Smoked Salmon Products Research Articles

Microbial consortia in commercial salmon products: A comparative study using cultivation-dependent and high-throughput sequencing approaches

Despite the widespread consumption of salmon products, an all-round microbiological survey on fresh salmon and smoked salmon products sold on the market directly to consumers remains to be undertaken. The present study conducted a comprehensive microbial investigation employing both conventional cultivation-based techniques and 16S rRNA amplicon sequencing. A total of 120 fresh salmon and 95 smoked salmon products were systematically collected across all four seasons (spring, summer, fall, and winter), accompanied by temperature assessments of each product’s interior. The average aerobic plate counts for fresh salmon and smoked salmon were 3.63 log and 1.36 log CFU/g, respectively, and the highest seasonal concentrations occurred in summer. The average coliform count was higher in fresh salmon (1.50 log CFU/g) than in smoked salmon products (1.12 log CFU/g). Although smoked salmon exhibited CFU counts similar to those of fresh salmon according to culture-based methods, 16S sequencing unveiled a distinct microbial composition. Photobacterium and Pseudomonas, recognized as major spoilage-related microorganisms, were the predominant genera in all products, but especially in fresh salmon. Smoked salmon exhibited diverse variations in bacterial composition compared to fresh salmon. Three types of lactic acid bacteria—Leuconostoc, Lactobacillus, and Lactococcus—were found to be significantly more abundant in smoked salmon than in fresh salmon. The outcomes of this study contribute to an enhanced understanding of retail salmon products, shedding light on crucial areas for investigation and suggesting potential interventions regarding both sales and production of salmon products.

Prolonged multi‐country outbreak of Listeria monocytogenes ST1607 linked to smoked salmon products

Prolonged multi‐country outbreak of Listeria monocytogenes ST1607 linked to smoked salmon products

Fatty Acid Composition of Commercial Smoked Salmon Products

In this study, the fatty acid composition of smoked salmon fillets sold in grocery stores in Türkiye was investigated. Gas chromatography (GC) was used to determine fatty acid composition from extracted lipid. The main saturated fatty acids observed in smoked salmon samples were myristic acid (C14:0), palmitic acid (C16:0) and stearic acid (C18:0); monounsaturated fatty acids were palmitoleic acid (C16:1), oleic acid (C18:1n9), and vaccenic acid (C18:1n7); polyunsaturated fatty acids (PUFA) were linoleic acid (C18:2n6), eicosapentaenoic acid (EPA, C20:5n3) and decosahexaenoic acid (DHA, C22:6n3). Among the monounsaturated fatty acids, oleic acid was found to be the fatty acid with the highest value. Oleic acid amounts were found to vary between 27.22% and 35.52%. PUFA values in smoked salmon fillet groups were determined as 27.77%, 27.49%, 32.94% and 30.62%. The highest EPA value was determined in F1 group with 4.29% and the lowest value was determined in F2 group with 2.07%. DHA amounts were between 11.74% and 6.22%. The ratio of Σn6/Σn3 was between 0.80 (F4 group) and 1.16 (F2 group). As a result, it was concluded that the smoked fish fillets examined had high nutritional quality in terms of fatty acids. Among the groups, especially F3 and F4 groups were found to have rich content in terms of PUFA and Σn3 values.

Identification and serotyping of Listeria monocytogenes, isolated from various salmon products, sold in retail market in Lithuania.

Cold smoked salmon products (belly flaps, pieces, fillet, and loin) obtained from the retail market in Lithuania were tested for the presence of L. monocytogenes. It was found that contamination of the cold smoked fish products with Listeria spp. depends on the type of the product. Contamination with listeria in salmon belly flaps was 7.5 times higher than in the loin (P<0.05), 1.8 times higher than in the pieces (P<0.05) and 30 times higher than in the fillet (P<0.05). Microbiological analysis showed that 32.5% (P<0.05) of the fish product samples were infected with L. monocytogenes, while multiplex PCR confirmed 31.25% positive samples (P<0.01). According to the study results, L. monocytogenes strains were divided into two serotypes: 4b (94.6%) and 1/2a (5.4%). High contamination of the products with Listeria spp. showed that cold smoked salmon products, sold in local market, can be a reason of human listeriosis in Lithuania.

Antimicrobial activity of 405nm light-emitting diode (LED) in the presence of riboflavin against Listeria monocytogenes on the surface of smoked salmon.

This study investigated the antimicrobial activity of 405nm light-emitting diode (LED) with and without riboflavin against Listeria monocytogenes in phosphate buffered saline (PBS) and on smoked salmon at different storage temperatures and evaluated its impact on food quality. The results show that riboflavin-mediated LED illumination in PBS 25°C significantly inactivated L. monocytogenes cells by 6.2 log CFU/mL at 19.2J/cm2, while illumination alone reduced 1.9 log CFU/mL of L. monocytogenes populations at 57.6J/cm2. L. monocytogenes populations on illuminated smoked salmon decreased by 1.0-2.2 log CFU/cm2 at 1.27-2.76kJ/cm2 at 4, 12, and 25°C, regardless of the presence of riboflavin. Although illumination with and without riboflavin caused the lipid peroxidation and color change in smoked salmon, this study demonstrates the potential of a 405nm LED to preserve the smoked salmon products, reducing the risk of listeriosis.

Controlling Listeria monocytogenes in Cold Smoked Salmon with the Antimicrobial Peptide Salmine.

Listeria monocytogenes (LM) is a major safety concern for smoked salmon producers, as it can survive both the brining and smoking process in cold smoked salmon production. Salmine is a cationic antimicrobial peptide derived from the milt of salmon that has been shown to inhibit the growth of LM in vitro. Commercialization of this peptide would add value to a waste product produced when raising salmon. The purpose of this study was to determine the anti-listeria activity of salmine in smoked salmon by measuring the viable counts of LM over time. Cold smoked salmon was treated with a salmine solution or coated with agar or k-carrageenan films incorporating salmine to maintain a high surface concentration of the antimicrobial. Samples were then inoculated with approximately 1.0×10(3) cells of LM. The viable counts were then enumerated throughout 4 wk at 4 °C storage. It was found that 5 mg/g salmine delayed the growth of LM on smoked salmon. These samples had significantly (P<0.05) lower LM counts than on the untreated samples on days 13 and 22. Edible films did not significantly (P > 0.05) improve the antimicrobial efficacy of salmine. The peptide combined with biopolymers also had lower antimicrobial activity in vitro when compared to salmine alone. These results suggest there is potential for salmine to be used as a natural hurdle to inhibit growth of LM due to post process contamination; however, future investigations for extending this effect throughout the shelf life of smoked salmon products are warranted.

Outbreak of Salmonella Thompson in the Netherlands since July 2012

An ongoing outbreak of salmonellosis due to Salmonella Thompson is affecting the Netherlands. Between 2 August and 19 October 2012, 866 cases were confirmed. Their median age was 44 years (range: 0-95 years), 63% were female and 36% were hospitalised. A matched case-control study suggested smoked salmon as the vehicle. Salmonella Thompson was confirmed in four of nine batches of smoked salmon from one producer. A recall of all concerned smoked salmon products was executed starting end of September.

Shelf‐life of vacuum packed Alaskan, Scottish and Norwegian cold‐smoked salmon available on the Italian market

SummaryFourteen vacuum packed cold smoked salmon products of different origin purchased in Italian retail were analysed at about half shelf‐life (HSL) and at the expiry date (ED). On ED, eight on fourteen samples had concentration of total volatile basic nitrogen (TVBN) indicating spoilage (values &gt;40 mg N/100 g and up to 71.3 mg N/100 g) and only five samples were not rancid (thiobarbituric acid reactive substances, TBARS &lt;8 nmol/g). Total psychrotrophic count (TPC) at HSL was acceptable (&lt;106 CFU/g) in most samples; at ED, in 13 samples, TPC was very high (range 1.2 × 106– 6.0 × 108 CFU/g) and Lactobacilli were the most representative bacteria. No pathogens were detected. Significant negative differences in declared weight (over 8%) were determined in nine samples. The two months shelf‐life attributed to smoked salmon marketed in Italy proved to be, generally, too long and the consumer is at risk to buy a product in early stage of spoilage.

Volatile compounds suitable for rapid detection as quality indicators of cold smoked salmon (Salmo salar)

Volatile compounds in cold smoked salmon products were identified by gas chromatography to study their suitability for rapid detection as indicators to predict sensory quality evaluated by quantitative descriptive analysis. Smoked salmon odour contributed by guaiacol, boiled potato- and mushroom-like odours characteristic for fish lipid degradation and sweet odours associated with the microbial metabolites 3-methyl-butanal and 3-hydroxybutanone were the most intense odours. Other key volatiles were present in high levels but contributed less to the odours. These included furan-like compounds originating from the smoking, spoilage compounds like ethanol, 3-methyl-1-butanol, 2-butanone, and acetic acid along with oxidatively derived compounds like 1-penten-3-ol, hexanal, nonanal and decanal. Partial least square regression models based on data from storage studies of cold smoked salmon from Iceland and Norway verified that selected key volatile compounds performed better as predictors to explain variation in sensory attributes (smoked, sweet/sour rancid and off odour and flavour) than traditional chemical and microbial variables.

Effect of superchilled storage on the freshness and salting behaviour of Atlantic salmon ( Salmo salar) fillets

The aim of this work has been to evaluate the effect of superchilled storage compared with ice and frozen storage on the quality of raw material and subsequent behaviour during processing of lightly salted salmon ( Salmo salar), as the first step of smoked salmon production. Physicochemical parameters used as quality indicators were α-glucosidase activity, protein denaturation and degradation (as changes in protein solubility, SDS–PAGE and free amino acids), texture attributes, and mass transfer phenomena during salting. The results obtained for the raw material within the storage range studied (until 16 days) allowed us to conclude that salmon superchilled for 9 days behaved as salmon stored on ice for 2 days with regard to hardness, protein solubility and free amino acids. In general, salting minimises the effect of the different storage methods. Superchilling for 9 days obtained the highest process yield, indicating that this method is a good way to preserve freshness of the raw material before processing.

Comparison of Listeria monocytogenes strain types in Irish smoked salmon and other foods

An investigation of Listeria monocytogenes in Irish retail smoked salmon products and other unrelated food products was undertaken. Serotyping and genotyping methods were applied. Twenty-six L. monocytogenes isolates cultured from ready-to-eat smoked salmon and an additional 20 L. monocytogenes isolates from various commercially available food products (other than smoked salmon) were compared. Four serotypes, 12 ribotypes, 12 amplified fragment length polymorphism (AFLP) types and 17 pulsed-field gel electrophoresis (PFGE) types were identified among the 46 isolates studied. Genotyping identified a single dominant strain that accounted for 65% of those cultured from smoked salmon and this strain was present in product obtained from three out of five of the manufacturers surveyed. When compared to the food products obtained from a variety of sources, those from smoked salmon appeared to cluster as a single group. In Irish smoked salmon this strain may have adapted, and be capable of persisting in this food product. All isolates were grouped into genetic lineages based on their EcoR1 ribotypes. The attendant risk to public health following consumption of these foods is discussed.

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

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.

Rapid control of smoked Atlantic salmon ( Salmo salar) quality by electronic nose: Correlation with classical evaluation methods

A prototype solid-state-based gas-sensor array system including a gas sampling unit, the FishNose, for direct quality measurements of smoked salmon has been developed. Quality changes of smoked salmon during storage were monitored by the FishNose and compared with the results of traditional sensory, chemical, and microbial measurements. Gas-sensor selection was optimized for the detection of changes in the very volatile compounds mainly representing microbial metabolism during spoilage. Sensor readings of repeated measurements of calibration samples showed a repeatability for the six sensors of the array of 6.4% (±1.4%), and for repeated measurements of fish samples the repeatability was 4.3% (±2.6%) without purge of the system between the measurements. The system was further tested on-site in a smoked salmon production plant. Due to varying ambient air conditions at the production plant during the measurements, the sensor readings had to be corrected for by subtracting the sensor readings for the background air. High classification rates were obtained of 95 and 93% for good and bad samples, respectively. This work demonstrated that the FishNose, equipped with an application specific sampling unit, was suitable for monitoring quality changes occurring during storage of smoked salmon and that the system was able to predict the quality related attributes like sweet/sour and off odour, and microbial counts.

Effects of divercin V41 combined to NaCl content, phenol (liquid smoke) concentration and pH on Listeria monocytogenes ScottA growth in BHI broth by an experimental design approach.

To investigate the main effects and interactions of different factors : divercin V41 (0-4 ng ml(-1)), NaCl content (0.5-5.5% w v(-1)), phenol (liquid smoke) concentration (0-8 ppm), and pH (5.5-7.5) on Listeria monocytogenes ScottA growth. Experiments were carried out in BHI broth using a central composite design. Divercin V41 (div41), NaCl content and pH were found to be the most influential factors whereas phenol concentration in liquid smoke had no effect on L. monocytogenes ScottA growth in our experimental domain. The combined effects of div41, NaCl content and pH decreased L. monocytogenes ScottA maximum specific growth rate (mu(max)) from 0.34 to 0.01 h(-1) and led to a significant increase in lag time (t(lag)) from 5.5 to 25 h. In this study, NaCl, pH and phenol conditions were similar to those currently observed in smoked salmon production. This shows that L. monocytogenes ScottA growth could be efficiently delayed by the use of div41 in addition to the usual technological hurdles. In conclusion, the technological hurdles of cold smoked salmon production could be further optimized and combined with the use of div41 or the div41 producer strain to improve the food safety of the product.

Control of biological hazards in cold smoked salmon production

An outline of the common processing technology for cold smoked salmon in Denmark is presented. The safety hazards related to pathogenic bacteria, parasites and biogenic amines are discussed with special emphasis on hazards related to Clostridium botulinum and Listeria monocytogenes. Critical control points are identified for all hazards except growth of L. monocytogenes. For this reason a limitation of shelf life to three weeks at + 5 °C for cold smoked vacuum-packed salmon having ≥3% water phase salt is recommended.