Inactivation of Listeria monocytogenes in raw and hot smoked trout fillets by high hydrostatic pressure processing combined with liquid smoke and freezing

High hydrostatic pressure (HHP; 200 MPa for 15 min), liquid smoke (0.50%, v/v) and freezing (−80 °C, overnight) was used to eliminate Listeria monocytogenes in BHI broth, raw and smoked trout. The bactericidal effect of liquid smoke solutions (L9 and G6), HHP and their combinations was evaluated against L. monocytogenes LO28, EGD-e and 10403S and further continued with the most resistant strain (10403S) to the combined treatment. For first time, a synergistic effect of liquid smoke and HHP was observed and was further enhanced by freezing prior to HHP. The effect of HHP and liquid smoke, prior to freezing was highest in BHI compared to raw and smoked trout. A major synergistic effect of HHP, liquid smoke and freezing was observed, reaching a 5.48 or 1.93 log CFU/g reduction when smoked or raw trout was used respectively. Furthermore, high injury levels occurred, among treatments reaching up to 55.98%

Non-thermal methods for ensuring the microbiological quality and safety of seafood

A literature search and systematic review were conducted to present and discuss the most recent research studies for the past twenty years on the application of non-thermal methods for ensuring the microbiological safety and quality of fish and seafood. This review presents the principles and reveals the potential benefits of high hydrostatic pressure processing (HHP), ultrasounds (US), non-thermal atmospheric plasma (NTAP), pulsed electric fields (PEF), and electrolyzed water (EW) as alternative methods to conventional heat treatments. Some of these methods have already been adopted by the seafood industry, while others show promising results in inactivating microbial contaminants or spoilage bacteria from solid or liquid seafood products without affecting the biochemical or sensory quality. The main applications and mechanisms of action for each emerging technology are being discussed. Each of these technologies has a specific mode of microbial inactivation and a specific range of use. Thus, their knowledge is important to design a practical application plan focusing on producing safer, qualitative seafood products with added value following today’s consumers’ needs. © 2021 by the authors

Specific Spoilage Organisms (SSOs) in Fish

Fresh and minimally processed fish and seafood spoil due to the action of a consortium of microorganisms, the so-called specific spoilage organisms (SSOs) that have the ability to dominate and produce metabolites that directly affect the sensory properties of the product, resulting in its rejection by the consumers. The selection of SSOs is affected by fish origination, processing, and storage conditions and various implicit factors such as antagonism for nutrients and microbial interactions. The metabolic products of SSOs causing the spoilage are various volatile compounds that mainly come from the assimilation of nonprotein-nitrogen of fish flesh. Qualitative and quantitative determination of SSOs is of great interest, and current molecular techniques provide us with powerful tools for exploring the diversity and dynamics of SSOs. The inhibition of SSOs by applying appropriate preservation strategies can retain fish freshness and extend shelf life. Elucidation of SSOs' metabolic potential and activity and the estimation of the growth and population level provide us with tools for rapid evaluation of fish freshness/spoilage status and remaining shelf life. © 2017 Elsevier Ltd. All rights reserved

Monitoring of spoilage and determination of microbial communities based on 16S rRNA gene sequence analysis of whole sea bream stored at various temperatures

Exploration of initial and spoilage microbiota grown on plates of whole sea bream stored aerobically at 0 (ice), 5 and 15 °C, was conducted by 16S rRNA gene sequence analysis. The course of spoilage was recorded by monitoring microbiological, sensory and chemical changes. Shelf-life of sea bream determined by sensory assessment was 16, 5 and 2 days at 0 (ice), 5 and 15οC, respectively. Pseudomonas spp. was the dominant spoilage population of whole sea bream at all temperatures tested. A sum of 144 colonies were isolated from TSA (Tryptone Soy Agar) plates and identified by genotypic approach at the beginning and at the sensory rejection time points. Regarding initial microbiota, Pseudomonas fragi was the most abundant compared to the rest bacteria (Pseudomonas fluorescens, Enterobacter hormaechei, Chryseobacterium carnipullorum). P. fragi was also the dominant microorganism of fish stored at 0 and 5, while P. fluorescens at 15 οC. Concluding, genotypic approach gives accurate identification of the dominant spoilage microorganisms providing us with valuable information regarding microbiological spoilage of fish. © 2015 Elsevier Ltd

The evolution of knowledge on seafood spoilage microbiota from the 20th to the 21st century: Have we finished or just begun?

Backround: The modern dietary trends have led to a continuously increasing demand for seafood. Both high quality and extended shelf-life of seafood is required to satisfy the nowadays dietary tendency, as well as the industrial interest to increase the added value of such products. However, microbial spoilage is the main factor linked with the rapid seafood sensorial degradation, resulting in high food losses along the production and distribution chain and thus, noteworthy economic losses for seafood producingcountries. In the past, the low technological capability permitted a limited and non-representative study of microbial community and thus, the results of spoilage-related microbiota present in seafood, were led to both insufficient and disputed conclusions. Scope and approach: The scope of the present review is to evaluate how method development has improved our understanding on seafood spoilage microbiota during the past decades, discussing in parallel the current/emerging trends, as well as what could be recommended for future research efforts. Key findings and conclusions: The advent of novel molecular technologies, mainly high throughput sequencing (HTS) set of techniques, has changed our approach regarding the study of seafood microbiota, enriching our knowledge in this field. For improving and/or ensuring seafood quality along seafood value chain, the scientific community has now the option of using such modern tools to explore and understand the complex plenomena taking place during seafood spoilage.The study of seafood microbiota changes during processing, storage and distribution, in combination with the “meta-omics” approaches, is the key to unveil the functionalities in such complicated food matrix. In the current decade, the scientific community faces the challenge to establish novel and intelligent strategies that could prevent seafood spoilage as well as to extend or even predict the shelf-life of seafood. The contribution of multi-omics is expected to enhance this attempt. Those strategies will lead to the production of high quality added value seafood, in order to meet consumers’ demands. © 2022 Elsevier Lt

High pressure processing at ultra-low temperatures: Inactivation of foodborne bacterial pathogens and quality changes in frozen fish fillets

High pressure processing (HPP) at ultra-low temperatures was conducted against Listeria monocytogenes and Salmonella enterica in frozen pink salmon fillets. Quality changes, such as drip loss, color and odor attributes were recorded in non-inoculated pollock, pink salmon and tuna fillets. Pressures at 250 and 400 MPa were applied from 0.5 to 10 min. Reductions up to 3.5 log cfu/g were recorded for the treatments performed at −32 °C, in contrast to −50 °C where the reductions were only up to 1.5 log cfu/g. Higher pressure did not cause higher reduction. It was apparent that the main factor contributing to the bacterial inactivation is the phase transition of ice structure from I to III, in contrast to transition from I to II. Drip loss was not higher than the expected with HPP at temperatures above 0 °C, while color changes were negligible. Finally, the odor evaluation did not exhibit considerable differences between untreated and treated samples. Industrial relevance: High pressure processing at ultra-low temperatures is a promising treatment for bacterial inactivation and retention of quality attributes of frozen fish. Treatment at 250 MPa for only 3 min at temperatures just below −22 °C, which is feasible and affordable, caused a more than 3-log reduction against Listeria monocytogenes and Salmonella enterica, without affecting considerably the quality properties. Thus, the application of low pressure and shorter processing times gives a great potential for industrial application for frozen fish or fish that wouldn't be undesirable to freeze before pressurization. © 2021 Elsevier Lt

Pathogens and their sources in freshwater fish, sea finfish, shellfish, and algae

Fish production is one of the most important solutions to tackle the great challenges of the 21st century, such as how to feed people in the context of a growing population. However, pathogens such as bacteria, including antimicrobial-resistant populations and viruses, can be present in the water column and fish (also including shellfish) threatening food security and public health. Pathogens can be transferred from human settlements, cropping systems, livestock systems, animal slaughtering and processing industries, and from other sources of human and animal activity, into the aquatic environment and contaminate fish. Fish contamination can be also continued in harvesting, handling, packaging, processing, and distribution, because of poor hygiene or sanitary practices in the post-farm gate. Such pathogens can end up in humans through the food value chain and fall ill after eating contaminated fish. Several pathogenic strains, serotypes or serovars of Vibrio vulnificus, Vibrio parahaemolyticus, Vibrio cholerae, Salmonella enterica, Aeromonas sp., Listeria monocytogenes, and Clostridium botulinum are responsible for thousands of cases and deaths associated with fish consumption around the globe. Of them, Vibrio, Salmonella, Aeromonas, and L. monocytogenes isolated from farmed fish, have been found to present antibiotic resistance to various antimicrobial agents. Researchers can now detect such pathogenic bacteria using cutting-edge methodologies for example, conventional PCR, Real-Time PCR, High-Resolution Melting, and technologies such as Next Generation Sequencing. Such innovations have immensely contributed to our understanding of how to solve problems of stakeholders related to seafood safety, minimize hazard related issues, and tackle food and economic losses in pre- and post- fish farm gate, thereby providing products of the highest safety in the world. © 2023 International Life Sciences Institute (ILSI) Published by Elsevier Inc. All rights reserved

Dynamics of biofilm formation by Listeria monocytogenes on stainless steel under mono-species and mixed-culture simulated fish processing conditions and chemical disinfection challenges

The progressive ability of a six-strains L. monocytogenes cocktail to form biofilm on stainless steel (SS), under fish-processing simulated conditions, was investigated, together with the biocide tolerance of the developed sessile communities. To do this, the pathogenic bacteria were left to form biofilms on SS coupons incubated at 15 °C, for up to 240 h, in periodically renewable model fish juice substrate, prepared by aquatic extraction of sea bream flesh, under both mono-species and mixed-culture conditions. In the latter case, L. monocytogenes cells were left to produce biofilms together with either a five-strains cocktail of four Pseudomonas species (fragi, savastanoi, putida and fluorescens), or whole fish indigenous microflora. The biofilm populations of L. monocytogenes, Pseudomonas spp., Enterobacteriaceae, H2S producing and aerobic plate count (APC) bacteria, both before and after disinfection, were enumerated by selective agar plating, following their removal from surfaces through bead vortexing. Scanning electron microscopy was also applied to monitor biofilm formation dynamics and anti-biofilm biocidal actions. Results revealed the clear dominance of Pseudomonas spp. bacteria in all the mixed-culture sessile communities throughout the whole incubation period, with the in parallel sole presence of L. monocytogenes cells to further increase (ca. 10-fold) their sessile growth. With respect to L. monocytogenes and under mono-species conditions, its maximum biofilm population (ca. 6 log CFU/cm2) was reached at 192 h of incubation, whereas when solely Pseudomonas spp. cells were also present, its biofilm formation was either slightly hindered or favored, depending on the incubation day. However, when all the fish indigenous microflora was present, biofilm formation by the pathogen was greatly hampered and never exceeded 3 log CFU/cm2, while under the same conditions, APC biofilm counts had already surpassed 7 log CFU/cm2 by the end of the first 96 h of incubation. All here tested disinfection treatments, composed of two common food industry biocides gradually applied for 15 to 30 min, were insufficient against L. monocytogenes mono-species biofilm communities, with the resistance of the latter to significantly increase from the 3rd to 7th day of incubation. However, all these treatments resulted in no detectable L. monocytogenes cells upon their application against the mixed-culture sessile communities also containing the fish indigenous microflora, something probably associated with the low attached population level of these pathogenic cells before disinfection (< 102 CFU/cm2) under such mixed-culture conditions. Taken together, all these results expand our knowledge on both the population dynamics and resistance of L. monocytogenes biofilm cells under conditions resembling those encountered within the seafood industry and should be considered upon designing and applying effective anti-biofilm strategies. © 2017 Elsevier B.V

Volatile organic compounds of microbial and non-microbial origin produced on model fish substrate un-inoculated and inoculated with gilt-head sea bream spoilage bacteria

Volatile organic compounds (VOCs) origination during fish spoilage is attributed to either decomposition of fish constituents or metabolic activity of spoilage bacteria. To identify microbiological spoilage markers it is essential to know which VOCs are microbial metabolites. VOCs produced in sterile fish juice agar (FJA) model substrate made from gilt-head sea bream (Sparus aurata) flesh juice, inoculated or not with spoilage bacteria isolated from sea bream fillets were detected using SPME/GC-MS technique. Three groups of spoilage bacteria (Pseudomonas, Shewanella and Carnobacterium/Lactobacillus strains) were used to inoculate Petridishes with FJA and stored at 0 and 15 °C under air and commercial Modified Atmosphere Package (MAP CO2: 60%, O2: 10%, N2: 30%). Bacterial growth was also monitored. VOCs that were detected in sterile substrate and their amounts were not higher in inoculated FJA were presumably of non-microbial origin. VOCs that were detected only in inoculated FJA were metabolic products of spoilage bacteria. Some of VOCs were associated with metabolic activity of a particular microbial group, e.g. ethyl esters were associated with Pseudomonas, while 2-, 3-methylbutanal and 3-hydroxy-2-butanone with LAB. Few microbial metabolites increased during storage showing their potential as spoilage markers of gilt-head sea bream and the possible use for rapid freshness assessment. © 2016 Elsevier Lt