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

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%. Industrial relevance: This paper illustrates for first time, the possibility of using a very low pressure in combination with liquid smoke and freezing to eliminate L. monocytogenes. It was demonstrated that treatment of trout samples with liquid smoke followed by freezing prior to pressurization at 200 MPa for 15 min reduced the number of L. monocytogenes by more than 5-log CFU/g. Such a remarkable bacterial inactivation at a very low pressure (compared to common industrial practices) is a significant achievement that could allow production of safer and novel products by HHP at an affordable price, as the cost of equipment manufacture as well as the maintenance and running costs could be reduced substantially at lower operation pressures

Microbiological spoilage and investigation of volatile profile during storage of sea bream fillets under various conditions

Volatile organic compound (VOC) profile was determined during storage of sea bream (Sparus aurata) fillets under air and Modified Atmosphere Packaging (MAP CO2/O-2/N-2: 60/10/30) at 0,5 and 15 degrees C. Microbiological, TVB-N (Total Volatile Base Nitrogen) and sensory changes were also monitored. Shelf-life of sea bream fillets stored under air was 14,5 and 2 days (d) at 0,5 and 15 degrees C respectively, while under MAP was 18, 8, and 2 d at 0, 5 and 15 degrees C respectively. At the end of shelf life, the total microbial population ranged from 7.5 to 8.5 log cfu/g. Pseudomonas spp. were among the dominant spoilage microorganisms in all cases, however growth of Brochothrix thermosphacta and Lactic Acid Bacteria (LAB) were favoured under MAP compared to air. TVB-N production was favoured at higher temperatures and under air compared to lower temperatures and MAP. TVB-N increased substantially from the middle of storage and its value never reached concentrations higher than 30-35 mg N/100 g, which is the legislation limit, making it a poor chemical spoilage index (CSI). A lot of alcohols, aldehydes, ketones and ethyl esters that were detected in the present study have been reported as bacterial metabolites, others as products of chemical oxidation while others as aroma constituents. VOCs such as 3-methylbutanal, acetic acid, ethanol, ethyl esters of isovaleric and 2-methylbutyric acids, 1-penten-3-ol, 1-octen-3-ol and cis-4-heptenal appeared from the early or middle stages and increased until the end of storage. From those only 3-methylbutanal, acetic add, ethanol and the ethyl esters have been reported as microbial origin, making them potential CSI candidates of sea bream fillets. (C) 2014 Elsevier B.V. All rights reserved

Indigenous and spoilage microbiota of farmed sea bream stored in ice identified by phenotypic and 16S rRNA gene analysis

Investigation of the initial and spoilage microbial diversity of iced stored sea bream was carried out. Culture dependent methods were used for bacterial enumeration and phenotypic identification of bacterial isolates, while culture independent methods, using bacterial 16S rRNA gene amplification, cloning and sequencing of DNA extracted directly from the flesh were also employed. The culture dependent approach revealed that the initial microbiota was dominated by Acinetobacter, Shewanella, Pseudomonas and Flavobacterium, while at the end of shelf-life determined by sensory analysis (16 days), the predominant microbiota was Pseudomonas and Shewanella. Culture independent approach showed that initially the sea bream flesh was strongly dominated by Acinetobacter, while Pseudomonas, Aeromonas salmonicida and Shewanella were the predominant phylotypes at the end of shelf-life. Initial and spoilage microbiota comprised of phylotypes previously identified by others using traditional or molecular techniques. However, Aeromonas has not been reported as part of the dominant microbiota of sea bream at the time of spoilage. Combination of classical and molecular methodologies better reveals the microbiota during storage by revealing bacteria that escape standard approaches and, thus, provides valuable complementary information regarding microbiological spoilage. © 2012 Elsevier Ltd

Effect of Satureja thymbra Essential Oil on Growth-No Growth Interfaces of Listeria monocytogenes Scott A and Salmonella Enteritidis PT4, at Various Temperatures, pH, and Water Activities

Antimicrobial efficacy of Satureja thymbra essential oil against Listeria monocyto genes Scott A and Salmonella ser. Enteritidis PT4 was evaluated in vitro by modeling the growth boundaries at various temperatures, pH, and NaCl concentrations. Growth no growth (turbidity) data were modeled by logistic polynomial regression. The concordance indices and the Hosmer- Lemeshow statistics of both logistic models indicated a good fit to the observed data. Salmonella Enteritidis was more sensitive at increasing salt content as compared with L. monocytogenes. On the other hand, pH changes had greater effect on growth initiation of L. monocytogenes than they had on growth initiation of Salmonella Enteritidis. Presence of essential oil up to 0.06% (vol/vol) had no or little effect on growth initiation of both microorganisms tested, while the concentration of 0.1% (vol/vol) essential oil exhibited great inhibition on growth initiation, especially when it was combined with increased salt content and low temperatures. The antimicrobial potency of S. thymbra essential oil was more pronounced when multiple hurdles were applied. Modeling the growth boundaries offers a useful tool to food microbiologists for assessing the antimicrobial activity in a range of food preservation conditions as compared with the conventional MIC determination

Preservation status and microbial communities of vacuum-packed hot smoked rainbow trout fillets

Vacuum-packed hot smoked rainbow trout fillets from two different smokehouses of Greece were stored at 2 and 7.9 °C. Microbiological, sensory, and physicochemical changes were monitored. Microbial communities grown on MRS of three different pHs (5.4, 6.4 and 7.4) were also classified and identified using Matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS). Shelf-life was found to differ between products from the two smokehouses (A: 104 and 45 days, B: 100 and 45 days, at 2 and 7.9 °C, respectively). At the time point that sensory rejection was recorded, counts on MRS were found at higher population levels than the other microorganisms tested, almost in all cases. Out of the 567 colonies isolated from MRS of three different pHs, 71 classified as Enterococcus spp., 383 as Candida spp. and 113 as Lactobacillus spp. Candida zeylanoides dominated exclusively in fillets from the smokehouse A during storage at 2 °C, while Lactobacillus sakei dominated clearly against C. zeylanoides at 7.9 °C, in all pH values. For the smokehouse B, C. zeylanoides or Enterococcus faecalis found to dominate initially in MRS of three pHs, C. zeylanoides, and/or Candida famata in the middle and/or the time point that sensory rejection was recorded at 2 °C, while Lactobacillus curvatus or E. faecalis at 7.9 °C. This study reveals the predominant cultivable spoilage microbiota of vacuum-packed hot smoked rainbow trout, and provides valuable information to the researcher and producers towards the production of more stable products with improved shelf-life

Volatilome of Chill-Stored European Seabass (Dicentrarchus labrax) Fillets and Atlantic Salmon (Salmo salar) Slices under Modified Atmosphere Packaging

Fish spoilage occurs due to production of metabolites during storage, from bacterial action and chemical reactions, which leads to sensory rejection. Investigating the volatilome profile can reveal the potential spoilage markers. The evolution of volatile organic molecules during storage of European seabass (Dicentrarchus labrax) fillets and Atlantic salmon (Salmo salar) slices under modified atmosphere packaging at 2 ◦C was recorded by solid-phase microextraction combined with gas chromatography-mass spectrometry. Total volatile basic nitrogen (TVB-N), microbiological, and sensory changes were also monitored. The shelf life of seabass fillets and salmon slices was 10.5 days. Pseudomonas and H2S-producing bacteria were the dominant microorganisms in both fish. TVB-N increased from the middle of storage, but never reached concentrations higher than the regulatory limit of 30–35 mg N/100 g. The volatilome consisted of a number of aldehydes, ketones, alcohols and esters, common to both fish species. However, different evolution patterns were observed, indicating the effect of fish substrate on microbial growth and eventually the generation of volatiles. The compounds 3-hydroxy-2-butanone, 2,3-butanediol, 2,3-butanedione and acetic acid could be proposed as potential spoilage markers. The identification and quantification of the volatilities of specific fish species via the development of a database with the fingerprint of fish species stored under certain storage conditions can help towards rapid spoilage assessment. © 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/)

Bacterial Communities and Antibiotic Resistance of Potential Pathogens Involved in Food Safety and Public Health in Fish and Water of Lake Karla, Thessaly, Greece

Bacterial communities, microbial populations, and antibiotic resistance of potential pathogens in the water and fish (Cyprinus carpio, flesh and gut) from different areas (A1, A2 and A3—A1 was linked with river water, A2 with cattle activity, and A3 with waters of a spring after heavy rains) of Lake Karla (Thessaly, Central Greece) were investigated. The isolated bacteria were identified using Matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS) and were tested for resistance in 21 antibiotics. The microbiota composition of fish flesh was also studied using 16S amplicon-based sequencing Serratia fonticola and several species of Aeromonas (e.g., Aeromonas salmonicida, Aeromonas bestiarium, Aeromonas veronii, etc.) exhibited the highest abundances in all studied samples, while the microbiota profile between the three studied areas was similar, according to the culture-dependent analysis. Of them, S. fonticola was found to be resistant in the majority of the antibiotics for the water and fish (gut and flesh), mainly of the areas A1 and A2. Regarding 16S metabarcoding, the presence of Serratia and Aeromonas at genus level was confirmed, but they found at very lower abundances than those reported using the culture-dependent analysis. Finally, the TVC and the rest of the studied microbiological parameters were found at acceptable levels (4 log cfu/mL or cfu/g and 2–4 log cfu/mL or cfu/g, extremely low levels of E. coli/coliforms) in both water and fish flesh. Based on our findings, the water of Lake Karla would be used for activities such as irrigation, recreation and fishing, however, the development and implementation of a quality management tool for Lake Karla, to ensure environmental hygiene and prevention of zoonosis during the whole year, is imperative. © 2022 by the authors

Microbiota and volatilome profile of fresh and chill-stored deepwater rose shrimp (Parapenaeus longirostris)

Bacterial communities and Volatile Organic Compounds (VOCs) profile of deepwater rose shrimp (Parapenaeus longirostris) stored at 0 °C (ice) and 4 °C were investigated using 16S amplicon based sequencing and Solid phase micro-extraction (SPME) - Gas chromatography/mass spectrometry (GC/MS), respectively. The shelf-life of shrimps determined by sensory assessment was 5 and 2 days at 0 °C and 4 °C, respectively. Based on 16S analysis (culture-independed), the initial microbiota of shrimps mainly consists of Photobacterium, Candidatus Hepatoplasma, Psychrobacter, Acinetobacter and Delftia. Psychrobacter and Carnobacterium dominated during storage at both temperatures. Psychrobacter was the most dominant taxon at the end of shelf-life of chill-stored shrimps. A minor microbial population composed by Brevundimonas, Stenotrophomonas, Staphylococcus, Legionella, Acinetobacter, Bacillus, Escherichia-Shigella, Enterococcus, Enterobacter, Klebsiella was also detected. Those taxa may be originated from the environment due to an inadequate hygienic practice during fishing, handling and icing. VOCs such as ethanol, 3-methyl-1-butanol, 2-ethyl-1-hexanol, 3-hydroxy-2-butanone, indole etc., were found to be associated with shrimps at 4 °C, while acetone and dimethyl sulfide with shrimps in ice. Some VOCs, from microbial or chemical origin, increased in shrimps either at 0 °C (i.e. 1-octen-3-ol, trans-2-octenal) or at 4 °C (i.e. 3-methyl-1-butanol, indole), while 2-methylbutanal and 3-methylbutanal increased in both temperatures. A positive correlation between Psychrobacter with 2-ethyl-1-hexanol and Carnobacterium with 3-methyl-1-butanol was also observed. Concluding, we suggest the reinforcement of Good Hygiene Practices on fishing boats during fishing/handling, the rapid onboard icing and keeping shrimps iced avoiding even small increase of storage temperature that affects quality parameters (e.g. microbial population level, synthesis of microbiota, VOCs profile) in order to provide a product of the highest quality and safety in the market. © 2020 Elsevier Lt