Effects of Salt-curing Procedure and Smoking Temperature on Astaxanthin Stability in Smoked Salmon

ABSTRACT: The effects of salting method (injection salting compared with dry salting), smoking temperature (20°C compared with 30°C), and storage (chilled storage compared with no storage) on astaxanthin retention, surface coloration (CIE1994 L * a * b *), and process yields of cold-smoked Atlantic salmon ( Salmo salar ) fillets was investigated. An overall loss of 13% astaxanthin was observed when correcting for weight changes. Astaxanthin retention was 6.0% higher after smoking at 30°C than at 20°C ( P < 0.01). A significant decrease in astaxanthin retention (4%) was observed after chilled storage of vacuum-packaged fillets at 1°C ( P < 0.05). Salt curing was quantitatively more important to astaxanthin loss than smoking temperature and storage. Salting method did not affect astaxanthin retention, but its concentration was reduced significantly more by injection salting than with dry salting ( P < 0.01). A higher overall color change (AE) was observed for dry-salted compared with injection-salted fillets ( P < 0.001) and for fillets smoked at 30°C compared with 20°C ( P < 0.05), and this coincided with a high variability in the colorimetric parameters in these groups. Higher product yields were obtained by injection salting compared with dry salting (10%) and after smoking at 20°C compared with 30°C (2%), P < 0.001. It is concluded that choice of processing technology may have substantial impact on important quality parameters such as color stability and variation in cold-smoked Atlantic salmon.     

Effect of Salt, Smoke Compound, and Temperature on the Survival of Listeria monocytogenes in Salmon during Simulated Smoking Processes

ABSTRACT:  The objectives of this study were to examine and develop a model to describe the survival of  Listeria monocytogenes  in salmon as affected by salt, smoke compound (phenol), and smoking process temperature. Cooked minced salmon containing selected levels of salt (0%, 2%, 4%, and 6%) and smoke compound (0, 5, 10, and 15 ppm phenol) were inoculated with a 6-strain mixture of  L. monocytogenes  to an inoculum level of 6.0 log₁₀ CFU/g. The populations of  L. monocytogenes  in salmon during processing at 40, 45, 50, and 55 °C that simulated cold- and hot-smoking process temperatures were determined, and the effects of salt, phenol, and temperature on the survival of  L. monocytogenes  in salmon were analyzed and described with an exponential regression. At 40 °C, the populations of  L. monocytogenes  in salmon decreased slightly with inactivation rates of <0.01 log₁₀ CFU/h, and at 45, 50, and 55 °C, the inactivation rates were 0.01 to 0.03, 0.15 to 0.30, and 2.8 to 3.5 log₁₀ CFU/h, respectively. An exponential regression model was developed and was shown to closely describe the inactivation rates of  L. monocytogenes  as affected by the individual and combined effects of salt, phenol, and smoking process temperature. Temperature was the main effector in inactivating  L. monocytogenes  while salt and phenol contributed additional inactivation effects. This study demonstrated the inactivation effects of salt, smoke compound, and temperature on  L. monocytogenes  in salmon under a smoking process. The data and model can be used by manufacturers of smoked seafood to select concentrations of salt and smoke compound and alternative smoking process temperatures at 40 to 55 °C to minimize the presence of  L. monocytogenes  in smoked seafood.     

Influence of Salmon Provenance and Smoking Process on Muscle Functional Characteristics

ABSTRACT: Ocean-ranched and farm-reared Atlantic salmon were compared on the basis of compositional and functional/mechanical properties of the raw and the corresponding smoked muscle. Several procedures based on different salting methods (brine and dry salting) and smoking temperature (20 °C and 30 °C) were tested, as well as an electrostatic smoking method. Also, raw material samples were studied without and with frozen storage (-20 °C) for 30 d prior to salting/smoking, and the effect of frozen storage on the smoked muscle was evaluated. The electrostatic method induced considerably lower shear force values than the other smoking treatments. Ocean-ranched salmon were more susceptible to protein aggregation and loss of binding properties (water and fat) than farmed fish as a consequence of frozen storage of the raw material or smoking treatment.     

Lipid Oxidation Is Inhibited by Isoeugenol Exposure in Chinook Salmon (Oncorhynchus Tshawytscha) Fillets during Storage at 15 °C

ABSTRACT:  The method of harvest for farmed fish and the postharvest tissue metabolism can have a significant effect on the quality and storage stability of the resulting fillets. We have examined the effects of rested harvesting and isoeugenol exposure on tissue oxidation and the loss of tissue antioxidants in fillets of chinook salmon ( Oncorhyncus tshawytscha ) during storage at a normal metabolic temperature of 15 °C. Isoeugenol is a lipid soluble phenolic antioxidant used as an anesthetic in the aquaculture industry (AQUI-S™). Fillets from salmon harvested in rested and exhausted physiological states with and without isoeugenol were prepared and stored in air at 15 °C for 96 h. Exposure to isoeugenol resulted in significantly decreased late-stage lipid peroxidation (TBARS) levels in the fillets during storage regardless of the harvest method. Protein carbonyl concentrations increased 73% in the fillets during storage (from 406 to 703 nmol/g wet weight) and were not affected by the harvest method. Fillet vitamin C concentrations decreased 92% (from 49 to 4 nmol/g wet weight) but were also not affected by the harvest method. Although significant late-stage lipid oxidation was observed with exhausted harvesting, no significant vitamin E loss was observed in any of the fillets during storage. Our results show that rested harvesting of chinook salmon does not affect their oxidative stability immediately postharvest and that isoeugenol can function as an antioxidant in fish fillets as it prevented late-stage lipid oxidation.     

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     

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.     

Liquid holding capacity,texture and fatty acid profile of smoked fillets of Atlantic salmon fed diets containing fish oil or soybean oil

This study evaluates the effects of dietary vegetable oils on the liquid-holding capacity, texture properties and fatty acid composition of Atlantic salmon fillets. Three diets containing 100% of fish oil (FO), 100% of soybean oil (SO) or a 50/50 mixture of the two oils (FO/SO) as oil dietary source, were fed to triplicate groups of salmon. After slaughter, a third of the fish were studied fresh while the rest of fish were smoked and stored at two temperatures (4 °C or 14 °C) for 5 or 15 days. The liquid-holding capacity and the texture of fresh and smoked fillets were not significantly affected by dietary oil whereas the smoking yield increased with the inclusion of soybean oil. The fatty acid profile of fresh and smoked fillets reflected these of the diets, and no selective loss of fatty acids was observed after smoking and after storage. On the other hand, increased storage time and storage temperature reduced strongly the liquid-holding capacity of all smoked salmon particularly obvious as increased fat loss, irrespective of the diets. This study showed that an increase in storage time and temperature of smoked fillets of Atlantic salmon affected the liquid-holding capacity, irrespective of the diets.     

Effect of Modified Atmosphere Packaging and Superchilled Storage on the Microbial and Sensory Quality of Atlantic Salmon (Salmo salar) Fillets

ABSTRACT: Fresh Atlantic salmon fillets packaged under modified atmosphere (MA) (CO²:N² 60:40) and air was stored at superchilled (-2 °C) and chilled (+4 °C) temperatures. Changes in sensory scores, microbial growth, headspace gas composition, water loss, and pH were monitored during 24 d of storage. The superchilled MA packaged salmon maintained a good quality, with negligible microbial growth (<1000 colony-forming units [CFU]/g) for more than 24 d based on both sensory and microbial analyses (aerobic plate count, H2S-producing, and psychrotrophic bacteria). Superchilled salmon in air had a 21-d sensory shelf life, whereas MA and air-stored fillets at chilled conditions was spoiled after 10 d and 7 d, respectively.     

A Comparison Between E-Beam Irradiation and High-Pressure Treatment for Cold-Smoked Salmon Sanitation: Shelf-Life, Colour, Texture and Sensory Characteristics

The effect of electron beam irradiation and high-pressure treatment on the characteristics of cold-smoked salmon during refrigerated storage at 5 °C was investigated. Irradiation at 1–4 kGy and high-pressure treatments at 450 MPa for 5–25 min reduced total viable counts and delayed microbial growth. Irradiation induced a slight decrease in redness (a*), whereas high-pressure treatment resulted in a brighter (L*) appearance of smoked salmon. Higher values of hardness and shear strength were recorded for pressurized samples. Total biogenic amine concentration in smoked salmon held for 20 days at 5 °C was lowered by 81 % in samples irradiated at 2 kGy, and by 46 % in samples pressurized at 450 MPa for 25 min. Smoked salmon irradiated at 1 or 2 kGy had negligible sensory (appearance, odour and flavour) alterations, but lower sensory preferences in the rank order test were observed for 3 and 4 kGy samples. Pressurization for 5 min at 450 MPa induced moderate sensory changes, which were more marked after 15 or 25 min at 450 MPa. These results point to the usefulness of E-beam radiation at 1.5 kGy to assure a safe product of sensory characteristics similar to those of untreated smoked salmon.     

Stabilizing Smoked Salmon (Oncorhynchus gorbuscha) Tissue after Extraction of Oil

ABSTRACT: Alaska salmon oils are rich in n-3 polyunsaturated fatty acids and are highly valued by the food and pharmaceutical industries. However, the tissue that remains after oil extraction does not have an established market. Discarded pink salmon (Oncorhynchus gorbuscha) tissues were preserved using a combination of smoke-processing and acidification with lactic acid bacteria (LAB). All samples were analyzed for moisture, protein, ash, and lipid contents. Bacterial cell counts, pH, and lactic acid concentrations were recorded as a measure of LAB viability. Neither raw nor smoked salmon were free from spoilage during 60 d of storage. Only fermented samples successfully stabilized below pH 4.7, while retaining lactic acid concentrations over 15 g/L during storage. When smoked, fermented salmon head tissues were dried, the pH of the resulting high-protein “cracker” was significantly lower than when crackers were prepared only from the smoked (but not fermented) salmon material. Both cracker varieties retained valuable polyunsaturated fatty acids. This research suggests that salmon-head tissues discarded after oil extraction represent a good source of protein and high-value fatty acids in a shelf-stable form. Practical Application: Alaska salmon oils are rich in n-3 polyunsaturated fatty acids and are highly valued by the food and pharmaceutical industries. However, the tissue that remains after oil extraction does not have an established market. Material produced from salmon tissue discarded after oil extraction may represent a valuable resource for preparing high-protein crackers and other fish-based food products. In addition to providing a unique smoke-flavoring, the smoked, fermented fish material may also impart antioxidant factors thereby extending the shelf life of the product.     

Prediction of Microbial and Sensory Quality of Cold Smoked Atlantic Salmon (Salmo salar) by Electronic Nose

ABSTRACT: Quality changes of cold smoked salmon from 4 different smokehouses in Europe were monitored by a prototype gas-sensor array system, the FishNose. Samples were stored in different packaging (vacuum and Modified Atmosphere Packaging [MAP]) for up to 4 wk under controlled storage conditions at 5 °C and 10 °C. Quality criteria based on sensory attributes (sweet/sour, off, and rancid odor), and total viable counts and lactic acid bacteria counts were established and used for classification of samples based on the responses of the FishNose. The responses of the gas-sensors correlated well with sensory analysis of spoilage odor and microbial counts suggesting that they can detect volatile microbially produced compounds causing spoilage odors in cold-smoked salmon during storage. The system is therefore ideal for fast quality control related to freshness evaluation of smoked salmon products. Partial least squares (PLS) regression models based on samples from single producer showed better performance than a global model based on products from different producers to classify samples of different quality.     

Computer Vision and Stereoscopy for Estimating Firmness in the Salmon (Salmon salar) Fillets

The computer vision and a stereoscopy technique were used to characterize and detect changes in the capacity of the salmon fillet surface to recover its original form after a constant weight was applied. A curvature index (associated to fillet firmness) calculated by means of 3D information data obtained with the stereoscopy technique from the fat stripe on the fillets was estimated over 6 months and was suggested as a characteristic of the recovery property of the fresh salmon fillet surface. Simultaneously, instrumental firmness using a LFRA1500 texture was measured. The values for the fresh salmon fillet measurement curvature index during a period of 6 months were established in the range of 0.05 and 0.10 (dimensionless), and this value was used in the experiments to represent fresh salmon fillets. Changes in the curvature index (associated with similar changes in firmness) for salmon fillet surface treated with enzymes (pepsin and papain) were registered on the second day during storage at 2 °C. In general, stereoscopy is a technique that can be used on salmon fillets to detect changes in the recovery properties of the salmon fillet surface and to determine when salmon fillets can be classified as a fillet that has not been processed with enzymes.     

EFFECT OF SMOKE SOURCES ON QUALITY AND STORAGE STABILITY OF CATFISH FILLET (Clarias macrocephatus Gunther)

The effect of smoke sources, bagasse and coconut husk, on the chemical composition, acceptability and quality changes of catfish fillets was investigated. Catfish smoked with either of the sources had similar compositions. Catfish fillets smoked with coconut husk attained significantly higher preference scores for color but odor scores were lower compared with those smoked with bagasse (p < 0.05). However, no significant differences in other attributes were observed for fillets smoked by the two different kinds of starting material. Smoked fillets showed lower TBA values, ammonia content, aerobic plant count (APC), yeast and mold than the control throughout 10 weeks of storage at 4C. For the smoked fillets, nonenzymatic browning was prevalent.     

Effect of filtered wood smoke treatment on chemical and microbial changes in mahi mahi fillets

ABSTRACT:  A study was performed to investigate the effect of filtered wood smoke processing on quality and safety of mahi mahi compared to no treatment. Skinless mahi mahi fillet portions were either treated with filtered smoke (FS) or left untreated for 24 h, followed by either (a) aerobic storage at 4 °C for 8 d or (b) freezing for 30 d (–25 °C) followed by thawing and aerobic storage at 4 °C for 8 d. Results show that treating mahi mahi fillets with FS increased ( P < 0.05) a * values (redness) of the muscle and stabilized it during frozen storage. The redness did, however, decay ( P < 0.05) rapidly on cold storage for both defrosted and fresh filtered-smoke-treated products, and reached initial (presmoking) redness levels in 2 d. The FS process overall significantly ( P < 0.05) improved microbial stability of the product. Stability toward lipid oxidation was also significantly ( P < 0.05) increased for the FS products compared to untreated products, particularly after defrosting. Sensory studies supported the microbial and lipid oxidation findings, showing that products treated with FS were better accepted and had increased ( P < 0.05) shelf life over the untreated products. The shelf life was, however, compromised when microbial levels increased; that is, the process did not mask microbial spoilage; the spoilage did become evident in the sensory trials.     

光照和温度对草鱼和三文鱼鱼肉贮藏品质的影响

采用4、10(无光照)、10(5 000 lx)、25℃条件,同时贮藏草鱼鱼片(除去红肉)和三文鱼鱼片,研究光照和温度对草鱼和三文鱼贮藏品质的影响。结果表明,草鱼和三文鱼贮藏过程中pH值、挥发性盐基氮(total volatile basic nitrogen,TVB-N)值、硫代巴比妥酸(thiobarbituric acid,TBA)值和色差变化差异显著(P0.05),且菌落总数(total viable count,TVC)、pH值、TVB-N值、TBA值、色差、ATP分解产物(adenosine triphosphate-related decomposition products)K值均随着贮藏时间的延长而增加。光照(5 000 lx)对于草鱼、三文鱼贮藏过程中的pH值变化、TBA值变化影响显著(P0.05),能使鱼肉中pH值增加量高于避光保存,促进光氧化,提高TBA值增加速率,而对于TVC、TVB-N值、K值、色差变化影响不显著(P0.05)。贮藏温度的差异(4、10℃)对两种鱼肉品质变化都有显著影响(P0.05)。     

Physicochemical,sensorial and textural characteristics of liquid‐smoked salmon (Salmo salar) as affected by salting treatment and sugar addition

The effect of salting method, dry salting (DS), brine salting (BS), brine salting with sucrose addition (BSS) or dry salting with sucrose addition (DSS) on the quality of Atlantic salmon treated with a liquid smoke flavouring was investigated over a 45‐day storage period. Sugar‐added samples were the ones with the significantly lowest values for TBARS (β₀, DS = 0.09^b; BS = 0.18^a; DSS = 0.07^c; BSS = 0.07^c). BSS and DSS fillets showed faster production rates of trimethylamine (TMA), 0.57 and 1.46, than the DS and BS fillets, 0.81 and 1.19, respectively. The DS and DSS fillets showed long delay periods before the TMA concentration started to increase (16.18; 20.60), and 90% of the panellists preferred these to BS or BSS fillets. In fact, only the BSS fillets were rejected during the storage, after 34 days; and the fillets with the most overall desirable characteristics at the end of the storage period were those of the DSS group.     

Textural and physicochemical changes in salmon (Salmo salar) treated with commercial liquid smoke flavourings

The textural and physicochemical properties of fillets of farmed Atlantic salmon (Salmo salar) treated with two commercial liquid smoke flavourings (LS1 and LS2) were examined after 15, 30 and 45 days of storage at 2 °C in oxygen impermeable bags. Salmon flesh treated with LS1 was characterized by high water-soluble protein, fat and moisture contents, plus low hardness, fracturability, gumminess and chewiness, and a low alkali-insoluble protein content. These characteristics were similar to those of control salmon (not treated with liquid smoke flavouring). Storage time changed these properties similarly in both. Salmon flesh treated with LS2 was characterized by high hardness, fracturability, gumminess, chewiness and alkali-insoluble protein levels, plus low water-soluble protein, fat and moisture contents. Storage time appeared to have a far less important effect on salmon flesh treated with LS2.     

Influence of processing steps in cold-smoked salmon production on survival and growth of persistent and presumed non-persistent Listeria monocytogenes

Cold-smoked salmon is a ready-to-eat product in which Listeria monocytogenes sometimes can grow to high numbers. The bacterium can colonize the processing environment and it is believed to survive or even grow during the processing steps. The purpose of the present study was to determine if the steps in the processing of cold-smoked salmon affect survival and subsequent growth of a persistent strain of L. monocytogenes to a lesser degree than presumed non-persistent strains. We used a sequence of experiments increasing in complexity: (i) small salmon blocks salted, smoked or dried under model conditions, (ii) fillets of salmon cold-smoked in a pilot plant and finally, (iii) assessment of the bacterial levels before and after processing during commercial scale production. L. monocytogenes proliferated on salmon blocks that were brined or dipped in liquid smoke and left at 25 degrees C in a humidity chamber for 24 h. However, combining brining and liquid smoke with a drying (25 degrees C) step reduced the bacterium 10-100 fold over a 24 h period. Non-salted, brine injected or dry salted salmon fillets were surface inoculated with L. monocytogenes and cold-smoked in a pilot plant. L. monocytogenes was reduced from 10(3) to 10-10(2) CFU/cm(2) immediately after cold-smoking. The greatest reductions were observed in dry salted and brine injected fillets as compared to cold-smoking of non-salted fresh fillets. Levels of L. monocytogenes decreased further when the cold-smoked fish was vacuum-packed and stored at 5 degrees C. A similar decline was seen when inoculating brine injected fillets after cold-smoking. High phenol concentrations are a likely cause of this marked growth inhibition. In a commercial production facility, the total viable count of salmon fillets was reduced 10-1000 fold by salting, cold-smoking and process-freezing (a freezing step after smoking and before slicing). The prevalence of L. monocytogenes in the commercial production facility was too low to determine any quantitative effects, however, one of nine samples was positive before processing and none after. Taken together, the processing steps involved in cold-smoking of salmon are bactericidal and reduce, but do not eliminate L. monocytogenes. A persistent strain was no less sensitive to the processing steps than a clinical strain or strain EGD.     

Injection-salting of pre rigor fillets of Atlantic salmon (Salmo salar)

ABSTRACT:  The effects of temperature (−1, 4, and 10 °C), brine concentration (12% and 25% NaCl), injection volumes, and needle densities were investigated on fillet weight gain (%), salt content (%), fillet contraction (%), and muscle gaping in pre rigor brine-injected fillets of Atlantic salmon ( Salmo salar ). Increased brine concentration (12% to 25%) significantly increased the initial (< 5 min after injection) and final contraction (24 h after injection) of pre rigor fillets. Increased brine concentration significantly reduced weight gain and increased salt content but had no significant effect on muscle gaping. The temperatures tested did not significantly affect weight gain, fillet contraction, or gaping score. Significant regressions ( P < 0.01) between the injection volume and weight gain (range: 2.5% to 15.5%) and salt content (range: 1.7% to 6.5%) were observed for injections of pre rigor fillets. Double injections significantly increased the weight gain and salt content compared to single injections. Initial fillet contraction measured 30 min after brine injection increased significantly ( P < 0.01) with increasing brine injection volume but no significant difference in the fillet contraction was observed 12 h after brine injection (range: 7.9% to 8.9%). Brine-injected post rigor control fillets obtained higher weight gain, higher salt content, more muscle gaping, and significantly lower fillet contraction compared to the pre rigor injected fillets.
Injection-salting is an applicable technology as a means to obtain satisfactory salt contents and homogenously distribute the salt into the muscle of pre rigor fillets of Atlantic salmon before further processing steps such as drying and smoking.     

Reducing levels of Listeria monocytogenes contamination on raw salmon with acidified sodium chlorite

The antimicrobial activity of acidified sodium chlorite (ASC) against Listeria monocytogenes in salmon was studied. Raw salmon (whole fish and fillets) inoculated with L. monocytogenes (10(3) CFU/cm2 or 10(4) CFU/g) were washed with ASC solution (50 ppm) for 1 min and stored at -18 degrees C for 1 month (whole salmon) or in ice for 7 days (fillets). L. monocytogenes populations were determined for whole salmon after frozen storage and for fillets on days 1, 3, 5, and 7 of storage. A wash with ASC solution followed by ASC glazing did not reduce L. monocytogenes on the skin of whole salmon during frozen storage. However, the wash resulted in an L. monocytogenes reduction of 0.5 log CFU/g for salmon fillets. The populations of L. monocytogenes in fillets increased slowly during ice storage, but the growth of these populations was retarded by ASC ice. By day 7, the populations were 0.25 log units smaller in fillets stored in ASC ice and 0.62 log units smaller in fillets that had been washed with ASC solution and stored in ASC ice than in control fillets. Treatment with ASC also reduced total plate counts (TPCs) by 0.43 log CFU/cm2 on the skin of whole salmon and by 0.31 log CFU/g in fillets. The TPCs for skin decreased during frozen storage but increased gradually for fillets stored at 5 degrees C or in ice. However, TPCs of ASC-treated samples were lower than those for controls at any point during the study. Washing with ASC solution significantly (P < 0.05) reduced TPCs on the skin of whole salmon and in fillets, as well as L. monocytogenes in fillets. The antimicrobial activity of ASC was enhanced when salmon was washed with ASC solution and stored in ASC ice.