Development of an SPME-GC-MS method for the specific quantification of dimethylamine and trimethylamine: use of a new ratio for the freshness monitoring of cod fillets

International audienceBACKGROUND: Fish is a highly perishable food, so it is important to be able to estimate its freshness to ensure optimum quality for consumers. The present study describes the development of an SPME‐GC‐MS technique capable of quantifying both trimethylamine (TMA) and dimethylamine (DMA), components of what has been defined as partial volatile basic nitrogen (PVB‐N). This method was used, together with other reference methods, to monitor the storage of cod fillets (Gadus morhua) conserved under melting ice.RESULTS: Careful optimisation enabled definition of the best parameters for extracting and separating targeted amines and an internal standard. The study of cod spoilage by sensory analysis and TVB‐N assay led to the conclusion that the shelf‐life of cod fillet was between 6 and 7 days. Throughout the study, TMA and DMA were specifically quantified by SPME‐GC‐MS; the first was found to be highly correlated with the values returned by steam distillation assays. Neither TMA‐N nor DMA‐N were able to successfully characterise the decrease in early freshness, unlike dimethylamine/trimethylamine ratio (DTR), whose evolution is closely related to the results of sensory analysis until the stage where fillets need to be rejected.CONCLUSION: DTR was proposed as a reliable indicator for the early decrease of freshness until fish rejection

Rapid multiparameters approach to differentiate fresh skinless sea bass (<em>Dicentrarchus labrax</em>) Fillets from frozen-thawed ones

International audienceFood authenticity is one of the major issues in the mind of today's consumers. The sale of frozen-thawed fish fillets under the "fresh fillet" label is considered as a commercial fraud. However, their close sensory properties complicate the differentiation. This study focused on analyzing the composition of exudate (pressured flesh juice) in order to rapidly differentiate between fresh and frozen-thawed skinless fillets of sea bass (Dicentrarchus labrax). Protein concentration, alpha-D-glucosidase specific activity, nucleotides and related compounds (NRCs) concentration, and free calcium concentration were measured in exudates corresponding to fresh or frozen-thawed sea bass fillets. Significant increases of these four parameters were observed in exudates from frozen-thawed fillets, especially with a twofold increase in NRCs and free calcium concentrations. These results suggest that NRCs and free calcium concentrations can be promising indicators to rapidly detect mislabeling of fresh fillets

Differentiating between fresh and frozen-thawed fish fillets by muscle fibre permeability measurement

International audienceThere is no comprehensive method for differentiating between fresh and frozen-thawed fish fillets. This is an ongoing problem, particularly in relation to regulations. In this study, we showed the relevance of using the properties of mitochondria to discriminate fresh fish fillets from frozen-thawed fish fillets. The use of red muscle fibres of Gilthead sea bream allowed us to leave mitochondria in their physiological environment and to avoid possible alterations of mitochondrial membranes during isolation steps. The impact of freezing on fillets was evaluated by measuring the permeability of fibres and mitochondrial membranes to nicotinamide adenine dinucleotide + hydrogen (NADH). NADH permeability of fresh fillet fibres stored at 4°C was compared to the permeability of fibres extracted from frozen-thawed fillets. Two approaches were used to measure permeability changes: a spectrophotometric method that measured consumption of NADH by complex I, and an oxygraphic approach that measured stimulation of O 2 consumption by NADH. Fibres from frozen-thawed fillets were more permeable to NADH and were less sensitive to the permeabilizer alamethicin. The 2 sensitivity of this method allowed us to clearly detect red muscle fibres from frozen-thawed fish versus fresh fish fillets

Differentiating between fresh and frozen-thawed fish fillets by muscle fibre permeability measurement

International audienceThere is no comprehensive method for differentiating between fresh and frozen-thawed fish fillets. This is an ongoing problem, particularly in relation to regulations. In this study, we showed the relevance of using the properties of mitochondria to discriminate fresh fish fillets from frozen-thawed fish fillets. The use of red muscle fibres of Gilthead sea bream allowed us to leave mitochondria in their physiological environment and to avoid possible alterations of mitochondrial membranes during isolation steps. The impact of freezing on fillets was evaluated by measuring the permeability of fibres and mitochondrial membranes to nicotinamide adenine dinucleotide + hydrogen (NADH). NADH permeability of fresh fillet fibres stored at 4°C was compared to the permeability of fibres extracted from frozen-thawed fillets. Two approaches were used to measure permeability changes: a spectrophotometric method that measured consumption of NADH by complex I, and an oxygraphic approach that measured stimulation of O 2 consumption by NADH. Fibres from frozen-thawed fillets were more permeable to NADH and were less sensitive to the permeabilizer alamethicin. The 2 sensitivity of this method allowed us to clearly detect red muscle fibres from frozen-thawed fish versus fresh fish fillets

Quantification of organic plastic additives in plastics with (TD) Py-GC-HRMS

International audiencePlastics were revolutionary inventions that symbolized globalization and the interconnection of economies between countries in the second half of the 20th and the early of the 21st centuries. They are widely used in various industrial sectors including food packaging, construction, automotive, electronics, textiles, household items, and toys, with the current global production reaching over 370 million tons per year. These synthetic materials are made of an organic polymer matrix and chemical additives. In total, more than 10 000 additives were identified in plastics and over 2 400 are considered as substances of potential concern as they meet one or more of toxicity criteria in the European Union (toxicity for reproduction, bioaccumulation,…).These substances may leached during the plastic life cycle (to foodstuff, environment, etc), resulting in potential human exposure.Thus, the development of analytical methods capable of identifying and quantifying additives in plastics is necessary. It has been demonstrated that the thermal desorption method using aPyrolysis coupled to GC-HRMS system can be a useful analytical tool for the rapid quantification of additives in polymer samples but method still need to be developed. For this study, additives of interest were first selected based on two main criteria: their toxicity according to the European Chemicals Agency and their migration limits set by EU Regulation No 10/2011. In total, 13 additives were selected (5 plasticizers, 6 flame retardants and 2 UV stabilizers).Then, a reflection was set up in order to consider how to evaluate the response function of additives in the context of solid-state sample direct analysis. It was chosen to develop reference material incorporating additives into a polymer matrix at specified concentration levels, to produce plastic films, using masterbatch. This process is aimed to ensure homogeneous dispersion of the additives in the polymer matrix.Finally, some preliminary analytical developments were carried out in order to perform future analyses, like acquisition of additives HRMS spectra, MS/MS patterns to select the optimum collision energies for each characteristic ion and the most abundant fragment resulting from fragmentation. A first application on solid-state plastic will be proposed

Structural characterization of the extracellular polysaccharide from Vibrio cholerae O1 El-Tor

The ability to form biofilms is important for environmental survival, transmission, and infectivity of Vibrio cholerae, the causative agent of cholera in humans. To form biofilms, V. cholerae produces an extracellular matrix composed of proteins, nucleic acids and a glycoconjugate, termed Vibrio exopolysaccharide (VPS). Here, we present the data on isolation and characterization of the polysaccharide part of the VPS (VPS-PS), which has the following structure: -4)-\u3b1-GulpNAcAGly3OAc-(1-4)-\u3b2-D-Glcp-(1-4)- \u3b1-Glcp-(1-4)-\u3b1-D-Galp-(1- where \u3b1-D-Glc is partially ( 3c20%) replaced with \u3b1-D-GlcNAc. \u3b1-GulNAcAGly is an amide between 2-acetamido-2-deoxy-\u3b1-guluronic acid and glycine. Apparently, the polysaccharide is bound to a yet unidentified component, which gives it high viscosity and completely suppresses any NMR signals belonging to the sugar chains of the VPS. The only reliable method to remove this component at present is a treatment of the whole glycoconjugate with concentrated hydrochloric acid.Peer reviewed: YesNRC publication: Ye

Structural studies of the rhamnose-rich cell wall polysaccharide of Lactobacillus casei BL23

Lactobacillus casei is a Gram positive lactic acid bacterium used in dairy fermentations and present in the normal human gut microbiota. Certain strains are recognized as probiotics with beneficial effects on human and animal health. L. casei BL23 is a potential probiotic strain endowed with anti-inflammatory properties and a model strain widely used in genetic, physiological and biochemical studies. A number of bacterial cell surface polysaccharides have been shown to play a role in the immune modulation activities observed for probiotic lactic acid bacteria. In the present work, we purified the most abundant carbohydrate polymer of L. casei BL23 cell wall, a neutral wall polysaccharide (WPS) and established its chemical structure by periodate oxidation, methylation analysis and 2D NMR spectroscopy. The WPS of L. casei BL23 was shown to contain alpha-Rha, alpha-Glc, beta-G1cNAc and beta-GaINAc forming a branched heptasaccharide repeating unit (variant 1) with an additional partial substitution with alpha-Glc (variant 2). A modified non-reducing end octasaccharide, corresponding to a terminal unit of the WPS (variant 3), was also identified and allowed to define the biological repeating unit of the WPS. To our knowledge, this is the first report of the identification of a biological repeating unit based on a chemical evidence, in a cell wall polysaccharide of a Gram positive bacterial species

Differentiating between fresh and frozen-thawed fish fillets by mitochondrial permeability measurement

International audienceIn this study, we investigated the properties of mitochondria to discriminate fresh from frozen-thawed fish fillets. Mitochondria were isolated from gilthead seabream fillets and the impact of freezing was evaluated by measuring the permeability of mitochondrial membranes. Freezing led to permeabilization of mitochondrial inner membranes to reduced nicotinamide adenine dinucleotide (NADH). The increase in permeability related to freezing shock was compared to the physiological permeabilization of mitochondria isolated from gilthead seabream fillets stored at 4°C. Two approaches were chosen to measure the increase in permeability: a spectrophotometric method to measure the consumption of NADH by complex I, and an oxygraphic method to measure O2 consumption by respiratory chains after exposure of mitochondria to NADH. Mitochondria isolated from frozen-thawed fillets were highly permeable to NADH and were no longer sensitive to a membrane permeabilizing agent: alamethicin. Altogether, our scientific approach allowed us to discriminate mitochondria isolated from fillets that have been exposed or not to a freezing shock (-80°C) and thus to discriminate between fresh and frozen-thawed fish fillets

Study of a fishery product process in the frame of microplastics research

International audienc