Microbial degradation of seafood

This chapter provides information on the microflora of living fish, contamination and bacterial growth during storage, specific spoilage microorganism concept, bacterial metabolism, spoilage of fresh fish and shelfish depending on storage conditions and spoilage of lightly preserved seafood product such as cold smoked salmon and cooked shrimp packed under modified atmosphere.Ce chapitre décrit la flore bactérienne du poisson vivant, la contamination et la croissance dans la chair durant la conservation, le concept de flore d'altération, le métabolisme bactérien, l'altération des poissons frais et des coquillages selon leur conditionnement et enfin l'altération des produits semi- transformés comme le saumon fumé et les crevettes cuites emballées sous atmosphère modifiée

Détection de la flore d'altération du poisson réfrigéré : évaluation d'un milieu de culture

The study submitted in this paper intendent to assess the ability of a culture medium for the detection and counting of chilled fish spoilage flora. Some authors used a medium allowing the detection of the whole spoilage bacteria on the basis of H2S production but this medium as been only used for cod flora analysis (Gadus morhua) coming from north sea or baltic sea. Therefore this study aimed to assess the efficiency of medium on withing flesh (Merlangius merlangus), gadidae of temperate sea water, on the one hand and salmon flesh (Salmo salar), aquacultural salmonidae, on the other hand. During this study, about 120 bacterial strains (half of them being H2S producing) were isolat respectively from whiting and salmon flesh stored in air or under vacuum. These strains were characterised on the basis of some morphological and biochimical tests. The identifiaction of a few strains with the API 20 NE system was attempted.L'étude présentée dans ce rapport avait pour objet d'évaluer l'aptitude d'un milieu de culture à la détection et au dénombrement de la flore d'altération du poisson réfrigéré. Certains auteurs avaient déjà proposé un milieu de culture permettant la détection de l'ensemble des bactéries de l'altération à partir de la production d'H2S, mais ce milieu n'avait été utilisé que pour l'analyse de la flore du cabillaud (Gadus morhua) de mer du nord et de la baltique. Cette étude avait donc pour but d'évaluer l'efficacité du milieu, d'une part sur de la chair de merlan (Merlangius merlangus), galidé de mer tempérée, et d'autre part sur du saumon (Salmo salar), salmonidé d'aquaculture. Au cours de ce travail, environ 120 souches bactériennes, dont 60 souches productrices d'H2S, ont été isolées respectivement à partir de chair de merlan et de saumon entreposée sous air ou sous vide. Ces souches ont été ensuite caractérisées sur la base de quelques tests morphologiques et biochimiques. Une tentative d'identification sur galeries API 20 NE a été entreprise sur un petit nomGbre d'entre elles

Salt and smoke simultaneously affect chemical and sensory quality of cold-smoked salmon during 5 degrees C storage predicted using factorial design

Simultaneous effect of salt and smoke on chemical indices of cold-smoked salmon and on its shelf life, estimated by sensory analysis, was investigated during vacuum-packed storage at 5 degrees C. Salting salmon immediately decreased the pn in the flesh, probably due to the increase of the ionic force, then pH remained constant during storage. Total volatile base nitrogen and trimethylamine productions were mainly inhibited by the salt concentration in the flesh, whereas phenol had no effect. A highly synergistic effect between the two factors was observed on the shelf life response. When a high level of salt (5% wt/wt) or phenol (1 mg 100 g(-1)) was added separately, shelf life did not exceed 1 week, whereas it could reach more than 10 weeks when salt and smoke were added simultaneously. Different combinations were examined for shelf life characteristics of the product. For instance, 2 and 3% (wt/wt) of salt with, respectively, 0.80 and 0.45 mg 100 g(-1) of phenol were sufficient for a 4-week shelf life, satisfying most of French cold-smoked salmon producers and consumers. Correlation between microbiological responses measured in a previous study and chemical and sensory data were also established

Effect of salt and smoke on the microbiological quality of cold-smoked salmon during storage at 5 degrees C as estimated by the factorial design method

The simultaneous effect of salt and smoke on the natural flora of cold-smoked salmon was studied during 5 weeks of vacuum storage at 5 degrees C. The quadratic polynomial, as a function of factors, was used to express total viable count (TVC), total lactic acid bacteria, lactobacilli numerated on Rogosa agar, H2S-producing bacteria, and yeasts at different sampling times. TVC and total lactic acid bacteria were mainly inhibited by the salt concentration (5% wt/wt) in the meat and to a lesser extent by the phenol content. Inhibition was linearly proportional to salt: and smoke content (the higher the concentration, the greater the inhibition). No synergistic effect on inhibition was observed between the two factors. In our working conditions, the TVC French standard (<10(6) CFU g(-1)) was maintained during 4 weeks of storage at 5 degrees C, with a minimum concentration of 2.4% (wt/wt) of salt in meat and smoking treatment corresponding to 0.6 mg 100 g(-1) of phenol. When the salt level was higher than 3%, the TVC standard was maintained, regardless of phenol level. A negative interaction between the two factors was found for H2S-producing bacteria and a positive one for yeasts

Caractérisation moléculaire de l'écosystème microbien complexe de la crevette cuite et étude des flores d'altération

Les crevettes décortiquées cuites sont des denrées considérées comme fragiles d un point de vue microbiologique, et sensibles au processus d altération organoleptique provoqué par le développement de certaines bactéries. Dans le but de mieux maîtriser leur conservation, la caractérisation de l écosystème microbien de ces produits a été réalisée par le biais d une approche polyphasique, combinant des techniques dites culture-dépendantes, qui permettent l identification phénotypique et moléculaire d isolats bactériens, et des méthodes culture-indépendantes avec la PCR-TTGE et la DHPLC, qui génèrent des empreintes génétiques à partir d un mélange d ADN bactérien extrait directement de la matrice crevette. Cette approche a permis de mettre en évidence les principaux genres et espèces de bactéries présents dans la microflore d altération des crevettes décortiquées cuites. Les bactéries lactiques constituaient le groupe bactérien majoritaire avec les principaux genres : Carnobacterium, Vagococcus, Enterococcus. Au sein du genre Vagococcus, une étude de taxonomie plus approfondie a permis de mettre en évidence la nouvelle espèce Vagococcus penaei .sp .nov. Deux autres groupes bactériens importants étaient retrouvés dans cet écosystème : Brochothrix thermosphacta et Serratia liquefaciens-like. Le potentiel d altération de ces bactéries a été étudié en mettant en œuvre des techniques d analyse sensorielle et d analyse des composés volatils produits par ces bactéries, comme la GC-MS. Trois espèces bactériennes se sont révélées les plus actives dans l altération de ce type de produit : Bt. thermosphacta, St. liquefaciens-like et Cb. maltaromaticumCooked and peeled shrimps are considered as fragile foodstuffs from a microbiological point of view and sensitive to the organoleptic spoilage process induced by the growth of certain bacteria. For a better control of their shelf life, the microbial ecosystem characterisation of this product was carried out by a polyphasic approach combining culture-dependent methods, which allow the phenotypical and molecular identification of bacterial isolates, and culture-independent methods with the PCR-TTGE and DHPLC techniques which generate genetic fingerprintings from a bacterial DNA mixture directly extracted from cooked shrimps matrix. This approach has allowed to highlight the main bacterial genus and species present in the spoilage microbiota of cooked and peeled shrimps. Lactic acid bacteria was the major group with the main genus: Carnobacterium, Vagococcus, Enterococcus. Within the Vagococus genus, a more detailed taxonomic study allowed to discover the novel species Vagococcus penaei .sp .nov. Two other important bacterial groups were found in the shrimp ecosystem: Brochothrix thermosphacta and Serratia liquefaciens-like. The spoilage potential of these bacteria has been investigated by using sensory analysis methods and biochemical techniques to determine the volatile compounds produced by these bacteria, like the gas chromatography coupled to mass spectrometry device. Three species were considered as the most spoiling bacteria in this type of product: Bt. thermosphacta, St. liquefaciens-like and Cb. maltaromaticum.NANTES-BU Sciences (441092104) / SudocSudocFranceF

Antimicrobial and antioxidant activities of cactus polyphenols extract on seafood preservation

The present work investigated the antimicrobial and antioxidant activities of polyphenols extracted from cactus (Opuntia ficus indica) fruit-peels on sardine fillets during refrigerated storage. Biochemical, microbiological and sensorial indicators of treated sardine fillets; were studied comparatively to control lot. Microbial communities were characterized using phenotyping and molecular identification of bacterial isolates; and culture-independent method (PCR-TTGE) for fingerprinting of bacterial DNA extracted from fillets. A principal component analysis (PCA) of all the studied descriptors and variables revealed that discrimination along first principal component (PC1) was mainly correlated positively with peroxidation level and storage time but negatively with polyphenol treatment while along second component (PC2) it was mainly positively correlated to polyphenols treatment and polyene index; confirming the effect of treatment on preservation of sardine fillets. Sensory data studied by the correspondence factorial analysis (CFA) revealed that the addition polyphenols extract extended the shelf life of sardines without altering their sensorial properties. Cactus fruit-peels appeared a promising source of natural bio-preservative agent for aquatic food processing

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 Photobacterium 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

Selection of bioprotective cultures for preventing cold-smoked salmon spoilage

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

Quality assessment of ice-stored tropical yellowfin tuna (Thunnus albacares) and influence of vacuum and modified atmosphere packaging

Metagenomic, microbial, chemical and sensory analyses of Thunnus albacares from Martinique and 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