Metagenomic, microbial, chemical and sensory analyses of Thunnus albacares from Martinique stored in ice (AIR – 0 °C), vacuum (VP – 4/8 °C) and modified atmosphere packaging (MAP – 4/8 °C) (70% CO2 – ...30% O2) were carried out. The organoleptic rejection of AIR tuna was observed at day 13 when total bacterial counts equaled 106–107 CFU g−1. No extension of shelf-life was provided by VP and MAP. According to 16S rRNA gene sequence analyzed by Illumina MiSeq and PCR-TTGE, Rhodanobacter terrae was the main species of the freshly caught tuna. At the sensory rejection time, Brochothrix thermosphacta and Pseudomonas dominated the AIR products while B. thermosphacta alone or a mix of B. thermosphacta, Enterobacteriaceae and lactic acid bacteria (LAB) dominated the microbiota of MAP and VP products, respectively. The pH value remained stable in all trials, ranging from 5.77 to 5.97. Total volatile basic nitrogen (TVBN) and trimethylamine (TMA-N) concentrations were weak and not significantly different between batches. Lipid oxidation increased in the samples containing O2 (MAP > AIR). The initial concentration of histamine was high (75–78 mg kg−1) and stable up to 8 days but then significantly decreased in all trials to reach 25–30 mg kg−1, probably due to the presence of histamine-decomposing bacteria.
The spoilage potential of eight bacterial groups/species (Serratia spp., Hafnia alvei, Brochothrix thermosphacta, Carnobacterium maltaromaticum, Shewanella baltica, Lactococcus piscium, ...Photobacterium phosphoreum, “other Enterobacteriaceae” containing one strain of Moellerella sp., Morganella sp. and Pectobacterium sp.) isolated from spoiled raw salmon fillets stored under modified atmosphere packaging (MAP) was evaluated by inoculation into sterile raw salmon cubes followed by storage for 12days at 8°C. Microbial growth and sensory changes were monitored during the storage period. The dominant spoilage bacteria were C. maltaromaticum, H. alvei and P. phosphoreum. In order to further characterize their spoilage potential and to study the effect of their interactions, each of these 3 specific spoilage organisms (SSO) and two mixed-cultures, C. maltaromaticum/H. alvei and C. maltaromaticum/P. phosphoreum were tested in the sterile salmon model system using a combination of complementary methods: molecular (PCR-TTGE), sensory, chemical and conventional microbiological analyses. It was concluded that, in the mixed-culture inoculated samples, the dominant species determined the spoilage characteristics. The volatile fraction of P. phosphoreum inoculated samples was analyzed by solid-phase microextraction (SPME) followed by gas chromatography coupled to mass spectrometry (GC–MS). Among the specific volatile compounds present on P. phosphoreum spoiled inoculated samples, acetic acid was correlated with sensory analysis and can be proposed as a raw salmon spoilage marker.
► Spoilage potential of 8 bacterial groups isolated from spoiled salmon was evaluated. ► Specific spoilage organisms were identified among these bacterial groups. ► Spoilage abilities and bacterial interactions of 3 dominant spoilers were further characterized. ► On mixed-culture inoculated samples, spoilage characteristics are imposed by the dominant species.
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.
Biopreservation is a natural technology of food preservation, which consists of inoculating food with microorganisms selected for their antibacterial properties. The objective of this study was to ...select lactic acid bacteria (LAB) to improve the quality of cold-smoked salmon (CSS). In this work, different strains representative of the 4 dominant species, identified in a previous study by pyrosequencing the 16S rRNA gene, were isolated and their spoiling potential in CSS blocks, sterilized by ionization, was assessed by twelve trained panelists along the vacuum storage at 8°C. Photobacterium phosphoreum, Brochothrix thermosphacta and Serratia proteamaculans released strong off-odors whereas the spoiling potential of Carnobacterium divergens was weaker. The spoiling capacity of Lactococcus piscium EU2241, Leuconostoc gelidum EU2247, Lactobacillus sakei EU2885, Staphylococcus equorum S030674 and 4 commercial starters was tested by the same method and 2 strains were eliminated due to off-odor production. The effect of the 6 selected LAB against the 4 specific spoiling organisms (SSOs) selected was tested by challenge tests in sterile CSS blocks. The protective effect of the LAB differed from one SSO to another and no correlation could be established between the sensory improvement, SSO inhibition, and the implantation or acidification of protective cultures (PCs). All the PCs except L. piscium reduced the off-odors released by P. phosphoreum although some of them had no effect on its growth. S. equorum, which did not grow in CSS, favored the implantation of P. phosphoreum but prevented its off-odor formation. L. piscium was the only strain that prevented the spoilage of B. thermosphacta and S. proteamaculans although it did not grow very well and did not acidify the product. L. gelidum EU2247 inhibited the growth of these 2 SSOs and lowered the pH but had no effect on the sensory quality. Finally, L. piscium was tested in 2 naturally contaminated products, with a positive effect on 1 batch. This effect was not correlated with the microbial ecosystem as determined by acultural and cultural techniques. Based on these results, the selection strategy is discussed.
•Four specific spoilage bacteria of cold-smoked salmon were identified.•Eight protective cultures were tested in situ against the four spoilage bacteria.•Lactococcus piscium EU2241 improved the sensory quality of cold-smoked salmon.•There was no correlation between sensory improvement and microbial ecosystem.
Tropical shrimp is of considerable economic importance in the world but is highly perishable due to microbial and chemical degradation. Biopreservation is a food preservation technology based on the ...addition of “positive” bacteria able to kill or prevent the growth of undesirable microorganisms. Two strains of lactic acid bacteria (LAB) have previously been selected for a biopreservation strategy: Lactococcus piscium CNCM I-4031, for its ability to prevent the sensory deterioration of seafood and Carnobacterium divergens V41, which inhibits growth of Listeria monocytogenes. The objective was to test the association of the two strains to improve both the quality and safety of shrimp. In a first trial, the two LAB were inoculated alone or in a cocktail in cooked and peeled shrimp (CPS) Penaeus vannamei at 5×105CFU/g. Chemical, sensory and microbiological analyses by culture-dependent and -independent methods were performed during storage under modified atmosphere packaging (MAP) at 8°C. The results were compared to a non-inoculated batch. In a second trial, the same experiments were repeated in the presence of 102CFU/g of L. monocytogenes RF191. The microbiota of CPS was composed of LAB, Shewanella spp. and Enterobacteriaceae. Brochothrix thermosphacta was not detected. L. piscium and C. divergens reached 108 and 109CFU/g, respectively, in 7days and did not inhibit each other when co-inoculated. L. piscium reduced L. monocytogenes by 1Log (CFU/g) for 28days. C. divergens had an immediate listericidal effect lasting 7days. A regrowth of L. monocytogenes was then observed but the count was always 2 to 5Log (CFU/g) lower than in the control. No additional or synergic effect between protective strains was observed and the cocktail had the same inhibitory effect as C. divergens alone. C. divergens was very effective at preventing the sensory deterioration of CPS. This may be related to the inhibition of Shewanella and Enterobacteriaceae. However, the panelists could detect the presence of C. divergens during the first 10days of storage, with slight unpleasant odors and flavors. L. piscium improved the sensory quality of CPS for 14days only. In co-culture, L. piscium eliminated the off-odors and flavors released by C. divergens in the early stage of storage and the co-culture allowed maintaining a good quality of CPS throughout the storage. Therefore, the use of a cocktail of L. piscium CNCM I-4031 and C. divergens V41 is recommended in a strategy of biopreservation of shrimp.
•A cocktail of L. piscium and C. divergens was tested to biopreserve cooked shrimp.•L. piscium CNCM-I4031 and C. divergens V41 have no antagonist effect on each other.•L. piscium inhibited L. monocytogenes by 1Log and C. divergens by 2 to 5Log CFU/g.•The cocktail showed no additional or synergetic effect on inhibition of Listeria.•The cocktail was more efficient to improve sensory quality than the strains alone.
In order to characterise the spoilage related to microbiota of raw salmon, a combination of culture-dependent and -independent methods, including PCR–TTGE, was used to analyse 3 raw salmon batches ...stored for 3 days at chilled temperature in modified atmosphere packaging (MAP) (50% CO2/50% N2) or under vacuum. Sensory evaluation, microbiological enumeration and chemical analysis were performed after 3, 7 and 10 days of storage. At the onset of spoilage, 65 bacterial isolates were picked from the plates. Thus, 13 different genera or species were identified by phenotypic and molecular tests: Serratia spp., Photobacterium phosphoreum, Yersinia intermedia, Hafnia alvei, Buttiauxella gaviniae, Pseudomonas sp., Carnobacterium maltaromaticum, Carnobacterium divergens, Lactococcus piscium, Lactobacillus fuchuensis, Vagococcus carniphilus, Leuconostoc gasicomitatum and Brochothrix thermosphacta. The PCR–TTGE profiles and band identification enabled a shift of the dominant populations during the storage to be visualised for all the batches, probably due to the temperature change and the packaging. At the beginning of storage, Pseudomonas sp. dominated the raw salmon microbiota while in the following days (7 and 10), P. phosphoreum and L. piscium were identified as the main bacterial groups. This study enhances the knowledge of MAP and vacuum-packed raw salmon spoilage microbiota.
► 13 different bacterial taxa were identified by phenotypic and molecular tests. ► A shift of the dominant microflora during storage was brought to light. ► The dominant bacterial populations displayed by PCR–TTGE were identified.
The spoilage potential of six bacterial species isolated from cooked and peeled tropical shrimps (
Brochothrix thermosphacta,
Serratia liquefaciens-like,
Carnobacterium maltaromaticum,
Carnobacterium ...divergens,
Carnobacterium alterfunditum-like and
Vagococcus penaei sp. nov.) was evaluated. The bacteria were inoculated into shrimps, packaged in a modified atmosphere and stored for 27
days at 8
°C. Twice a week, microbial growth, as well as chemical and sensory changes, were monitored during the storage period. The bacteria mainly involved in shrimp spoilage were
B. thermosphacta,
S. liquefaciens-like and
C. maltaromaticum whose main characteristic odours were cheese-sour, cabbage-amine and cheese-sour-butter, respectively. The volatile fraction of the inoculated shrimp samples was analysed by solid-phase microextraction (SPME) and gas chromatography coupled to mass spectrometry (GC–MS). This method showed that the characteristic odours were most likely induced by the production of volatile compounds such as 3-methyl-1-butanal, 2,3-butanedione, 2-methyl-1-butanal, 2,3-heptanedione and trimethylamine.
► Cooked shrimps are very sensitive to microbiological spoilage process. ► Spoilage bacteria can produce chemical compounds with off-flavour. ► Such compounds give rise to a shelf-life decrease of cooked shrimps. ► Spoilage potential of bacteria evaluated using SPME–GC–MS and sensory analysis. ►
B. thermosphacta,
S. liquefaciens,
C. maltaromaticum are the main spoilage bacteria.
The spoilage potential of isolates belonging to five bacterial groups/species (Shewanella baltica, Carnobacterium maltaromaticum, Aeromonas salmonicida, Vibrio sp., “other Gamma-Proteobacteria” ...containing one strain of Pseudoalteromonas sp. and one strain of Psychrobacter sp.) isolated from spoiled cooked and whole tropical shrimp stored under modified atmosphere packaging (MAP) was evaluated by inoculation into ionized cooked and peeled tropical shrimp followed by storage for 32 days at 8 °C. Microbial growth and sensory changes were monitored during the storage period. The major spoilage bacterial isolate groups were C. maltaromaticum and S. baltica. In order to characterize their spoilage potential further and to study the effect of their interactions, each of these two specific spoilage organisms (SSO) and one mixed-culture, C. maltaromaticum/S. baltica, were tested using a combination of complementary methods: molecular (PCR-TTGE), sensory, chemical, and conventional microbiological analyses. It was concluded that, in the mixed-culture-inoculated samples, both species groups imposed their spoilage characteristics.
•Spoilage potential of 5 bacterial groups isolated from spoiled cooked whole shrimp.•Specific spoilage organisms were identified among these bacterial groups.•Characterization of spoilage potential and bacterial interactions of 2 dominant spoilers.•In co-culture, each bacterial group imposed its spoilage characteristics.
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.
•AFLP fingerprinting is a reliable tool for genotyping bacterial isolates.•Diversity of bacterial isolates is shown by AFLP genotyping.•The method allows the species delineation in the P. phosphoreum species group.•Both P. iliopiscarium and P. phosphoreum are present in salmon products.
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