Seafood Spoilage Research Articles

Adaptation of the Marine Bacterium Shewanella baltica to Low Temperature Stress.

Marine bacteria display significant versatility in adaptation to variations in the environment and stress conditions, including temperature shifts. Shewanella baltica plays a major role in denitrification and bioremediation in the marine environment, but is also identified to be responsible for spoilage of ice-stored seafood. We aimed to characterize transcriptional response of S. baltica to cold stress in order to achieve a better insight into mechanisms governing its adaptation. We exposed bacterial cells to 8 °C for 90 and 180 min, and assessed changes in the bacterial transcriptome with RNA sequencing validated with the RT-qPCR method. We found that S. baltica general response to cold stress is associated with massive downregulation of gene expression, which covered about 70% of differentially expressed genes. Enrichment analysis revealed upregulation of only few pathways, including aminoacyl-tRNA biosynthesis, sulfur metabolism and the flagellar assembly process. Downregulation was observed for fatty acid degradation, amino acid metabolism and a bacterial secretion system. We found that the entire type II secretion system was transcriptionally shut down at low temperatures. We also observed transcriptional reprogramming through the induction of RpoE and repression of RpoD sigma factors to mediate the cold stress response. Our study revealed how diverse and complex the cold stress response in S. baltica is.

Comparative Proteome Analysis of Shewanella putrefaciens WS13 Mature Biofilm Under Cold Stress.

Worldwide, Shewanella putrefaciens is the predominant seafood spoilage microorganism during cold storage. This bacterium can attach to biotic/abiotic surfaces to form biofilms which contribute to seafood quality degradation and shelf-life reduction. The mechanism of S. putrefaciens biofilm formation is not yet described. Crystal violet staining in combination with confocal laser scanning microscopy (CLSM) was used to study the sequence of events leading to the establishment of a mature biofilm at 4, 15, and 30°C. In addition, the main chemical constituents of the mature biofilm were determined by Raman spectroscopy (RM), whereas, comparative proteomic analysis was used to quantify changes in metabolic pathways and to find out underlying protein determinants. The physical dimensions of the mature biofilm, i.e., biomass, biovolume, and mean thickness, were higher at 4°C when compared to 15 and 30°C. The variations of proteins measured by RM confirmed the importance of proteins during the formation of a mature biofilm. Comparative proteomic analysis showed that siderophore and iron chelate transport proteins were down-regulated during mature biofilm formation. The down-regulated aforementioned proteins are involved in promoting iron storage in response to a higher demand for metabolic energy, whereas, the upregulated proteins of the sulfur relay system, pyrimidine metabolism, and purine metabolism are related to bacterial adaptability. Synthesis of proteins related to cold stress was increased and proteins involved in aminoacyl-tRNA biosynthesis were up-regulated, whereas, proteins involved in aminopeptidase activity were down-regulated. Proteolysis to scavenge energy was reduced as proteins involved in pyrophosphatase activity were up-regulated. Also extracellular eDNA was found which may play an important role in maintaining the stability of mature S. putrefaciens biofilm structures under cold stress. This work provides a better understanding of the role of proteins in mature biofilms. In addition, the biofilm formation mechanism of a psychrotrophic spoilage bacterial species at low temperature is explored, which may contribute to generating biofilm controlling strategies during seafood preservation and processing.

Semi-quantitative evaluation of seafood spoilage using filter-paper strips loaded with an aggregation-induced emission luminogen

The method for seafood spoilage detection is far from satisfactory for ensuring food safety and security. Here, we develop a simple and cost-effective method using the filter papers loaded with a dihydroquinoxaline derivative (H + DQ2) to monitor salmon spoilage. The correlation between the content of solid biogenic amines and the photoluminescence intensity (PL) of H + DQ2 induced by amine vapours showed that the PL intensities of H + DQ2 increased with the increase of spoilage, which indicates that it is feasible to evaluate the spoilage degree of salmon based on the PL intensity of H + DQ2-loaded filter papers by semi-quantitation. The optimum detection condition is 75, 50 and 50 g of salmon, 75, 25 and 10 µM H + DQ2 at 0, 4 and 25 °C, respectively. This study provides a quick and simple way for testing amine vapour from fish and provides baseline information for developing an easy-to-use on-site method to evaluate seafood quality for customers.

Transcriptome and Volatilome Analysis During Growth of Brochothrix thermosphacta in Food: Role of Food Substrate and Strain Specificity for the Expression of Spoilage Functions.

Brochothrix thermosphacta is one of the main spoilers in food, responsible for meat and seafood spoilage through the production of malodorous volatile organic compounds. The molecules produced by this bacterium depend on the substrate (meat or seafood) and the storage conditions such as gas mixtures used in the packaging. It seems also that the spoilage potential is strain dependent as production of diacetyl and acetoin, two molecules responsible for seafood spoilage, varies with strains. Therefore, this suggests the involvement of different metabolic functions depending on both food substrate and strain capacities. In this study, we selected two strains with different abilities to produce diacetyl and acetoin and compared their behavior after grown in beef or cooked peeled shrimp juices. We determined the genes upregulated by both strains depending on the growth substrate and those that were specifically upregulated in only one strain. The genes upregulated by both strains in meat or in shrimp juice revealed the importance of the substrate for inducing specific metabolic pathways. The examination of genes that were specifically upregulated in only one of the two strains revealed strain features associated to specific substrates and also strain-specific regulations of metabolic pathways putatively leading to different levels of spoilage molecule production. This shows that the spoilage potential of B. thermosphacta depends on nutrients provided by food substrate and on metabolic activity potential that each strain possesses.

Preparation of an intelligent film based on chitosan/oxidized chitin nanocrystals incorporating black rice bran anthocyanins for seafood spoilage monitoring

A novel intelligent film was developed by immobilizing 1%, 3% and 5% black rice bran anthocyanins (BACNs) into oxidized-chitin nanocrystals (O-ChNCs)/ chitosan (CS) matrix. The ultraviolet-visible spectrum of BACNs solutions showed color variations from red to greyish green in a range of pH 2.0–12.0. Fourier transform infrared spectrum and atomic force microscope of the films showed that O-ChNC and BACNs were well dispersed into the CS matrix. Although the incorporation of BACNs decreased the mechanical and barrier properties of the CS/O-ChNCs/BACNs (COB) films, it endowed the COB films with excellent UV-barrier, antioxidant and pH sensitivity character. The results of the application trial showed that the COB films containing 3% of BACNs (COB-3) were able to monitor the spoiling of fish and shrimp by visible color changes. Therefore, the developed COB-3 films could be used as an intelligent food packaging for monitoring animal-based protein food spoilage.

Systematic analysis of lysine acetylome reveals potential functions of lysine acetylation in Shewanella baltica, the specific spoilage organism of aquatic products

Protein lysine acetylation is a major post-translational modification and plays a critical regulatory role in almost every aspect in both eukaryotes and prokaryotes, yet there have been no data on Shewanella baltica, which is one of the specific spoilage organism (SSO) of aquatic products. Here, we performed the first global acetylproteome analysis of S. baltica. 2929 lysine acetylation sites were identified in 1103 proteins, accounting for 26.1% of the total proteins which participate in a wide variety of biological processes, especially in the constituent of ribosome, the biosynthesis of aminoacyl-tRNA, the amino acids and fatty acid metabolism. Besides, 14 conserved acetylation motifs were detected in S. baltica. Notably, various directly or indirectly spoilage-related proteins were prevalently acetylated, including enzymes involved in the unsaturated fatty acids biosynthesis closely related to the cold adaptability, cold shock proteins, pivotal enzymes involved in the putrescine biosynthesis, and a LuxR-type protein in quorum sensing system. The acetylome analysis in Shewanella can supplement the database and provide new insight into uncovering the spoilage mechanisms of S. baltica. The provided dataset illuminates the potential role of reversible acetylation in S. baltica, and serves as an important resource for exploring the physiological role of lysine acetylation in prokaryotes. SignificanceThe psychrotrophic nature and the ability of S. baltica to make good use of “habitat” nutrients explain its importance in spoilage of seafood stored at low temperatures. However, the underlying mechanism of spoilage potential from the perspective of protein post-translational modification was rarely studied. This work identifies the first comprehensive survey of a lysine acetylome in S. baltica and uncovers the involvement of lysine acetylation in the diverse biological processes, especially in the closely spoilage-related pathways. This study provides a resource for functional analysis of acetylated proteins and creates opportunities for in-depth elucidation of the physiological role of protein acetylation in Shewanella spp.

Spoilage evaluation of raw Atlantic salmon (Salmo salar) stored under modified atmospheres by multivariate statistics and augmented ordinal regression

The development of quality monitoring systems for perishable food products like seafood requires extensive data collection under specified packaging and storage conditions, followed by advanced data analysis and interpretation. Even though the benefits of using volatile organic compounds as food quality indices have been recognized, few studies have focused on real-time quantification of the seafood volatilome and subsequent systematic identification of the most important spoilage indicators. In this study, spoilage of Atlantic salmon (Salmo salar) stored under modified atmospheres (% CO2/O2/N2) and air was characterized by performing multivariate statistical analysis and augmented ordinal regression modelling for data collected by microbiological, chemical and sensory analyses. Out of 25 compounds quantified by selected-ion flow-tube mass spectrometry, ethanol, dimethyl sulfide and hydrogen sulfide were found characteristic under anaerobic conditions (0/0/100 and 60/0/40), whereas spoilage under air was primarily associated with the production of alcohols and ketones. Under high-O2 MAP (60/40/0), only 3-methylbutanal fulfilled the identification criteria. Overall, this manuscript presents a systematic and widely applicable methodology for the identification of most potential seafood spoilage indicators within the context of intelligent packaging technology development. In particular, parallel application of statistics and modelling was found highly beneficial for the performance of the quality characterization process and for the practical applicability of the obtained results in food quality monitoring.

Genotypic and phenotypic characterization of the food spoilage bacterium Brochothrix thermosphacta

Microbial food spoilage is responsible for significant economic losses. Brochothrix thermosphacta is one of the major bacteria involved in the spoilage of meat and seafood. Its growth and metabolic activities during food storage result in the production of metabolites associated with off-odors. In this study, we evaluated the genotypic and phenotypic diversity of this species. A collection of 161 B. thermosphacta strains isolated from different foods, spoiled or not, and from a slaughterhouse environment was constituted from various laboratory collections and completed with new isolates. A PCR test based on the rpoB gene was developed for a fast screening of B. thermosphacta isolates. Strains were typed by MALDI-TOF MS, rep-PCR, and PFGE. Each typing method separated strains into distinct groups, revealing significant intra-species diversity. These classifications did not correlate with the ecological origin of strains. The ability to produce acetoin and diacetyl, two molecules associated with B. thermosphacta spoilage, was evaluated in meat and shrimp juices. The production level was variable between strains and the spoilage ability on meat or shrimp juice did not correlate with the substrate origin of strains. Although the B. thermosphacta species encompasses ubiquitous strains, spoiling ability is both strain- and environment-dependent.

PREVALENCE OF MULTIPLE ANTIBIOTIC RESISTANT AND HAEMOLYSIN PRODUCING BACTERIA IN MARKETED FISH SAMPLES

Sea foods hold one of the greatest potentials to meet current and future demands of proteins to feed the world’s ever-burgeoning population. Fresh seafood is an excellent source of proteins, a good source of minerals, and some vitamins, and it is low in fats, cholesterol, and sodium. Fishery products which are of great importance for human nutrition worldwide and provide clear health benefits. Food borne pathogens are the leading causes of illness and death in less developed countries killing approximately 1.8 million people annually. Bacteria are the most important cause of seafood spoilage. Percentage prevalence of bacterial population in fish samples collected from Ukkadam fish market, Coimbatore was significantly higher during the study period. About 7 fish intestinal samples were then enriched in nutrient broth and cultured. Biochemical test were performed to determine their phenotypic characteristics. The antibiotic resistance pattern and MAR index showed an increased antibiotic resistant bacterium in fish which may severe food borneillness in human. Thehemolytic activity and extracellular protein reveals the frequency of virulence and strong pathogenecity. On this basis, we came to the conclusion that all the isolates are highly pathogenic and cause various food poisoning in humans.

Nanostructured Microcantilevers for the Sensing of Volatile Organic Compounds for Environmental and Food Safety Applications

Biomolecular detection has applications in many fields, including environmental monitoring, food quality monitoring, hazardous gas detection, and medical diagnostics. Three volatile analytes are of particular interest; trimethylamine (TMA) is associated with seafood spoilage and Trimethylaminuria [1], acetic acid (AA) is a biomarker for asthma [2], and ammonia (NH3) is a biomarker for protein degradation [3]. Detection of these molecules requires a highly sensitive and highly specific sensing platform. For the purpose of detecting these molecules, a microcantilever is designed with a nanostructured surface and is functionalized with odorant-binding peptides. The hammerhead microcantilever shown in Figure 1 was designed and fabricated at the Georgia Institute of Technology. The hammerhead shape provides greater surface area and causes the cantilever to resonant in-plane. Nanostructure is fabricated on the microcantilever surface in order to increase the sensitivity of the device. Silicon dioxide nanostructure is created using glancing angle deposition (GLAD) and increases the overall surface area, allowing more molecules to be captured. Images of the nanostructure taken using a high-resolution scanning electron microscope are shown in Figure 2 and 3. The odorant-binding peptides are attached to the SiO2 surface using aminosilane. Validation of the surface chemistry was performed by attaching biotin-streptavadin with a fluorescence tag and viewing under a Fluorescein Isothiocyanate (FITC) light microscope. Further validation is performed by attaching a fluorescence tag to the ammonia-binding peptide and introducing it to a SiO2 surface. Additionally, Raman spectroscopy was used to show the attachment of the silane. The peptides are modeled using the PEP-FOLD servers [4], and binding interactions are modeled using the AutoDock routines in the PyRx software, Figure 4. A scanning Kelvin probe (SKP) is used to demonstrate a charge differential between the flat surface and nanostructure-coated surface. In addition, a charge differential is shown between a surface that is functionalized with peptides and one that is not. This charge differential can be used as a numerical indication of the success of the nanostructure and surface chemistry strategies. The improvement in sensor surface area with added 250 nm nanostructure is estimated to be on the order of a 12-fold increase. BET with Krypton analysis is being used to confirm the amount of nanostructured surface area for both the 250 and 600 nm nanostructure additions. Peptide-functionalized nanostructured cantilevers are being tested for specific VOC molecular binding characteristics. The relevant parameter is the change (decrease) in resonance frequency with added molecular mass. Acknowledgements Research supported by NSF Award #1445488 to KMH. Additional support for RJM provided by the University of Dayton Graduate School.

Multivariate statistical analysis for the identification of potential seafood spoilage indicators

Volatile organic compounds (VOCs) characterize the spoilage of seafood packaged under modified atmospheres (MAs) and could thus be used for quality monitoring. However, the VOC profile typically contains numerous multicollinear compounds and depends on the product and storage conditions. Identification of potential spoilage indicators thus calls for multivariate statistics. The aim of the present study was to define suitable statistical methods for this purpose (exploratory analysis) and to consequently characterize the spoilage of brown shrimp (Crangon crangon) and Atlantic cod (Gadus morhua) stored under different conditions (selective analysis). Hierarchical cluster analysis (HCA), principal components analysis (PCA) and partial least squares regression analysis (PLS) were applied as exploratory techniques (brown shrimp, 4 °C, 50%CO2/50%N2) and PLS was further selected for spoilage marker identification. Evolution of acetic acid, 2,3-butanediol, isobutyl alcohol, 3-methyl-1-butanol, dimethyl sulfide, ethyl acetate and trimethylamine was frequently in correspondence with changes in the microbiological quality or sensory rejection. Analysis of these VOCs could thus enhance the detection of seafood spoilage and the development of intelligent packaging technologies.

Draft Genome Sequence of Serratia proteamaculans MFPA44A14-05, a Model Organism for the Study of Meat and Seafood Spoilage.

ABSTRACTIn this study, we present a draft genome sequence of Serratia proteamaculans MFPA44A14-05. This strain was isolated from a spoiled organic modified-atmosphere-packed beef carpaccio. The draft genome sequence will contribute to the understanding of the role of the S. proteamaculans species in meat and seafood spoilage.

Nanostructured Microcantilevers for the Sensing of Volatile Organic Compounds

Biomolecular detection has applications in many fields, including environmental monitoring, food quality monitoring, hazardous gas detection, and medical diagnostics. Three volatile analytes are of particular interest: trimethylamine (TMA) is associated with seafood spoilage and Trimethylaminuria [1], acetic acid (AA) is a biomarker for asthma [2], and ammonia (NH3) is a biomarker for protein degradation [3]. Detection of these molecules requires a highly sensitive and highly specific sensing platform. For the purpose of detecting these molecules, a microcantilever is designed with a nanostructured surface and is functionalized with odorant-binding peptides. Nanostructure is fabricated on the microcantilever surface in order to increase the sensitivity of the device. Silicon dioxide nanostructure is created using glancing angle deposition (GLAD) and increases the overall surface area, allowing more molecules to be captured. Images of the nanostructure taken using a high-resolution scanning electron microscope are shown in Figure 1. The odorant-binding peptides are attached to the SiO2 surface using aminosilane. Validation of the surface chemistry was performed by attaching biotin-streptavadin with a fluorescence tag (FITC). Further validation is performed by attaching a fluorescence tag to the ammonia-binding peptide and introducing it to a SiO2 surface. The peptides are modeled using the PEP-FOLD servers [4,5], and binding interactions are modeled using the AutoDock routines in the PyRx software, Figure 2. A scanning kelvin probe (SKP) is used to characterize the charge differential between the flat surface and nanostructure-coated surface. In addition, a charge differential is shown between surfaces functionalized with or without peptides. This charge differential can be used as a numerical indication of the success of the nanostructure and surface chemistry strategies.

Antimicrobial seafood packaging: a review.

Microorganisms are the major cause of spoilage in most seafood products; however, only few microbes, called the specific spoilage organisms (SSOs), contribute to the offensive off-flavors associated with seafood spoilage. In food, microbial degradation manifests itself as spoilage, or changes in the sensory properties of a food product, rendering it unsuitable for human consumption. The use of antimicrobial substances can control the general microflora as well as specific microorganisms related to spoilage to provide products with higher safety and better quality. Many antimicrobial compounds have been evaluated in film structures for use in seafood, especially organic acids and their salts, enzymes, bacteriocins; some studies have considered inorganic compounds such as AgSiO2, zinc oxide, silver zeolite, and titanium oxide. The characteristics of some organic antimicrobial packaging systems for seafood and their antimicrobial efficiency in film structures are reviewed in this article.

Genetic diversity analysis of isolates belonging to the Photobacterium phosphoreum species group collected from salmon products using AFLP fingerprinting

An accurate amplified fragment length polymorphism (AFLP) method, including three primer sets for the selective amplification step, was developed to display the phylogenetic position of Photobacterium isolates collected from salmon products. This method was efficient for discriminating the three species Photobacterium phosphoreum, Photobacterium iliopiscarium and Photobacterium kishitanii, until now indistinctly gathered in the P. phosphoreum species group known to be strongly responsible for seafood spoilage. The AFLP fingerprints enabled the isolates to be separated into two main clusters that, according to the type strains, were assigned to the two species P. phosphoreum and P. iliopiscarium. P. kishitanii was not found in the collection. The accuracy of the method was validated by using gyrB-gene sequencing and luxA-gene PCR amplification, which confirmed the species delineation. Most of the isolates of each species were clonally distinct and even those that were isolated from the same source showed some diversity. Moreover, this AFLP method may be an excellent tool for genotyping isolates in bacterial communities and for clarifying our knowledge of the role of the different members of the Photobacterium species group in seafood spoilage.

Comparative Study on Antimicrobial Efficiency of AgSiO2, ZnAg and Ag-Zeolite for the Application of Fishery Plastic Container

AgSiO2, ZnAg and Ag-Zeolite were investigated for antimicrobial activity using Gram-negative Pseudomonas aeruginosa, Shewanella putrefaciens and Gram-positive Clostridium, Listeria monocytogens as target microorganisms by disk diffusion and Agar plate MIC method. These bacteria are responsible for microbiological and chemical spoilage of sea food mainly and from the result we found that Silver zeolite, AgSiO2 has good antimicrobial activity for all target microorganisms except for clostridium perfringem. ZnAg has also shown good antimicrobial properties against all target microorganisms except Listeria monocytogens. Only ZnAg is capable to reduce clostridium perfringem as compare to Silver zeolite and AgSiO2.

Origin and ecological selection of core and food-specific bacterial communities associated with meat and seafood spoilage.

The microbial spoilage of meat and seafood products with short shelf lives is responsible for a significant amount of food waste. Food spoilage is a very heterogeneous process, involving the growth of various, poorly characterized bacterial communities. In this study, we conducted 16S ribosomal RNA gene pyrosequencing on 160 samples of fresh and spoiled foods to comparatively explore the bacterial communities associated with four meat products and four seafood products that are among the most consumed food items in Europe. We show that fresh products are contaminated in part by a microbiota similar to that found on the skin and in the gut of animals. However, this animal-derived microbiota was less prevalent and less abundant than a core microbiota, psychrotrophic in nature, mainly originated from the environment (water reservoirs). We clearly show that this core community found on meat and seafood products is the main reservoir of spoilage bacteria. We also show that storage conditions exert strong selective pressure on the initial microbiota: alpha diversity in fresh samples was 189±58 operational taxonomic units (OTUs) but dropped to 27±12 OTUs in spoiled samples. The OTU assemblage associated with spoilage was shaped by low storage temperatures, packaging and the nutritional value of the food matrix itself. These factors presumably act in tandem without any hierarchical pattern. Most notably, we were also able to identify putative new clades of dominant, previously undescribed bacteria occurring on spoiled seafood, a finding that emphasizes the importance of using culture-independent methods when studying food microbiota.

Assessment of Salmonella and Listeria monocytogenes level in ready-to-cook poultry meat: Effect of various high pressure treatments and potassium lactate concentrations

The objective of this study was to develop a probabilistic model in order to determine the contamination level of Salmonella and Listeria monocytogenes in ready-to-cook poultry meat, after a high pressure (HP) treatment. The model included four steps: i) Reception of raw meat materials, mincing and mixing meat, ii) Partitioning and packaging into 200-g modified atmosphere packs, iii) High pressure treatment of the meat, and iv) Storage in chilled conditions until the end of the shelf-life. The model excluded the cooking step and consumption at consumer's home as cooking practices and heating times are highly variable. The initial contamination level of Salmonella and L. monocytogenes was determined using data collected in meat primary processing plants. The effect of HP treatment and potassium lactate on microbial reduction was assessed in minced meat, using a full factorial design with three high pressure treatments (200, 350 and 500MPa), three holding times (2, 8 and 14min) and two potassium lactate concentrations (0 or 1.8% w/w). The inactivation curves fitted with a Weibull model highlighted that the inactivation rate was significantly dependent on the HP treatment. From the literature, it was established that Salmonella was not able to grow in the presence of lactate, under modified atmosphere and chilled conditions whereas the growth of L. monocytogenes was determined using an existing model validated in poultry (available in Seafood Spoilage and Safety Predictor software, V. 3.1).Once implemented in the Excel add-in @Risk, the model was run using Monte Carlo simulation. The probability distribution of contamination levels was determined for various scenarios. For an average scenario such as an HP treatment of 350MPa for 8min, of 200g minced meat containing 1.8% lactate (pH6.1; aw 0.96), conditioned under 50% CO2, the prevalence rate of Salmonella and L. monocytogenes, after a 20-day storage at 6°C was estimated to be 4.1% and 7.1%, respectively. The contamination level was low considering that the product is going to be cooked by the consumer afterwards: the 99th percentile of the distribution was equal to −2.3logcfu/g for Salmonella and 0.5logcfu/g for L. monocytogenes. More generally, the model developed here from raw material reception up to the end of the shelf-life enables to recommend combinations of HP treatment and lactate formulation to guarantee an acceptable microbial concentration before cooking.

Volatile compounds associated with Psychrobacter spp. and Pseudoalteromonas spp., the dominant microbiota of brown shrimp (Crangon crangon) during aerobic storage

The spoilage potential of several Psychrobacter and Pseudoalteromonas species (Psychrobacter cibarius, Psychrobacter maritimus, Pseudoalteromonas elyakovii, Pseudoalteromonas paragorgicola and Pseudoalteromonas nigrifaciens) was determined and quantified based on the presence of volatile organic compounds (VOCs). Psychrobacter and Pseudoalteromonas species dominate the microbiota of cooked brown shrimp (Crangon crangon). Additionally, API ZYM analyses determined the species' enzymatic capacity to contribute to spoilage by degrading lipids, amino acids and proteins. The bacterial species used in this study were isolated from cooked brown shrimp during storage under different storage and processing conditions and were selected for analysis of their spoilage potential based on their difference in the (GTG)5-rep profile, 16S rRNA and gyrB sequences and API ZYM profile. The isolates were inoculated as pure cultures on heat-sterilised shrimp. The inoculated samples were stored at 4°C and the production of VOCs by the pure strains on the shrimp matrix was identified via gas chromatography coupled to mass spectrometry (GC–MS). VOC production was quantified daily by selected ion flow tube mass spectrometry (SIFT-MS) until the bacterial count exceeded 108–109cfu/g. The sensory profile of Psychrobacter species revealed very low spoilage potential as measured by the production of VOCs, but these species may nevertheless contribute to spoilage. Based on the API ZYM results, Pseudoalteromonas as well as Psychrobacter species might enhance spoilage by breaking down lipids and hydrolysing amino acids and proteins. Pseudoalteromonas species, especially Psa. elyakovii and Psa. nigrifaciens, have a high spoilage potential and might be responsible for the off-odours produced during spoilage of brown shrimp. These isolates produced significant amounts of volatile compounds such as sulphides, acetone, ammonia, and ethanol, which are all involved in seafood spoilage.

Effects of chilled storage on quality of vacuum packed meagre fillets

The aim of this study was to experimentally assess several quality indices of meagre Argyrosomus regius (Asso, 1801) fillets packed in air (AP) and vacuum (VP) stored chilled (+4°C) for up to 13days. Considering our experimental data on concentration of bacterial counts, shelf-life is estimated at ca. 6days for AP fillets and an additional 3–5days for VP meagre fillets. Total volatile basic nitrogen (TVB-N) and trimethylamine (TMA-N) did not reach the regulated limits (25–35mg/100g chilled fish). The models implemented in the software Seafood Spoilage and Safety Predictor predicted a relatively shorter shelf-life of 4.8–6.9days for fish stored in air at +4°C when compared to AP and VP fillets. Empirical data and the models implemented in the software were used to predict the shelf-life of fillets if packaged under different modified atmospheres (MAP). Chilled, MAP fillets are likely to have a longer shelf-life than AP or VP samples if equilibrium CO2 concentration is substantially high.