A comparative study of Atlantic salmon chilled in refrigerated seawater versus on ice: from whole fish to cold-smoked fillets

Insight to the diversity of Photobacterium spp. isolated from European plaice (Pleuronectes platessa) based on phylogenetic analysis, phenotypic characterisation and spoilage potential

This study aimed to explore the diversity of fifty-four Photobacterium strains isolated from muscle tissue of European plaice (Pleuronectes platessa) caught at different fishing seasons and stored 14-days under various conditions. Single phylogenetic markers (16S rRNA, gapA, gyrB and recA) and multilocus sequence analysis (MLSA) were employed to classify isolates at species level. Furthermore, intra- and interspecies variability in the phenotypic traits, maximum specific growth rate (μmax) and spoilage potential of the Photobacterium isolates were investigated. The isolates were classified into the P. iliopiscarium (53.7 %), P. phosphoreum (40.7 %) and P. piscicola (5.6 %) clades using MLSA. Two housekeeping genes, gyrB and recA, exhibited a consistent phylogenetic relationship with MLSA, suggesting that they might be used as individual phylogenetic markers for the Photobacterium genus. Intra- and interspecies variability in the expression of phenotypic characteristics and the production of trimethylamine (TMA), inosine (HxR), and hypoxanthine (Hx) were observed. A growth optimum temperature for P. iliopiscarium was approximately 20 °C, while those for P. phosphoreum and P. piscicola were closer to 15 °C. All isolates exhibited the highest growth density at 1.5 % NaCl, followed by 0.5 %, 3 %, and 6 % NaCl. However, P. phosphoreum demonstrated a higher NaCl tolerance than the other two species. Although, the high CO2 atmosphere significantly inhibited the growth of all strains at 4 °C, P. phosphoreum and P. piscicola showed higher growth density at 15 °C than P. iliopiscarium. Notably, all strains demonstrated H2S production. The μmax varied considerably within each species, highlighting the significance of strain-level variability. This study demonstrates that P. iliopiscarium and P. piscicola, alongside P. phosphoreum, are efficient TMA-, HxR-, Hx-, and H2S-producers, suggesting their potential contribution to synergistic off-odour generation and spoilage. Moreover, the Photobacterium isolates seem to exhibit diverse adaptations to their environments, resulting in fluctuated growth and spoilage potential. Understanding intra- and interspecies variability will facilitate modelling seafood spoilage in microbial risk assessments and developing targeted hurdles to prolong products' shelf-life.

Extending the Shelf Life of Atlantic Salmon (Salmo salar) with Sub-Chilled Storage and Modified Atmosphere Packaging in Recyclable Mono-Material Trays

This study investigated the effect of sub-chilling whole gutted salmon and sub-chilled storage at -1 °C in modified-atmosphere packaging in two recyclable mono-material trays (CPET, HDPE). Quality parameters were measured, including water-holding properties, salt content, color, texture, lipid oxidation, and sensory and microbiological shelf life. The oxygen transmission rate was measured for the packages. Compared to traditional fish storage on ice, sub-chilling gave a 0.4% weight gain, better water-holding capacity, and higher salt content. The sub-chilled fish gave a significantly better sensory quality and microbiological shelf life of up to 49 days. Photobacterium was the dominating bacteria during storage. Salmon packaged in CPET trays had a higher drip loss than HDPE trays, but a lower rate of lipid oxidation (1-penten-3-ol). Our results showed the feasibility of significantly extending shelf life with sub-chilling, removing the need for ice. Moreover, using recyclable trays for packaging contributes to a circular economy without compromising food quality.

Effects of capture-related stress and pre-freezing holding in refrigerated sea water (RSW) on the muscle quality and storage stability of Atlantic mackerel (Scomber scombrus) during subsequent frozen storage

Crowded (stressed) and unstressed Atlantic mackerel with or without pre-freezing holding in refrigerated sea water (RSW) were stored at -19 °C for ∼12 months and analysed for nucleotide degradation (K value), muscle pH, water holding capacity (WHC), fillet firmness, cathepsin B/L like activity, lipid oxidation and fillet colour. The frozen storage showed the largest and most consistent direct effects on the quality metrics leading to increased lipid oxidation, discolouration (yellowing) and reduction on WHC and cathepsin activity. RSW treatment promoted nucleotide degradation and reduced WHC and fillet firmness in interaction with frozen storage and affected fillet colour lightness and saturation. Although showing only marginal main effects, crowding stress modified WHC, cathepsin activity and fillet firmness and colour through significant interactions with the frozen storage and RSW treatment. Further studies with larger sample sizes would be needed to elucidate their complex effects and interactions on the quality and storage stability of mackerel.

Effect of Nanoemulsion Containing Enterocin GR17 and Cinnamaldehyde on Microbiological, Physicochemical and Sensory Properties and Shelf Life of Liquid-Smoked Salmon Fillets

The spoilage of liquid-smoked salmon represented a serious restriction for shelf life, due to the loss of taste, smell, color and consistency in product quality. The objective of this study was to investigate the feasibility of applying a nanoemulsion delivery system co-encapsulated enterocin Gr17 and essential oils (EOs) to the refrigerated storage of liquid-smoked salmon. The synergistic inhibiting effects of enterocin Gr17 and EOs were evaluated, a nanoemulsion delivery system with the optimal combination was developed, and the evolution of the microbiological, physicochemical, and sensory properties of liquid-smoked salmon fillets were analyzed during a 49-day period of refrigerated storage. The results showed that the combination of enterocin Gr17 and cinnamaldehyde essential oil (CEO) displayed the strongest synergistic inhibiting effect on foodborne pathogens. A nanoemulsion system incorporating enterocin Gr17 and CEO was successfully developed and presented a broad spectrum of activity against most of the tested bacteria. A nanoemulsion system incorporating enterocin Gr17 and CEO (CO-NE) could significantly inhibit the growth of microflora, suppress the accumulation of total volatile basic nitrogen (TVB-N) and thiobarbituric acid reactive substance (TBARS), and maintain better color, texture, and sensory profiles during smoked salmon storage at 4 °C. Overall, from a microbiological, physicochemical, and sensory point of view, the CO-NE treatment could extend the shelf life to 42 days and maintain the relatively low TVB-N value (≤15.38 mg/100 g), TBARS value (≤2.51 mg MDA/kg), as well as a relatively high sensory score (≥5.83) during the whole storage period. Hence, a nanoemulsion system incorporating enterocin Gr17 and CEO could be a promising bio-preservative technology and alternative to the conventional processes used for improving the safety and quality of chilled liquid-smoked salmon.

Assessment of the Effects of Salt and Salicornia herbacea L. on Physiochemical, Nutritional, and Quality Parameters for Extending the Shelf-Life of Semi-Dried Mullets (Chelon haematocheilus)

Mullet, a coastal fish species, is commonly used as a salted dried fish in many countries, including Korea, Japan, and the southeastern United States. The purpose of this investigation was to develop high-quality products of salted semi-dried mullet (SSDM) using natural salt and Salicornia herbacea L. (SAL). The antioxidant activity of SAL was investigated by in vitro studies. The physicochemical and nutritional characteristics of fresh mullet (FM), salted control (SSDM-CON), and SAL-treated (SSDM-SAL) mullet groups were analyzed. The moisture, ash, and crude protein contents were significantly increased in the SSDM-SAL group, whereas the salinity was decreased when compared with the SSDM-CON group. Lipid oxidation occurred in the FM and SSDM groups, as indicated by the increase in peroxide (PV), acid (AV), and thiobarbituric acid reactive substance (TBARS) values during the storage period. The protein pattern on the sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis showed similarities between the groups, while the amino acid and fatty acid contents also varied in the FM and SSDM groups depending on their processing methods. Initially, the total bacterial count was significantly higher in the SSDM groups than in the FM group. However, the SSDM-SAL group had a markedly lower total bacteria count than the FM and SSDM-CON groups during 21 days of refrigerated storage. This result indicates that SAL treatment can improve mullet’s safety from microorganisms, includes beneficial biochemical parameters, and can extend their shelf-life through refrigerated storage.

Water holding properties of Atlantic salmon

With global seafood production increasing to feed the rising population, there is a need to produce fish and fishery products of high quality and freshness. Water holding properties, including drip loss (DL) and water holding capacity (WHC), are important parameters in determining fish quality as they affect functional properties of muscles such as juiciness and texture. This review focuses on the water holding properties of Atlantic salmon and evaluates the methods used to measure them. The pre- and postmortem factors and how processing and preservation methods influence water holding properties and their correlations to other quality parameters are reviewed. In addition, the possibility of using modelling is explained. Several methods are available to measure WHC. The most prevalent method is the centrifugation method, but other non-invasive and cost-effective approaches are increasingly preferred. The advantages and disadvantages of these methods and future trends are evaluated. Due to the diversity of methods, results from previous research are relative and cannot be directly compared unless the same method is used with the same conditions.

Effect of Cold Smoking and Natural Antioxidants on Quality Traits, Safety and Shelf Life of Farmed Meagre (Argyrosomus regius) Fillets, as a Strategy to Diversify Aquaculture Products

Aquaculture has been playing a leading role over the years to satisfy the global growing demand for seafood. Moreover, innovative techniques are necessary to increase the competitiveness, sustainability and profitability of the seafood production chain, exploiting new species from the aquaculture, such as meagre (Argyrosomus regius), to develop value-added products and diversify their production. In the present work, the effectiveness of cold smoking combined with antioxidants (SA) compared to cold smoking alone (S) on meagre fillets, the quality and shelf life were investigated. Sensory, biochemical, physical–chemical and microbiological analyses were performed on the smoked fillets during vacuum-packaged storage for 35 days at 4 ± 0.5 °C. The results showed positive effects of the SA treatment on the biochemical parameters of meagre fillets. The total volatile basic nitrogen (TVB-N) in smoked meagre fillets was significantly lower in the SA treatment at the end of storage compared to the S treatment. Moreover, SA had a positive effect on lipid peroxidation. Lower values of malondialdehyde (mg MDA/kg) were observed in the SA treatment during preservation compared to the S treatment. This work will contribute to the growth of the fish production chain, producing a value-added fish product by exploiting meagre, whose production has been increasing over decades.