanthin from natural sources has a variable distribution of the isomers deriving from the different biological organism that synthesized it. The high-performance liquid chromatographic (HPLC) analysis of all-trans isomers of astaxanthin was performed in different pigment sources, such as red yeast Phaffia rhodozyma, alga meal Haematococcus pluvialis, krill meal and oil, and shrimp meal. With the aim to investigate astaxanthin isomer ratios in flesh of fish fed different carotenoid sources, three groups of rainbow trout were fed for 60 days diets containing astaxanthin from synthetic source, H. pluvialis algae meal and P. rhodozyma red yeast. Moreover, the distribution of optical isomers of astaxanthin in trout purchased on the Italian market was investigated. A characteristic distribution of astaxanthin stereoisomers was detected for each pigment sources and such distribution was reproduced in the flesh of trout fed with that source. Colour values measured in different sites of fillet of rainbow trout fed with different pigment sources showed no significant differences. Similarly, different sources of pigment (natural or synthetic) produced colour values of fresh fillet with no relevant or significant differences. The coefficient of distance computed amongst the feed ingredient and the trout fillet astaxanthin stereoisomers was a useful tool to identify the origin of the pigment used on farm.     

Differentiation of the rainbow trout (Oncorhynchus mykiss) from Atlantic salmon (Salmon salar) by the AFLP-derived SCAR

A species-specific SCAR marker for rainbow trout, which was used to detect adulteration and fraudulent labeling in Atlantic salmon products, has been developed based on the AFLP analysis and evaluated in this study. The SCAR marker could be amplified and visualized in 1% agarose gel in all tested rainbow trout samples and absent in all salmon samples. Using DNA admixtures, the detection of 1% (0.5 ng), 10% (5 ng) rainbow trout DNA in Atlantic salmon DNA for fresh and processed samples, respectively was readily achieved. The molecular approach was sensitive and demonstrated to be a rapid and reliable method for identifying frauds in salmon products and could be extended for applications of species identification in food industry.     

Change in proximate, amino acid and fatty acid contents in muscle tissue of rainbow trout (Oncorhynchus mykiss) after cooking

Changes in proximate, amino acid and fatty acid composition of farmed, commercially important rainbow trout (Oncorhynchus mykiss) after conventional and microwave cooking were analysed. Rainbow trouts cooked in microwave ovens had statistically significant higher total protein, total fat, and ash than electrical oven‐cooked samples. The amounts of essential and nonessential amino acids were not different between cooking methods, but the difference between raw and cooked samples was significant. Lysine, leusine, methionine, threonine, valine, arginine and histidine were found most in microwave‐cooked rainbow trouts whereas isoleucine, tyrosine and phenylalanine were found most in electrical oven‐cooked samples. As total saturated fatty acid and total monounsaturated fatty acids amount were not statistically different between the cooking methods, the difference between raw and cooked fillets was found statistically significant (P < 0.05). There was no statistically significant difference between raw and cooked fillets in total n‐3 and n‐6 contents.