Qualitative and quantitative characterization of spoilage bacteria from packed fish

Discovering microbiota and volatile compounds of surströmming, the traditional Swedish sour herring

In this study, the microbiota of ready-to-eat surströmming from three Swedish producers were studied using a combined approach. The pH values of the samples ranged between 6.67 ± 0.01 and 6.98 ± 0.01, whereas their a_w values were between 0.911 ± 0.001 and 0.940 ± 0.001. The acetic acid concentration was between 0.289 ± 0.009 g/100 g and 0.556 ± 0.036 g/100 g. Very low concentrations of lactic acid were measured. Viable counting revealed the presence of mesophilic aerobes, mesophilic lactobacilli and lactococci as well as halophilic lactobacilli and lactococci, coagulase-negative staphylococci, halophilic aerobes and anaerobes. Negligible counts for Enterobacteriaceae, Pseudomonadaceae and total eumycetes were observed, whereas no sulfite-reducing anaerobes were detected. Listeria monocytogenes and Salmonella spp. were absent in all samples. Multiplex real-time PCR revealed the absence of the bont/A, bont/B, bont/E, bont/F, and 4gyrB (CP) genes, which encode botulinic toxins, in all the samples analyzed. Metagenomic sequencing revealed the presence of a core microbiota dominated by Halanaerobium praevalens, Alkalibacterium gilvum, Carnobacterium spp., Tetragenococcus halophilus, Clostridiisalibacter spp. and Porphyromonadaceae. Psychrobacter celer, Ruminococcaceae, Marinilactibacillus psychrotolerans, Streptococcus infantis and Salinivibrio costicola were detected as minor OTUs. GC-MS analysis of volatile components revealed the massive presence of trimethylamine and sulphur compounds. Moreover, 1,2,4-trithiolane, phenols, ketones, aldehydes, alcohols, esters and long chain aliphatic hydrocarbons were also detected. The data obtained allowed pro-technological bacteria, which are well-adapted to saline environments, to be discovered for the first time. Further analyses are needed to better clarify the extent of the contribution of either the microbiota or autolytic enzymes of the fish flesh in the aroma definition.

Extraction, Identification, Modification, and Antibacterial Activity of Histone from Immature Testis of Atlantic salmon

In the present study, histone from immature testis of Atlantic salmon was extracted and identified, and its antibacterial activity after enzymolysis was investigated. Histone extracted from Atlantic salmon (Salmo salar) testis using the acid extraction method was successfully identified by LC-MS/MS, and revealed significant inhibitory activity on both the Gram-negative and Gram-positive bacteria. With a low concentration of 10 mg/mL, the observed inhibitory zone diameter (IZD) could significantly reach up to 15.23 mm. After modification of enzymatic hydrolysis by pepsin, histone could be digested to three fragments, while the antibacterial activity increased up to 57.7%. All the results suggested the leftovers from commercial fishing could be utilized for the extraction of antimicrobial peptides.

Assessment of Spoilage Bacterial Communities in Food Wrap and Modified Atmospheres-Packed Minced Pork Meat Samples by 16S rDNA Metagenetic Analysis

Although several studies have focused on the dynamics of bacterial food community, little is known about the variability of batch production and microbial changes that occur during storage. The aim of the study was to characterize the microbial spoilage community of minced pork meat samples, among different food production and storage, using both 16S rRNA gene sequencing and classical microbiology. Three batches of samples were obtained from four local Belgian facilities (A–D) and stored until shelf life under food wrap (FW) and modified atmosphere packaging (MAP, CO₂ 30%/O₂ 70%), at constant and dynamic temperature. Analysis of 288 samples were performed by 16S rRNA gene sequencing in combination with counts of psychrotrophic and lactic acid bacteria at 22°C. At the first day of storage, different psychrotrophic counts were observed between the four food companies (Kruskal-Wallist test, p-value < 0.05). Results shown that lowest microbial counts were observed at the first day for industries D and A (4.2 ± 0.4 and 5.6 ± 0.1 log CFU/g, respectively), whereas industries B and C showed the highest results (7.5 ± 0.4 and 7.2 ± 0.4 log CFU/g). At the end of the shelf life, psychrotrophic counts for all food companies was over 7.0 log CFU/g. With metagenetics, 48 OTUs were assigned. At the first day, the genus Photobacterium (86.7 and 19.9% for food industries A and C, respectively) and Pseudomonas (38.7 and 25.7% for food companies B and D, respectively) were dominant. During the storage, a total of 12 dominant genera (>5% in relative abundance) were identified in MAP and 7 in FW. Pseudomonas was more present in FW and this genus was potentially replaced by Brochothrix in MAP (two-sided Welch’s t-test, p-value < 0.05). Also, a high Bray-Curtis dissimilarity in genus relative abundance was observed between food companies and batches. Although the bacteria consistently dominated the microbiota in our samples are known, results indicated that bacterial diversity needs to be addressed on the level of food companies, batches variation and food storage conditions. Present data illustrate that the combined approach provides complementary results on microbial dynamics in minced pork meat samples, considering batches and packaging variations.

Involvement of Exogenous N-Acyl-Homoserine Lactones in Spoilage Potential of Pseudomonas fluorescens Isolated From Refrigerated Turbot

Some bacteria can modulate their spoilage potential by responding to environmental signaling molecules via the quorum sensing (QS) system. However, the ability of Pseudomonas fluorescens, the specific spoilage organism (SSO) of turbot, to response to environmental signaling molecules remains unclear. This study investigated the effects of six synthetic N-acyl homoserine lactones (AHLs) on typical behaviors mediated by QS in P. fluorescens, such as biofilm formation and extracellular protease activity. Total volatile basic nitrogen (TVB-N) was used as a spoilage indicator to evaluate quality changes in AHL-treated turbot filets during storage. The results confirm the enhancing effect of environmental AHLs on QS-dependent factors of P. fluorescens and quality deterioration of turbot filets, with C₄-HSL and C₁₄-HSL being the most effective. Moreover, the content decrease of exogenous AHLs was also validated by gas chromatography–mass spectrometry analysis. Further, changes in rhlR transcription levels in P. fluorescens suggest that this bacterium can sense environmental AHLs. Finally, molecular docking analysis demonstrates the potential interactions of RhlR protein with various exogenous AHLs. These findings strongly implicate environmental AHLs in turbot spoilage caused by P. fluorescens, suggesting preservation of turbot should not exclusively consider the elimination of SSO-secreted AHLs.

Predictive Modeling of Microbial Behavior in Food

Microorganisms can contaminate food, thus causing food spoilage and health risks when the food is consumed. Foods are not sterile; they have a natural flora and a transient flora reflecting their environment. To ensure food is safe, we must destroy these microorganisms or prevent their growth. Recurring hazards due to lapses in the handling, processing, and distribution of foods cannot be solved by obsolete methods and inadequate proposals. They require positive approach and resolution through the pooling of accumulated knowledge. As the industrial domain evolves rapidly and we are faced with pressures to continually improve both products and processes, a considerable competitive advantage can be gained by the introduction of predictive modeling in the food industry. Research and development capital concerns of the industry have been preserved by investigating the plethora of factors able to react on the final product. The presence of microorganisms in foods is critical for the quality of the food. However, microbial behavior is closely related to the properties of food itself such as water activity, pH, storage conditions, temperature, and relative humidity. The effect of these factors together contributing to permitting growth of microorganisms in foods can be predicted by mathematical modeling issued from quantitative studies on microbial populations. The use of predictive models permits us to evaluate shifts in microbial numbers in foods from harvesting to production, thus having a permanent and objective evaluation of the involving parameters. In this vein, predictive microbiology is the study of the microbial behavior in relation to certain environmental conditions, which assure food quality and safety. Microbial responses are evaluated through developed mathematical models, which must be validated for the specific case. As a result, predictive microbiology modeling is a useful tool to be applied for quantitative risk assessment. Herein, we review the predictive models that have been adapted for improvement of the food industry chain through a built virtual prototype of the final product or a process reflecting real-world conditions. It is then expected that predictive models are, nowadays, a useful and valuable tool in research as well as in industrial food conservation processes.

Involvement of Exogenous N-Acyl-Homoserine Lactones in Spoilage Potential of Pseudomonas fluorescens Isolated From Refrigerated Turbot

Some bacteria can modulate their spoilage potential by responding to environmental signaling molecules via the quorum sensing (QS) system. However, the ability of Pseudomonas fluorescens, the specific spoilage organism (SSO) of turbot, to response to environmental signaling molecules remains unclear. This study investigated the effects of six synthetic N-acyl homoserine lactones (AHLs) on typical behaviors mediated by QS in P. fluorescens, such as biofilm formation and extracellular protease activity. Total volatile basic nitrogen (TVB-N) was used as a spoilage indicator to evaluate quality changes in AHL-treated turbot filets during storage. The results confirm the enhancing effect of environmental AHLs on QS-dependent factors of P. fluorescens and quality deterioration of turbot filets, with C₄-HSL and C₁₄-HSL being the most effective. Moreover, the content decrease of exogenous AHLs was also validated by gas chromatography-mass spectrometry analysis. Further, changes in rhlR transcription levels in P. fluorescens suggest that this bacterium can sense environmental AHLs. Finally, molecular docking analysis demonstrates the potential interactions of RhlR protein with various exogenous AHLs. These findings strongly implicate environmental AHLs in turbot spoilage caused by P. fluorescens, suggesting preservation of turbot should not exclusively consider the elimination of SSO-secreted AHLs.

Characterization of the Spoilage Microbiota of Hake Fillets Packaged Under a Modified Atmosphere (MAP) Rich in CO2 (50% CO2/50% N2) and Stored at Different Temperatures

The aim of this study was to characterize the spoilage microbiota of hake fillets stored under modified atmospheres (MAP) (50% CO₂/50% N₂) at different temperatures using high-throughput 16S rRNA gene sequencing and to compare the results with those obtained using traditional microbiology techniques. The results obtained indicate that, as expected, higher storage temperatures lead to shorter shelf-lives (the time of sensory rejection by panelists). Thus, the shelf-life decreased from six days to two days for Batch A when the storage temperature increased from 1 to 7 °C, and from five to two days—when the same increase in storage temperature was compared—for Batch B. In all cases, the trimethylamine (TMA) levels measured at the time of sensory rejection of hake fillets exceeded the recommended threshold of 5 mg/100 g. Photobacterium and Psychrobacter were the most abundant genera at the time of spoilage in all but one of the samples analyzed: Thus, Photobacterium represented between 19% and 46%, and Psychrobacter between 27% and 38% of the total microbiota. They were followed by Moritella, Carnobacterium,Shewanella, and Vibrio, whose relative order varied depending on the sample/batch analyzed. These results highlight the relevance of Photobacterium as a spoiler of hake stored in atmospheres rich in CO₂. Further research will be required to elucidate if other microorganisms, such as Psychrobacter, Moritella, or Carnobacterium, also contribute to spoilage of hake when stored under MAP.

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.

Characterization of Bacterial Microbiota in Tilapia Fillets Under Different Storage Temperatures

This paper investigates the bacterial microbiota in tilapia fillets under cold (4 °C), iced (0 °C), and superchilled (-3 °C) storage conditions. At 4 °C, at least seven species/strains of Pseudomonas were detected in the fillets, five of which were dominant either at a certain stage or throughout the entire storage period. Shewanella was less dominant than Pseudomonas at 4 °C, while Serratia became dominant after 6 days storage at 4 °C. The microbiota in fillets stored at 0 and -3 °C were very similar and rarely changed during storage, yet differed greatly from the microbiota at 4 °C. Only two Pseudomonas species/strains grew at 0 and -3 °C, one of which was the most dominant. A Vibrionimonas sp. not found at 4 °C was found to be the second most dominant species at 0 and -3 °C. Shewanella and Psychrobacter were also present at 0 and -3 °C but were the minor genera. The most dominant strains at -3, 0, and 4 °C were separately isolated and subjected to full length 16S rDNA sequencing, which demonstrated that they were identical and were Pseudomonas fluorescens. The changes of the total bacterial count and TVBN value of the fillets inoculated with the isolated P. fluorescens were very similar to those of fillets with natural microbiota. This implies that P. fluorescens is the most important spoiler of tilapia fillets at -3, 0, or 4 °C. PRACTICAL APPLICATION: This research shows that fewer species of bacteria survive at 0 and -3 °C than those at 4 °C, while among these bacteria, the most important spoiler is P. fluorescens. This may provide some clues to extend the shelf life of tilapia fillets by taking some inhibitory measures targeted at P. fluorescens in the future.

Inhibition of Biogenic Amines in Shewanella baltica by Anthocyanins Involving a Quorum Sensing System

HIGHLIGHTS

Put was the main biogenic amine produced by Shewanella baltica. PL and PP were the main QS autoinducers of S. baltica. PL and PP displayed significant positive correlation with Put. DKPs and Put production and odc gene expression were inhibited by anthocyanins. Anthocyanins were proposed as new QSIs and seafood preservative candidates.

Characterization of the Microbiota in Air- or Vacuum-Packed Crisp Grass Carp ( Ctenopharyngodon idella C. et V.) Fillets by 16S rRNA PCR-Denaturing Gradient Gel Electrophoresis and High-Throughput Sequencing

The microbial communities in air- and vacuum-packed crisp grass carp ( Ctenopharyngodon idella C. et V.) fillets have not been characterized during chilled storage. High-throughput sequencing of bacterial 16S rRNA has now revealed that the bacterial community in fresh fillets is diverse and distinct from that in spoiled samples. The predominant phylum was Proteobacteria, and 66 genera were identified. In fresh fillets, the most abundant genera were Acinetobacter (53.3%), Wautersiella (6.3%), unclassified Alcaligenaceae (4.4%), Stenotrophomonas (3.8%), unclassified Enterobacteriaceae (3.8%), and Enhydrobacter (3.6%). These genera diminished during chilled storage and sometimes disappeared. At the end of storage, Aeromonas and Pseudomonas were the most abundant. Similar results were obtained by PCR-denaturing gradient gel electrophoresis. These data provide detailed insight into the evolving bacterial communities in air- and vacuum-packed crisp grass carp fillets during storage, revealing Aeromonas and Pseudomonas as major spoilage organisms. These data may be useful for improvement of crisp grass carp quality and shelf life during chilled storage.

Identification of spoilage microorganisms in blueberry juice and their inactivation by a microchip pulsed electric field system

Blueberry juice is a healthy and nutritious food that has become increasingly popular worldwide. However, little is known about the microbial groups of this juice that can cause its spoilage. This study aimed to identify the main spoilage microorganisms in blueberry juice and explore whether a microchip pulsed electric field (MPEF) can effectively inactivate them. We performed polymerase chain reaction (PCR) amplification, as well as 16S rDNA, 18S rDNA, internal transcribed spacer (ITS), and 26S rDNA gene sequence analyses. Nine species belonging to eight genera, including Pantoea, Burkholderia, Pichia, Meyerozyma, Cryptococcus, Aureobasidium, Cladosporium, and Penicillium were identified as spoilage microorganisms. Cryptococcus sp., Meyerozyma sp., and Pichia sp. were specific spoilage organisms (SSO) owing to their rising numbers throughout spoilage progression. The effect of MPEF on the potential inactivation of these microorganisms was to induce significant inactivation of viable Cryptococcus sp., Meyerozyma sp., and Pichia sp. This research provides a theoretical basis for the application of MPEF in improving the quality of blueberry juice.

Improved intracellular PHA determinations with novel spectrophotometric quantification methodologies based on Sudan black dye

The presence of intracellular polyhydroxyalkanoates (PHAs) is usually studied using Sudan black dye solution (SB). In a previous work it was shown that the PHA could be directly quantified using the absorbance of SB fixed by PHA granules in wet cell samples. In the present paper, the optimum SB amount and the optimum conditions to be used for SB assays were determined following an experimental design by hybrid response surface methodology and desirability-function. In addition, a new methodology was developed in which it is shown that the amount of SB fixed by PHA granules can also be determined indirectly through the absorbance of the supernatant obtained from the stained cell samples. This alternative methodology allows a faster determination of the PHA content (involving 23 and 42 min for indirect and direct determinations, respectively), and can be undertaken by means of basic laboratory equipment and reagents. The correlation between PHA content in wet cell samples and the spectra of the SB stained supernatant was determined by means of multivariate and linear regression analysis. The best calibration adjustment (R² = 0.91, RSE: 1.56%), and the good PHA prediction obtained (RSE = 1.81%), shows that the proposed methodology constitutes a reasonably precise way for PHA content determination. Thus, this methodology could anticipate the probable results of the above mentioned direct PHA determination. Compared with the most used techniques described in the scientific literature, the combined implementation of these two methodologies seems to be one of the most economical and environmentally friendly, suitable for rapid monitoring of the intracellular PHA content.

Effects of chitosan oligosaccharides on microbiota composition of silver carp (Hypophthalmichthys molitrix) determined by culture-dependent and independent methods during chilled storage

This study evaluated the effects of chitosan oligosaccharides (COS) on the changes in quality and microbiota of silver carp fillets stored at 4 °C. During storage, 1% (w/v) COS treated samples maintained good quality, as evidenced by retarding sensory deterioration, inhibiting microbial growth, attenuating the production of total volatile basic nitrogen, putrescine, cadaverine and hypoxanthine, and delaying degradation of inosine monophosphate and hypoxanthine ribonucleotide. Meanwhile, variability in the predominant microbiota in different samples was investigated by culture-dependent and -independent methods. Based on sensory analysis, shelf-life of silver carp fillets was 4 days for the control and 6 days for COS treated samples. Meanwhile, Pseudomonas, followed by Aeromonas, Acinetobacter, and Shewanella were dominated in the control samples at day 4 and contributed to fish spoilage at day 6. However, COS inhibited the growth of Pseudomonas, Aeromonas, and Shewanella significantly. Consequently, Acinetobacter followed by Pseudomonas became the predominant microbiota in COS treated samples at day 6. With the growth of Pseudomonas, COS treated samples were spoiled at day 8. Therefore, COS improved the quality of fillets and prolonged the shelf life of silver carp fillets by 2 days during chilled storage, which was mainly due to their modulating effects on microbiota.

Seafood spoilage microbiota and associated volatile organic compounds at different storage temperatures and packaging conditions

Seafood comprising of both vertebrate and invertebrate aquatic organisms are nutritious, rich in omega-3 fatty acids, essential vitamins, proteins, minerals and form part of healthy diet. However, despite the health and nutritional benefits, seafood is highly perishable. Spoilage of seafood could be as a result of microbial activity, autolysis or chemical oxidation. Microbial activity constitutes more spoilage than others. Spoilage bacteria are commonly Gram negative and produce off odours and flavours in seafood as a result of their metabolic activities. Storage temperature, handling and packaging conditions affect microbial growth and thus the shelf-life of seafood. Due to the complexity of the microbial communities in seafood, culture dependent methods of detection may not be useful, hence the need for culture independent methods are necessary to understand the diversity of microbiota and spoilage process. Similarly, the volatile organic compounds released by spoilage bacteria are not fully understood in some seafood. This review therefore highlights current knowledge and understanding of seafood spoilage microbiota, volatile organic compounds, effects of storage temperature and packaging conditions on quality of seafood.

Development of a MALDI-TOF MS-Based Protein Fingerprint Database of Common Food Fish Allowing Fast and Reliable Identification of Fraud and Substitution

Fish substitution and fish fraud are widely observed in the global food market. To detect and prevent substitution, DNA-based methods do not always meet the demand of being time- and cost-efficient; therefore, methodology improvements are needed. The use of species-specific protein patterns, as determined by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry, has recently improved species identification of prokaryotes both time- and cost-wise. We used the method to establish a database containing protein patterns of common food fish prone to substitution. The database currently comprises 54 fish species. Aspects such as the sensitivity of identification on the species level and the impact of bacterial contamination of fish filets are assessed. Most database entries are characterized by low intraspecies but high interspecies variability. Hitherto, 118 validation samples were successfully determined. The results presented herein underline the potential and reliability of eukaryotic species identification via MALDI-TOF mass spectrometry.

Comparing the effects of different dietary organic acids on the growth, intestinal short-chain fatty acids, and liver histopathology of red hybrid tilapia (Oreochromis sp.) and potential use of these as preservatives

Dietary organic acids are increasingly being investigated as a potential means of improving growth and nutrient utilization in aquatic animals. A 9-week study was performed to compare equal amounts (2%) of different organic acids (sodium butyrate, acetate, propionate, or formate) on the growth, muscle proximate composition, fatty acid composition, cholesterol and lipid peroxidation, differential cell counts, plasma biochemistry, intestinal short-chain fatty acid (SCFA) level, and liver histopathology to red hybrid tilapia (Oreochromis sp.) (initial mean weight of 2.87 g). A second experiment was performed to determine their effects on lipid peroxidation and trimethylamine (TMA) when added at 1% to tilapia meat and left out for 24 h. The results of the first experiment showed no treatment effect to growth, feeding efficiencies, or muscle fatty acid composition, but all dietary organic acids significantly decreased intestinal SCFA. Dietary butyrate and propionate significantly decreased muscle lipid peroxidation compared to the control group, but the dietary formate treatment had the lowest lipid peroxidation compared to all treatments. Muscle crude protein and lipid in tilapia fed the formate diet were significantly lower and higher, respectively, and showed evidence of stress based on the differential cell counts, significantly higher plasma glucose and liver glycogen, as well as inflammatory responses in the liver. Although a potential benefit of dietary organic acids was a reduction to lipid peroxidation, this could be accomplished post-harvest by direct additions to the meat. In addition, inclusions of butyrate and propionate to tilapia meat significantly decreased TMA, which might be a more cost-effective option to improve the shelf life of tilapia products.

Introducing a Novel Media to Improve the Recovery of Culturable Bacteria from the Fish Parasite Anisakis spp. larvae (Nematoda: Anisakidae)

This paper describes a cultivation method to increase the recovery of bacteria from the marine muscle-invading parasitic nematode larvae of Anisakis spp. These larvae hold a high and complex population of accumulated bacteria, originating from seawater, crustaceans, fish, and marine mammals, all involved in the lifecycle of Anisakis. Two in-house agars based on fish juice prepared by either mechanical or enzymatic degradation of the fish tissue, were made. The Anisakis larvae were homogenised prior to cultivation on the in-house fish juice agars and the bacterial numbers and diversity were compared to those obtained applying the commercially available Marine Agar and Iron Agar Lyngby. Bacterial colonies of unique appearance were subcultured and identified by 16S rRNA gene sequencing. Totally three of twenty identified taxa were found on the in-house fish juice agars only. Fish juice agar prepared enzymatically would be the best supplementary agar, as this agar gave significantly higher heterotrophic plate counts, compared to mechanical preparation. The enzymatically prepared fish juice gave more suitable agar quality, was more resource efficient, and had apparently increased nutrient density and availability.

Identification and Quantification of Acylated Homoserine Lactones in Shewanella baltica, the Specific Spoilage Organism of Pseudosciaena crocea, by Ultrahigh-Performance Liquid Chromatography Coupled to Triple Quadrupole Mass Spectrometry

Bacteria communicate with one another using chemical signal molecules called autoinducers, and the most prevalent autoinducers used by Gram-negative bacteria are N-acylated homoserine lactones (AHLs). However, AHLs are hardly detected in Shewanella baltica, the specific spoilage organism of Pseudosciaena crocea. In this study, we applied ultrahigh-performance liquid chromatography coupled to triple quadrupole tandem mass spectrometry to determine AHLs. This method enabled the quantification of up to 11 AHLs within 5.6 min with excellent sensitivity (ng/mL level) and linearity (r² > 0.99), which further detected 9 AHLs produced by S. baltica. Furthermore, by using a biofilm formation assay and statistical analysis, the biofilm-inducing activity of AHL in S. baltica was first revealed. Our results elucidated the physiological role of AHL in S. baltica and provided a satisfactory method to detect AHLs and a statistical model to predict food spoilage properties.

Characterization of the microbiota in lightly salted bighead carp (Aristichthys nobilis) fillets stored at 4 °C

The microbiota of unsalted and salted (dry-cured with 2% salt) bighead carp (Aristichthys nobilis) fillets during storage at 4 °C were identified by 16S rRNA gene analysis. Eleven genera were present in the initial microbiota of bighead carp fillets, where Acinetobacter, Aeromonas and Kocuria were the dominant bacteria. As storage time progressed, the microbial composition of both unsalted and salted fillets became less diverse. Additionally, differences in microbiota were observed between these two treatments. For unsalted bighead carp fillets, Aeromonas became the dominant genus at the end of storage and Pseudomonas was found less commonly. For salted fillets, Pseudomonas was the only bacteria identified at the end of storage.

Lactococcus piscium: a psychrotrophic lactic acid bacterium with bioprotective or spoilage activity in food-a review

The genus Lactococcus comprises 12 species, some known for decades and others more recently described. Lactococcus piscium, isolated in 1990 from rainbow trout, is a psychrotrophic lactic acid bacterium, probably disregarded because most of the strains are unable to grow at 30°C. During the last 10 years, this species has been isolated from a large variety of food: meat, seafood and vegetables, mostly packed under vacuum (VP) or modified atmosphere (MAP) and stored at chilled temperature. Recently, culture-independent techniques used for characterization of microbial ecosystems have highlighted the importance of Lc. piscium in food. Its role in food spoilage varies according to the strain and the food matrix. However, most studies have indicated that Lc. piscium spoils meat, whereas it does not degrade the sensory properties of seafood. Lactococcus piscium strains have a large antimicrobial spectrum, including Gram-positive and negative bacteria. In various seafoods, some strains have a protective effect against spoilage and can extend the sensory shelf-life of the products. They can also inhibit the growth of Listeria monocytogenes, by a cell-to-cell contact-dependent. This article reviews the physiological and genomic characteristics of Lc. piscium and discusses its spoilage or protective activities in food.