Quality Assessment of Farmed Rainbow Trout (Oncorhynchus mykiss) during Chilled Storage

ABSTRACT:  The quality changes of farmed rainbow trout ( Oncorhynchus mykiss ) stored in ice for a period of up to 20 (0, 4, 8, 12, 16, and 20) d were determined by chemical (total volatile basic nitrogen [TVB-N], free fatty acid (FFA), thiobarbituric acid (TBA), peroxide value (PV), heme iron), microbiological (total viable counts, TVC), and sensory methods. The TVB-N level showed fluctuations during storage, indicating that TVB-N could not be a good indicator of rainbow trout quality. The TBA values remained low and were found to fluctuate during storage. The PV values and the release of FFA increased ( P < 0.05), while heme iron content decreased during storage. The total viable counts of rainbow trout increased ( P < 0.05) from the initial value of 4.0 log CFU/g (day 0) to 7.04 log CFU/g (day 20) over the period of storage. This study showed that sensory analysis of rainbow trout correlated well with the microbiological analysis. The results of this study according to microbiological and sensorial data indicated that the shelf life of rainbow trout stored in ice was approximately 9 to 11 d.     

Enhancement of Omega-3 Fatty Acid Content in Rainbow Trout (Oncorhynchus mykiss) Fillets

ABSTRACT:  A commercial diet for rainbow trout ( Oncorhynchus mykiss ) was supplemented with 0 (control), 8.5%, or 15.0% (w/w) of flaxseed oil (FO). Trouts were harvested on days 0, 30, 60, 90, and 120. Boneless skinless trout fillets were recovered from fish and analyzed for fatty acid profile (FAP) and total fat. While the total fat levels of fillets were not ( P > 0.05) affected by FO supplementation, the FAP was. The lowest ( P < 0.05) proportion of saturated fatty acids was obtained from 15%, followed by 8.5% FO group, and the control group. The opposite results were observed for the unsaturated fatty acids. The highest ( P < 0.05) content of omega-3 fatty acids (ω-3 FA) in fillets was determined in the 15.0%, followed by the 8.5% FO group, and the control group. While the 15.0% and 8.5% of FO supplementation increased ( P < 0.05) concentration of linolenic acid (ALA, 18:3n3) in fillets, the eicosapentaenoic (EPA, 20:5n3) and docosahexaenoic acids (DHA, 22:6n3) contents decreased ( P < 0.05). At the same time, higher ( P < 0.05) concentration of linoleic (L, 18:2n6) and lower ( P < 0.05) concentration of arachidonic acids (AN, 20:4n6) in fillets were obtained in the 15.0% FO group compared with the control group. The ω-3/ω-6 FA ratio was also improved ( P < 0.05) by supplementing basal diet with 15.0% FO. Our results suggest that trout fillets with enhanced content of ω-3 FA can be developed from trout raised in aquaculture systems fed diets supplemented with 15.0% FO. These fillets could be a basis to develop novel functional aquatic foods for some niche markets.     

二、三倍体虹鳟肌肉感官品质差异的对比分析

为研究二倍体虹鳟和三倍体虹鳟感官品质差异,分析同一亲本、同一养殖条件下二、三倍体虹鳟肉色、肉质和风味物质的组成及含量的差异。结果表明：在肉色方面,二倍体虹鳟肌肉黄色值显著大于三倍体虹鳟（P＜0.05）,亮度值和红色值无显著差异;在肉质方面,三倍体虹鳟肌肉弹性和咀嚼性显著高于二倍体虹鳟（P＜0.05）,持水力和pH值等无显著差异;在滋味物质方面,三倍体虹鳟肌肉滋味组成相对二倍体虹鳟较为丰富,有鲜、咸、苦和甜等味道;在挥发性物质组成方面,二、三倍体虹鳟肌肉挥发性物质均由77 种化合物组成,气味活度值较大的特征性气味物质主要有1-辛烯-3-醇、己醛、辛醛、壬醛和(E)-2-壬烯醛,整体呈现青草味、脂肪味及水果香味,三倍体虹鳟肌肉中总特征性气味物质的气味活度值显著高于二倍体虹鳟（P＜0.05）。本研究表明二、三倍体虹鳟具有不同的感官品质特征。     

Comparison of Variable-Blade to Allo-Kramer Shear Method in Assessing Rainbow Trout (Oncorhynchus mykiss) Fillet Firmness

Abstract: A variable‐blade (VB) attachment was compared to the Allo‐Kramer (AK) shear attachment for texture analysis of rainbow trout fillets from 2 experiments; effects of attachment configuration, storage regimen, and cooking temperature are evaluated. In the 1st experiment, AK detected differences in force measurement, and VB showed that the perpendicular orientation yielded the highest response (P < 0.05). Fillets refrigerated (4 °C) for 0 d were firmer than fillets stored for 14 d (337.36 compared with 275.90 g/g). Raw fillets were firmer than cooked fillet (333.79 compared with 279.46 g/g). In the 2nd experiment, frozen storage at –25 °C for 30 d after refrigerated storage (R3F30 and R7F30) decreased VB shear force (P= 0.0019) and AK energy of shear (P= 0.0001) by 1.5‐ and 2‐fold compared to those evaluated after refrigerated storage for 3 and 7 d (R3 and R7), respectively. Cooking increased VB and AK texture for all storage regimens (P < 0.05). In both studies, instrumental texture did not correlate with alkaline‐insoluble hydroxyproline (P > 0.05). Shear direction affected force generated by the VB attachment, and this attachment could discriminate shear force differences due to cooking and frozen‐storage. Practical Application: Fillet texture was determined by a recently developed device and compared to texture determined by the Allo‐Kramer shear attachment; both responses were related to collagen content. The VB attachment defined fillet texture as affected by cooking and storage condition.     

外源性谷氨酰胺对虹鳟稚鱼生长和肠道形态的影响

旨在观察L-谷氨酰胺对虹鳟(Oncorhynchus mykiss)稚鱼生长和十二指肠形态的影响.试验共分6个处理,在以白鱼粉为主的饵料中分别添加0%、0.25%、0.5%、0.75%、1.0%和2.0%Gln,分别于4周末和12周末测定生长和肠道形态指标.与对照组相比,添加0.50%Gln组12周的生长表现较好,体重和体长分别提高7.28%和7.25%,饵料系数显著降低(P＜0.05).添加0.25%～1.0%Gln各处理的成活率均较对照组显著(P＜0.05)或极显著(P＜0.01)提高.与对照组相比,添加外源性Gln 4周时对肠道形态未产生有益作用,12周末添加0.25%P0.75%Gln对十二指肠绒毛高度、绒毛直径和黏膜厚度未产生显著影响,但添加1.0%和2.0%组显著降低了绒毛直径、绒毛高度和黏膜厚度(P＜0.05),也显著降低肠腺深度(P＜0.05).     

Rapid Near Infrared Spectroscopic Method for the Detection of Spoilage in Rainbow Trout (Oncorhynchus mykiss) Fillet

The possibility of using visible and short‐wavelength near‐infrared (SW‐NIR: 600 to 1100 nm) spectroscopy to detect the onset of spoilage and to quantify microbial loads in rainbow trout (Oncorhynchus mykiss) was investigated. Spectra were acquired on the skin and flesh side of intact trout fillet portions and on minced trout muscle samples stored at 4 °C for up to 8 d or at room temperature (21 °C) for 24 h. Principal component analysis (PCA) and partial least squares (PLS) chemometric models were developed to predict the onset and degree of spoilage. PCA results showed clear segregation between the control (day 1) and the samples held 4 d or longer at 4 °C. Clear segregation was observed for samples stored 10 h or longer at 21 °C compared with the control (0 h), indicating that onset of spoilage could be detected with this method. Quantitative PLS prediction models for microbial loads were established. For trout fillets, 4 °C: R= 0.97, standard error of prediction (SEP) = 0.38 log colony‐forming units (CFU)/g (flesh side); R= 0.94, SEP = 0.53 log CFU/g (skin side); R= 0.82, SEP = 0.82 log CFU/g for minced fish held at 21 °C. These results indicate that SW‐NIR in combination with multivariate statistical methods can be used to detect and monitor the spoilage process in rainbow trout and quantify microbial loads rapidly and accurately.     

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.     

Rainbow trout (Oncorhynchus mykiss) can eliminate chiral organochlorine compounds enantioselectively

Dietary accumulation of four chiral organochlorine compounds--alpha-hexachlorocyclohexane (alpha-HCH), trans-chlordane, and chlorobiphenyls (CBs) 95 and 136-by immature rainbow trout (Oncorhynchus mykiss) was studied to determine if fish can accumulate and eliminate these compounds enantioselectively. Fish rapidly accumulated all four compounds from food spiked at micrograms per gram concentrations during a 40-d feeding period. Depuration half-lives were from 13 d for (+/-)-alpha-HCH to 375 d for (+/-)-CB 136. Fish preferentially eliminated (-)-trans-chlordane and (+)-CB 136, with significant nonracemic residues observed after 20 d. These results are consistent with field measurements of these compounds in fish as well as known metabolic pathways. Enantiomeric fractions (EFs) for these two compounds changed significantly over the course of the experiment, suggesting that trout were enantioselectively biotransforming the compounds during the 238-d depuration phase. CB 95 and alpha-HCH residues were racemic throughout the experiment. High biomagnification factors for CB 95 suggest that it was not metabolized. Minimum values for metabolic elimination rates calculated from EF suggest that at least 58% of the trans-chlordane depuration rate can be attributed to metabolism, and all of the CB 136 depuration rate can be attributed to it. This study highlights the potential of chiral analysis as a tracer of in vivo biotransformation processes of xenobiotic compounds.     

Effect of Different Cooking Methods on Minerals,Vitamins, and Nutritional Quality Indices of Rainbow Trout (Oncorhynchus mykiss)

In this study, the influence of four cooking methods (baking, boiling, microwaving, and frying) on the nutritional value of rainbow trout was determined. Proximate, fatty acid composition, vitamin, mineral contents, and nutritional quality indices of rainbow trout were investigated (i.e., before and after cooking treatments). In all samples, there was reduction of total n-3 than raw fish fillets. Considering overall nutritional quality indices, vitamin, and mineral contents; baking and boiling were the best cooking methods among other methods used in this study.     

Quality and Shelf Life of Cold and Frozen Rainbow Trout (Oncorhynchus mykiss) Fillets: Effects of Fish Protein-Based Biodegradable Coatings

The Klunzinger’s ponyfish (Equulites klunzingeri) protein powder extracted with acid or alkali aided process as a biodegradable coating material for rainbow trout (Oncorhynchus mykiss) fillets during cold (+2°C) and frozen storage (–18°C) were investigated. The coating with alkaline treated protein (AlPC) and acid treated protein (AcPC) extended the shelf life of fillets from 11 to 14 days in cold storage and improved the quality parameters in three months frozen storage period. According to total viable count and total psychrophile count results, bacteria grew more quickly in uncoated fillets than coated fillets. The protein-based coating did prevent spoilage of the rainbow trout fillets as reflected by a decrease in pH, total volatile base-nitrogen and free fatty acids during cold and frozen storage period. Therefore, this study demonstrated that fish protein-based coating had a positive effect on maintaining the rainbow trout fillets quality, and edible coatings from discard fish can offer a promising alternative for preserving fish fillets.     

Increased shelf life of Oncorhynchus mykiss (Rainbow trout) through Cu-Clay nanocomposites

Food Science and Biotechnology - Microbial growth is widely responsible for shortened shelf life of cold water-living fish products. So, it seems that current chemical-based food packaging has no...     

Texture Properties of Farmed Rainbow Trout (Oncorhynchus mykiss): Effects of Diet,Muscle Fat Content and Time of Storage on Ice

Groups of rainbow trout (Oncorhynchus mykiss) fed diets with low or high fat content were stored on ice for up to 11 days in two separate experiments. After 4, 9 and 11 days storage on ice in the first experiment and after 5, 8 and 11 days in the second experiment the fish were filleted by hand and fillet gaping was evaluated. Texture properties were studied using an Instron compression test. pH was measured in all fillets. In fillets from the second experiment, also fat content and autolytic protease activity were measured. Diet affected fillet fat content and texture properties. Fish fed high fat diet exerted less resistance against compression, indicating a softer consistency. Force at yield point and slope were not significantly affected by diet. The high fat group had higher autolytic protease activity than the low fat group. The results from the Instron measurements indicated that the fish became softer and less tough during 11 days storage on ice. A slight, but statistically significant increase in pH with time was observed in both experiments. In the first experiment a reduction in gaping scores was observed during storage, as opposed to a significant increase in the second experiment. The texture parameters yield point and slope were negatively correlated to gaping in the second experiment.     

茶多酚-壳聚糖复合液对虹鳟鱼肉贮藏品质和菌群结构的影响

针对虹鳟鱼在贮藏过程中易受到微生物的污染而发生腐败变质的问题,将3 g/L茶多酚和10 g/L壳聚糖混合制成复配保鲜剂,浸泡涂膜覆盖于虹鳟鱼表面。以感官评价、挥发性盐基氮含量、菌落总数及菌群结构等为指标,研究保鲜剂对4℃贮藏虹鳟鱼肉贮藏品质变化的影响。结果表明:茶多酚和壳聚糖单独使用或复合使用均能延缓腐败的发生;复配保鲜剂能将4℃贮藏虹鳟鱼的货架期从8 d延长至13 d,效果优于单独使用;未经处理的新鲜虹鳟鱼片菌群由16个菌属组成,腐败末期则以假单胞菌属为优势菌属,而复合保鲜剂涂膜会明显抑制假单胞菌属的生长,进而减缓鱼肉品质劣变。综上,茶多酚和壳聚糖的复配保鲜剂有助于通过抑制优势腐败菌的生长延缓4℃贮藏条件下虹鳟鱼的腐败变质。     

Modified Atmosphere Packaging and UV-C Radiation on Shelf Life of Rainbow Trout (Oncorhynchus Mykiss)

Effects of modified atmosphere packaging (MAP) in combination to UV-C radiation on rainbow trout fillets were examined. The samples were submitted to two treatments: (T1) aerobic package; (T2) MAP+UV-C radiation (80% CO₂/20% N_2; 106.32mJ/cm²) and were analyzed daily for microbiological (mesophilic and psychrotrophic count) and chemical (biogenic amines) parameters. MAP+UV-C radiation (T2) promoted lag phase formation and lower number of colonies in the stationary phase as well as retarded cadaverine production during storage time. MAP+UV-C radiation retard microbial growth and delay chemical changes enhancing the shelf life of rainbow trout fillets by at least twice.     

大西洋三文鱼和虹鳟鱼双重PCR检测方法的建立及应用

为了实现大西洋三文鱼和虹鳟鱼的物种掺假快速检测,本研究建立了一种基于双重PCR（普通和荧光）的物种鉴定方法。通过序列分析,分别基于线粒体COⅠ和Cyt b基因设计大西洋三文鱼和虹鳟鱼特异性引物,验证引物的特异性并对双重PCR反应体系进行优化,建立大西洋三文鱼和虹鳟鱼的双重PCR快速鉴定方法。利用本研究设计的引物,仅大西洋三文鱼和虹鳟鱼可以分别扩增出108 bp和207 bp的特异性条带,而其他23种非目标物种均未有扩增条带。经验证,在双重PCR反应体系中,大西洋三文鱼和虹鳟鱼引物的最佳添加量分别为0.1和0.4 μmol/L,熔解温度分别约为81.5 ℃和85 ℃。利用该方法从29份市售“三文鱼”样品中检测到6份大西洋三文鱼和3份虹鳟鱼,且与DNA条形码比对结果一致。本研究建立的大西洋三文鱼和虹鳟鱼双重PCR（普通和荧光）鉴定方法具有良好的特异性和适用性,为大西洋三文鱼和虹鳟鱼物种鉴定提供了可靠的技术手段。     

Color Evaluation in Raw, Baked and Smoked Flesh of Rainbow Trout (Onchorhynchus mykiss) Fed Astaxanthin or Canthaxanthin

Color of rainbow trout (Onchorynchus mykiss) was investigated using sensory and instrumental analysis. When judged in pairs with equal carotenoid concentration, astaxanthin caused less whiteness, higher chromaticity and more red hue of trout flesh than canthaxanthin. Sensory assessed whiteness, chromaticity and red hue significantly correlated with instrumental values for lightness, chromaticity and hue [CIE (1976) L*a*b* and H(°)_ab]. Multivariate regression analysis improved the predictability for all sensory variables compared with univariate analysis. Prediction of carotenoid concentration from instrumental values was better for astaxanthin than for canthaxanthin.     

Effect of Vacuum and Modified Atmosphere on Enterobacteriaceae Count Determined in Rainbow Trout (Oncorhynchus Mykiss) and Carp (Cyprinus Carpio) Steaks

The aim of our research was to determine the presence and examine the change in total number of Enterobacteriaceae in trout and carp cuts packed in vacuum and modified atmosphere. To conduct the study, three sample groups of cleaned trout and carp cuts were formed. The first two groups were packaged in modified atmospheres with different gas ratios: 60%CO₂+40%N₂ (I group) and 40%CO₂+60%N₂ (II group), whereas the third group of fish cuts were vacuum packaged. Our results suggest that modified atmosphere packaging of fresh fish with an appropriate percentage of CO₂ might reduce the risk of poisoning people with Enterobacteriaceae.     

Lipid Hydrolysis and Oxidation Related to Astaxanthin Content in Light and Dark Muscle of Frozen Stored Rainbow Trout (Oncorbynchus mykiss)

Astaxanthin decreased significantly during frozen storage in both light and dark muscle of farmed rainbow trout (Oncorhynchus mykiss). Astaxanthin sunolementation did not affect lipid hydrolysis and oxidation during frozen storage of fish muscle. Deposition of astaxanthin was higher in dark muscle than in light muscle. Astaxanthin decreased in both supplemented and nonsupplemented fish. The sum of trans-astaxanthin and its cis-isomers decreased during frozen storage, indicating mechanisms other than trans-cis isomerization were causes. α-Tocopherol decreased to the same extent in both light and dark muscle for both diets.     

Heat-induced Gelation of Minced Rainbow Trout (Salmo gairdneri:) Effect of pH, Sodium Chloride and Setting

The structure formation of minced rainbow trout was monitored during heating from 30°C to 85°C by a dynamic rheological method. The maxima of storage modulus (G') were found at 37°C and in the range of 45°C to 60°C. The largest differences in rigidity resulted from seasonal variations. Firmest protein matrix was obtained by using well-fed fish as raw material, by setting the gels at 35°C and using a pH value around 6.1. Sodium chloride in the range 1–2% had little effect on the final rigidity of the minced rainbow trout gels.