Salmon Fat Content Estimation by Near Infrared Transmission Spectroscopy

Near infrared transmission (NIT) specroscopy spectrum in the region 850–1050 nm was used for prediction of the fat content in fresh salmon fillets. The square error of prediction was 0.49%, and the correlation between measured and predicted fat from the NIT-spectrum was 0.99. The only sample preparation needed was simple homogenization of the fillet prior to analysis.     

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.     

Fat Content and Fillet Shape of Atlantic Salmon: Relevance for Processing Yield and Quality of Raw and Smoked Products

ABSTRACT: Relevance of fat content and fillet shape of Atlantic salmon for quality and yield during smoking processing was investigated. Fat content significantly influenced quality of raw and smoked products, although the interactions varied according to the raw material used and smoking temperature. In raw and smoked fillets, increasing fat content coincided with increasing L* and b*-values and decreasing fat holding capacity. In smoked salmon, fat content also correlated positively to the a*-value, smoke-intensity-/wood-fire flavor and fatty texture, and negatively to water holding capacity and shear-force. Weight loss during salting and smoking decreased with increasing fat content, and voluminous shaped fillets gave higher yield than slim fillets. Keywords: Atlantic salmon, fat content, fillet shape, salmon quality, processing     

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.     

VIS/NIR spectroscopy for non-destructive freshness assessment of Atlantic salmon (Salmo salar L.) fillets

Visible/near-infrared spectroscopy has been evaluated for use in freshness prediction and frozen-thawed classification of farmed Atlantic salmon fillets, where fresh samples were stored as whole fish in ice. A handheld interactance probe for performing rapid measurements of single fillets and an imaging spectrometer for online analysis at an industrial speed of one fillet per second, have been used. Freshness as storage days in ice is predicted with an accuracy of 2.4 days for individual fillets, whereas frozen-thawed salmon fillets are completely separated from fresh fillets. The prediction results are comparable to previous results using the Quality Index Method with trained panelists. The region between 605 and 735 nm, which excludes interference by carotenoids and water, is appropriate for both frozen-thawed classification and freshness prediction of salmon fillets. The results indicate that the spectral changes are explained mainly by oxidation of heme proteins during the freeze–thaw cycle and during chilled storage in ice.     

不同方法提取的花生油对煎炸三文鱼风味成分的影响

本实验目的是研究花生油对煎炸三文鱼风味的影响,采用顶空固相微萃取-气相色谱质谱联用(HS-SPME-GC-MS)技术,比较用水媒法和压榨法得到的6种花生油煎炸三文鱼后对其挥发性风味组分的影响。结果表明:经6种花生油煎炸后,三文鱼中的挥发性风味物质均明显增多,共检测出87种挥发性物质,主要为醛类、醇类和烃类(烷烃、烯烃、芳香烃),以及含氮杂环吡嗪类等。其中醛类数量增加最为明显,其次是醇类物质。而烃类物质种类数量变化不大,但6种样品中烃类物质的相对含量平均下降了60.41%。6种花生油煎炸后的挥发性成分中均检测到吡嗪类化合物。利用富含吡嗪类化合物的花生油煎炸三文鱼时,由于其本身带有的吡嗪类化合物易挥发,大部分在高温煎炸过程中损失,并不能赋予煎炸三文鱼特殊的烤花生风味。两种提取方法得到的6种花生油,煎炸三文鱼时得到的主体挥发性物质种类及其相对含量相似,差别较小。     

A Novel Tensile Test Method to Assess Texture and Gaping in Salmon Fillets

ABSTRACT: A new tensile strength method was developed to quantify the force required to tear a standardized block of Atlantic salmon muscle with the aim of identifying those samples more prone to factory downgrading as a result of softness and fillet gaping. The new method effectively overcomes problems of sample attachment encountered with previous tensile strength tests. The repeatability and sensitivity and predictability of the new technique were evaluated against other common instrumental texture measurement methods. The relationship between sensory assessments of firmness and parameters from the instrumental texture methods was also determined. Data from the new method were shown to have the strongest correlations with gaping severity (r =−0.514, P < 0.001) and the highest level of repeatability of data when analyzing cold-smoked samples. The Warner Bratzler shear method gave the most repeatable data from fresh samples and had the highest correlations between fresh and smoked product from the same fish (r = 0.811, P < 0.001). A hierarchical cluster analysis placed the tensile test in the top cluster, alongside the Warner Bratzler method, demonstrating that it also yields adequate data with respect to these tests. None of the tested sensory analysis attributes showed significant relationships to mechanical tests except fillet firmness, with correlations (r) of 0.42 for cylinder probe maximum force (P = 0.005) and 0.31 for tensile work (P = 0.04). It was concluded that the tensile test method developed provides an important addition to the available tools for mechanical analysis of salmon quality, particularly with respect to the prediction of gaping during factory processing, which is a serious commercial problem. Practical Application: A novel, reliable method of measuring flesh tensile strength in salmon, provides data of relevance to gaping.     

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.     

Use of image analysis to determine fat and connective tissue in salmon muscle

 An attempt was made to measure connective tissue and fat in salmon fillets using image analysis. Farmed salmon fillets were digitized by video camera and transferred to an image analysis program. A Laplace transformation was performed, and the image was segmented into different scales of grey. Particle analysis was applied to the binary pictures to calculate the percentage of white stripes in the total surface of the fillet, which were related to the percentage of connective tissue (CT) and fat. Although low correlation coefficients were obtained, it could be assumed that the video image analysis method is sensitive enough to detect great variations in fat content, which could prove useful in industrial applications. In contrast, CT was found to have less influence on the visual appraisal of the fillet surface. Received: 17 July 1998 / Revised version: 20 October 1998     

Effects of High-Pressure Processing on the Quality of Sea Bass (Dicentrarchus labrax) Fillets During Refrigerated Storage

The aim of this study was to evaluate the effect of high-pressure processing (HPP) on the quality of fresh sea bass fillets using two pressure levels (250 and 400 MPa; 5 min pressure holding time). Vacuum-packed fillets were used as control samples, and all fillets were stored under refrigerated conditions for 18 days. The microbiological, chemical, physical, and sensory parameters were followed. Both HPP treatments increased the microbiological shelf life of sea bass fillets. In day 14, control samples reached the upper acceptability limit (7 log colony-forming units (CFU)?g^?1), while fillets treated at 250 and 400 MPa had 3.2 and 1.4 log CFU g^?1, respectively. In general, hydrogen sulphide-producing bacteria and Enterobacteriaceae loads were below the detection limit in HPP treatments. Results from nucleotide analysis indicate that HPP treatments reduced the conversion of inosine 5′-monophosphate to inosine. HPP also influenced fillet sensory characteristics. The most evident changes in fillets were the increase in whiteness, the loss of translucency, and a firmer consistency. The effect was more pronounced in the treatment at 400 MPa. Lipid oxidation increased in HPP-treated samples, being more accentuated in the treatment at 400 MPa. Instrumental smell intensity increased in both HPP treatments, though the sensory panel did not detect any rancid or other unpleasant odours. No effect was observed in the amount of volatile bases or in pH values. In conclusion, HPP treatments showed potential application for new fish product development with increased microbiological safety and shelf life, longer freshness, and unique characteristics (e.g. firmer and whitish).     

Sensory and Physical Changes in Chilled Farmed Coho Salmon (Oncorhynchus kisutch): Effect of Previous Optimized Hydrostatic High-Pressure Conditions

The effect of a previous hydrostatic high-pressure (HHP) treatment on sensory and physical quality of chilled coho salmon (Oncorhynchus kisutch) was investigated. As a first stage, a 2² factorial design based on the response surface methodology was used for optimization of HHP conditions; for it, the effects on color uniformity, white spots appearance, elasticity, and hardness were analyzed. In a second stage, optimized HHP conditions (135 MPa for 30 s, 170 MPa for 30 s, and 200 MPa for 30 s; treatments T-1, T-2, and T-3, respectively) were applied as previous treatment to chilling, being sampling carried out on salmon muscle at days 0, 6, 10, 15, and 20. A marked effect on sensory and physical parameters was detected after HHP treatment and throughout the chilled storage. According to odor (rancid, putrid), texture (elasticity, gaping, firmness), and color (L* value) attributes, fish corresponding to T-1 condition was shown to have better-maintained quality throughout the chilled storage than fish belonging to T-2 and T-3 conditions; additionally, a quality enhancement (putrid odor, cohesivity, gaping) was found when compared with control samples. In agreement to the preliminary optimization study, it is concluded that T-1 condition can provide the most effective HHP pre-treatment to better maintain sensory and physical properties when salmon muscle is to be commercialized as a fresh product. Results obtained for the quality evolution of chilled fish attest the importance of establishing a judicious selection of previous HHP treatment parameters to minimize undesirable changes related to sensory and physical characteristics.     

Salmon Fillet Texture is Determined by Myofiber-Myofiber and Myofiber-Myocommata Attachment

ABSTRACT: Atlantic salmon ( Salmo salar ) fillets were stored on ice for a maximum of 14 d to determine which muscle structures are associated with changes in texture and rigor. Texture was measured as shear force and the changes correlated with structural alterations. Texture decreased significantly within 24 h in parallel with loss of attachment of muscle fibers. Loss of rigor stiffness by 5 d was associated with myofiber detachment from the myocommata. These results show that fillet texture depends on several distinct structures and events, initially including breaks in the cell cytoskeleton and loss of fiber-fiber attachment and later breaks in the connective tissue and fiber detachment from the myocommata.     

Visible/near-infrared spectroscopy detects autolytic changes during storage of Atlantic salmon (Salmo salar L.)

Visible (VIS)/near-infrared (NIR) spectroscopy was used to investigate spectroscopic changes occurring during storage of Atlantic salmon fillets with and without bacterial growth. A storage experiment was conducted for 11 d postmortem. Bacterial growth was inhibited by soaking a group of salmon fillets in 3 mM NaN3 prior to storage, while a control group retained its normal bacterial growth. Spectra were obtained by directly applying the spectroscopic probe onto the loin part of each fillet stored under conditions accelerating degradation. Principal component analysis (PCA) was used to monitor and compare spectroscopic development of the 2 groups and the results showed that VIS/NIR spectral changes occurred in the control as well as the treated group of samples within a single day after filleting. After 2 d of storage, stored samples were distinguishable from those fresh in both groups and it was only after the microbial spoilage became pronounced (8 to 9 log colony forming unit [CFU]/g) that the spectra of the spoiled control samples could be differentiated from spectra of the treated samples with no bacterial growth. Microbial growth is therefore not the only explanation for the spectral variations prior to microbial spoilage. Nonmicrobial, autolytic changes including possible changes in the physical properties are also contributing. Our results show that VIS/NIR spectroscopy can detect autolytic changes occurring in salmon muscle during the early stage of storage, independent of microbial growth. PRACTICAL APPLICATION: Important spectroscopic changes occur even when microbial growth is not apparent. This indicates that VIS/NIR spectroscopy may be used to determine the degree of freshness before microbial spoilage becomes relevant.     

Chitosan and Protein Coatings Affect Yield, Moisture Loss, and Lipid Oxidation of Pink Salmon (Oncorhynchus gorbuscha) Fillets During Frozen Storage

The effects of chitosan (CH1 = 1% and CH2 = 2% solution), egg albumin (EA), soy protein concentrate (SPC), pink salmon protein powder (PSP), and arrowtooth flounder protein powder (AFP) as edible coatings on quality of skinless pink salmon fillets were evaluated during 3 mo frozen storage. Coating with 2% chitosan (CH2) resulted in significantly higher yield than coating with PSP and AFP. The thaw yield of salmon fillets coated with CH2 was higher than those of the control and fillets coated with AFP. The noncoated, CH1‐, and CH2‐coated fillets had similar drip loss (0.4% to 1.2%), which was lower than those observed for PSP‐ and AFP‐coated fillets. All fillet samples had similar cook yield (84.2% to 88.8%). The fillet coated with CH1, CH2, SPC, and EA had significantly higher (P < 0.05) moisture content after thawing than the control noncoated fillets. Coating with CH1 and CH2 was effective in reducing about 50% relative moisture loss compared with the control noncoated fillets. Chitosan (CH1 and CH2) and SPC delayed lipid oxidation. There were no significant (P > 0.05) effects of coating on a*, b*, and whiteness values for cooked fillets after 3 mo frozen storage.     

Product Yield and Gaping in Cold-smoked Atlantic Salmon (Salmo salar) Fillets as Influenced by Different Injection-salting Techniques

Product yield and fillet gaping severity were determined in cold‐smoked Atlantic salmon fillets subjected to injection‐salting. Effects of process parameter settings (brine injection pressure, number of repeated injections, needle speed, injection of brine in 1 or 2 directions, and chilled fillet resting before smoking) were tested. Repeated injections increased the yield up to 5.3% (wt/wt). Increasing injection pressure significantly increased the severity of fillet gaping in smoked fillets by 18%. Brine injection directions or needle speed did not affect smoking yield. The stability of the injection system was high. The results show that choice of process parameter settings during injection‐salting affects product yield after smoking.     

Mapping of Fat and Moisture Distribution in Atlantic Salmon Using Near-Infrared Hyperspectral Imaging

A nondestructive and rapid method using near-infrared (NIR) hyperspectral imaging was investigated to determine the spatial distribution of fat and moisture in Atlantic salmon fillets. Altogether, 100 samples were studied, cutting out from different parts of five whole fillets. For each sample, the hyperspectral image was collected with a pushbroom NIR (899–1,694 nm) hyperspectral imaging system followed by chemical analysis to measure its reference fat and moisture contents. Mean spectrum were extracted from the region of interest inside each hyperspectral image. The quantitative relationships between spectral data and the reference chemical values were successfully developed based on partial least squares (PLS) regression with correlation coefficient of prediction of 0.93 and 0.94, and root mean square error of prediction of 1.24 and 1.06 for fat and moisture, respectively. Then the PLS models were applied pixel-wise to the hyperspectral images of the prediction samples to produce chemical images for visualizing fat and moisture distribution. The results were promising and demonstrated the potential of this technique to predict constituent distribution in salmon fillets.     

Computer vision-based evaluation of pre- and postrigor changes in size and shape of Atlantic cod (Gadus morhua) and Atlantic salmon (Salmo salar) fillets during rigor mortis and ice storage: effects of perimortem handling stress

The present study describes the possibilities for using computer vision-based methods for the detection and monitoring of transient 2D and 3D changes in the geometry of a given product. The rigor contractions of unstressed and stressed fillets of Atlantic salmon (Salmo salar) and Atlantic cod (Gadus morhua) were used as a model system. Gradual changes in fillet shape and size (area, length, width, and roundness) were recorded for 7 and 3 d, respectively. Also, changes in fillet area and height (cross-section profiles) were tracked using a laser beam and a 3D digital camera. Another goal was to compare rigor developments of the 2 species of farmed fish, and whether perimortem stress affected the appearance of the fillets. Some significant changes in fillet size and shape were found (length, width, area, roundness, height) between unstressed and stressed fish during the course of rigor mortis as well as after ice storage (postrigor). However, the observed irreversible stress-related changes were small and would hardly mean anything for postrigor fish processors or consumers. The cod were less stressed (as defined by muscle biochemistry) than the salmon after the 2 species had been subjected to similar stress bouts. Consequently, the difference between the rigor courses of unstressed and stressed fish was more extreme in the case of salmon. However, the maximal whole fish rigor strength was judged to be about the same for both species. Moreover, the reductions in fillet area and length, as well as the increases in width, were basically of similar magnitude for both species. In fact, the increases in fillet roundness and cross-section height were larger for the cod. We conclude that the computer vision method can be used effectively for automated monitoring of changes in 2D and 3D shape and size of fish fillets during rigor mortis and ice storage. In addition, it can be used for grading of fillets according to uniformity in size and shape, as well as measurement of fillet yield measured in thickness. The methods are accurate, rapid, nondestructive, and contact-free and can therefore be regarded as suitable for industrial purposes.     

Potential Application of the Electronic Nose for Quality Assessment of Salmon Fillets Under Various Storage Conditions

ABSTRACT: The feasibility of using an electronic nose (AromaScan^TM) to assess seafood quality was studied with salmon fillets stored at -20, 4, and 10 °C for 14 d. AromaScan mappings of these fillets were compared to their timerelated changes in microbial counts, histamine contents, and sensory panel evaluations. Fillets stored at 10 °C had respective bacterial counts of 8.90 and 9.06 log¹⁰ CFU/g after 7 and 9 d. The mappings for the 10 °C fillets were separated from those of fresh fillets by Day 3, and continued to separate further as storage time increased. An electronic nose can be used as an assisting instrument to a sensory panel in evaluating seafood quality.     

Effects of Rested Harvesting on Muscle Metabolite Concentrations and K-Values in Chinook Salmon (Oncorhynchus tshawytscha) Fillets during Storage at 15 °C

Abstract: Improvement of harvesting procedures in aquaculture may also improve the quality and storage properties of the fish. The use of an anesthetic allows fish to be harvested with reduced stress and exhaustion, which affect fillet properties. We report here on the effects of rested harvesting on the postharvest metabolic profiles and K-values in Chinook salmon (Oncorhynchus tshawytscha) fillets stored near to the fish's acclimation temperature at 15 °C for 36 h. Fresh rested fillets were obtained by anesthesia with AQUI-S™. They had high cut surface pHs (7.63) and high concentrations of adenosine triphosphate (ATP) and creatine phosphate (3.75 and 8.73 μmol g⁻¹ respectively), which depleted over 12 h. In contrast, fresh exhausted fillets had low cut surface pHs (6.66) and ATP and creatine phosphate were depleted. Adenosine diphosphate (ADP) and β-nicotinamide adenine dinucleotide (NAD⁺) concentrations also remained significantly higher during the first 12 h of storage in rested fillets. In fresh rested fillets inosine monophosphate (IMP) concentrations reached maximum after 12 h storage (4.78 μmol g⁻¹), whereas maximum IMP concentrations occurred immediately postharvest in the exhausted fillets (6.42 μmol g⁻¹). After 36 h storage, K-values in exhausted fillets reached 52.11% compared to 19.27% in rested fillets. Rested harvesting of Chinook salmon improved the fillets’ metabolic potential postharvest, extending metabolite depletion times, changing IMP concentrations and reducing K-values. Practical Application: This study shows that an improved metabolic potential is maintained in salmon fillets from fish harvested in a rested state (that is, with no stress and exhaustion) using an isoeugenol based anesthetic (AQUI-S™). Improved understanding of postharvest metabolic function may help to improve quality and storage properties of high value fish tissues.     

A Feasibility Study on the Use of Near Infrared Spectroscopy for the Authentication of Depurated Salmon Fillets

Some species of actinomycetes, fungi, and blue-green algae produce semivolatile off-flavor compounds responsible for earthy-musty odorants in water from aquaculture facilities and tend to bioaccumulate within fish flesh. Although these off-flavor compounds are harmless to human health, high levels within fish tissue lead to an undesirable taste leading to an unmarketable consumption quality. Preharvest processes such as depuration can be used to eliminate most of these off-flavor compounds and ultimately enhance salmon quality. This study examined the potential of near infrared spectroscopy (NIRS) to discriminate depurated from nondepurated salmon fillets (n?=?62). Partial least squares discriminant analysis based on NIR spectra correctly classified 100 % of non-depurated and depurated salmon fillets. The successful classification was likely a consequence of statistically significant differences in the content of off-flavor compounds between both samples, which could have been detected by NIR spectra. Thus, NIRS is a fast, inexpensive, solvent-free, and non-destructive technology that can be used for the authentication of salmon with enhanced quality for marketing purposes.