Evolution du potentiel d oxydoréduction dans le lait et au cours de la transformation fromagère (impact des composants intrinsèques et extrinsèques et des bactéries lactiques)

L implication du potentiel rédox (Eh) de la matrice lait à la transformation fromagère jusqu à l affinage a été appréhendée. Une première partie du travail répond à l attente des chercheurs et des industriels qui souhaitent exploiter la mesure du Eh. Une procédure complète d utilisation des électrodes de platine est proposée ainsi qu une méthode de standardisation des résultats afin que ceux-ci puissent être facilement comparables et interprétables. Après la mise en place de la mesure en continu du Eh en fromagerie, l étude de l évolution du Eh au cours d un process type pâte pressée non cuite a permis de mettre en évidence l étape clé où les bactéries lactiques imposent au milieu un Eh réducteur d environ -300 mV, l étape du pressage. Puis au cours de l affinage du Camembert, un gradient rédox a été observé par l utilisation des microélectrodes, lequel évolue au cours de l affinage. Le gradient se situe essentiellement à la surface, la masse fromagère étant principalement réductrice. Dans la seconde partie, l étude du Eh et du pouvoir antioxydant des laits crus, selon l alimentation des bovins, n a pas permis de mettre en évidence des différences. Les acteurs principaux dans l évolution du Eh du lait sont les bactéries lactiques. Plusieurs phases dans la cinétique de réduction ont pu être caractérisées. Dans la dernière partie de l étude, nous avons cherché à comprendre ce qui permettait aux lactocoques d imposer un Eh réducteur au milieu. La technique de filtration en anaérobiose a permis de montrer que ce sont les cellules elles-mêmes et plus précisément leurs propriétés de surface. Cette technique permet de différencier les micro-organismes pour lesquels la valeur du Eh final imposée au milieu est due à une production de molécules et/ou aux cellules elles-mêmes. Nos résultats démontrent le large spectre d action du Eh et l intérêt de l utilisation et du suivi de ce paramètre en industrie laitière.The involvement of the redox potential (Eh) of milk matrix in the cheese transformation has been studied. The first part of this study answers to the expectations of searchers and industrials who want to use the Eh measurement. A full procedure for use of platinum electrode is proposed as well as a method for results standardisation enabling their easy comparison and interpretation. After establishing the continued measure of Eh in dairy, the study of Eh evolution during a type process allowed to highlight the key step in which lactic acid bacteria lead the medium to a reducing Eh of approximately -300 mV, the pressing step. Then, in the Camembert cheese, a redox gradient has been observed using microelectrodes, evolving during the ripening. In the second part, the study of Eh and antioxidant capacity of raw milk, depending on feeding, didn t highlight any difference. In the final part of the study, we searched to understand what mecanisme was used by lactococci to fixe a reducing Eh to the medium. The anaerobic filtration technique shows that it was the cells themselves and more precisely their surface properties. This technique differentiated the microorganisms for which the final Eh value leaded to the medium is due to a molecule synthesis and/or to the cells themselves. Our results demonstrate the large range of action of Eh and the interest to follow up this parameter in the dairy industry.DIJON-BU Sciences Economie (212312102) / SudocSudocFranceF

Compréhension et caractérisation des mécanismes physiologiques impliqués dans l'activité réductrice de Lactococcus Lactis

Parmi les bactéries lactiques, Lactococcus lactis est la plus utilisée en fabrication fromagère. Actuellement, les ferments lactiques sont majoritairement choisis pour leurs propriétés acidifiantes, protéolytiques et aromatiques. Un autre paramètre majeur est le potentiel redox (Eh). En effet, un Eh réducteur est souvent associé à une bonne qualité aromatique. L activité réductrice de L. lactis pourrait donc être un nouveau paramètre à prendre en compte dans la maitrise du Eh dans la fabrication des produits laitiers fermentés. Néanmoins, les mécanismes impliqués dans l activité réductrice de L. lactis demeurent encore inconnus. L objectif de ce présent travail de thèse a été de les découvrir. Tout d abord, nous avons développé des milieux de culture gélosé de discrimination redox utilisant des sels de tétrazolium pour cribler une banque de mutants aléatoires de L. lactis. Ceci a permis de démontrer la participation partielle de la chaine de transport d électrons (Ménaquinones) dans l activité réductrice de L. lactis. Ensuite, l approche biochimique nous a permis de déterminer les composés biochimiques principaux contribuant à la diminution du Eh vers des valeurs très réductrices. La présence de groupements thiols exofaciaux est responsable du Eh réducteur atteint par L. lactis. Enfin, l analyse protéomique utilisant un marquage spécifique des protéines thiols de surface a mis en évidence la présence d une dizaine de protéines exposant des groupements thiols exofaciaux potentiellement impliquées dans l activité réductrice de L. lactis. Les thiols sont connus pour être de très puissants antioxydants ce qui confère à L. lactis un intérêt supplémentaire à prendre en considération dans l élaboration des produits laitiers fermentés.Among the Lactic Acid Bacteria, Lactococcus lactis is the most used in cheese making. Nowadays, starters are used mainly for their acidifying, proteolytic and flavor properties. Another important parameter is the redox potential (Eh). Indeed, reducing Eh is often related to good flavor properties. The reducing activity of L.lactis should be therefore a new parameter to take into account in the monitoring of Eh during dairy fermented products making. Nevertheless, the mechanisms involved in the reducing activity of L.lactis are still unknown. The aim of this work was to understand them. First of all, we have developed tetrazolium salts agar plate media in order to screen a random bank of mutants of L. lactis on their redox capacities. These media allowed us to demonstrate the partial implication of the electron transport chain (Menaquinone) in the reducing activities of L. lactis. Secondly, we have determined the biochemical compounds involved in the decrease of Eh to very reducing values thanks to a biochemical approach. Exofacial thiol groups are mainly responsible for the reducing Eh reached by L.lactis. Lastly, a proteomical analysis using a specific staining of thiols surface proteins revealed the presence of about ten proteins displaying thiols exofacials groups. These proteins might be involved in the reducing activity of L.lactis. Thiols are known to be very strong antioxidants which confer to L. lactis an additional interest to consider in dairy products making.DIJON-BU Doc.électronique (212319901) / SudocSudocFranceF

La fermentation en milieu solide : une innovation de rupture à (re)découvrir

Référence : 201511123537National audienceLe principal challenge de l’industrie des biotechnologies est lié au développement d’un procédé qui est à la fois économique et efficace en utilisant des matières premières renouvelables pour délivrer des produits à haute valeur ajoutée. La fermentation en milieu solide (FMS) qui met en œuvre des microorganismes sur des matières premières biologiques est un procédé pouvant répondre à ces problématiques

Immunomodulatory Properties of Filamentous Fungi Cultivated through Solid-State Fermentation on Rapeseed Meal

International audienceWater extracts from solid-state fermentation (SSF) on rapeseed meal using filamentous fungi exhibit interesting immunomodulatory activities in vitro. Immunomodulation was determined by the capacity of the compounds to activate blood neutrophils and to influence cytokine production in human peripheral blood mononuclear cells (PBMC) and mouse bone marrow-derived macrophages (BMDM). Among the strains tested, Aspergillus sojae mycelium and SSF extracts were the most promising in terms of enhancing the immune response. The filamentous fungus was also successfully cultivated in a pre-pilot bioreactor with forced aeration. The results indicated that the extracts not only activated blood neutrophils but also significantly modulated IL-1β cytokine levels with lipopolysaccharide (LPS)-stimulated PBMC and BMDM without any cytotoxicity in immune cells. IL-1β was down-regulated in a dose-dependent manner in the presence of A. sojae crude mycelium and SSF extract with PBMC, which indicated that there was an anti-inflammatory activity, whereas IL-1β secretion was up-regulated in the presence of stimulated BMDM with the highest concentration that was tested (100 μg/mL). The non-fermented rapeseed had no effect at the same concentration. SSF culture, as a natural product, may be a good source for the development of functional feed with an immunostimulating effect or could potentially be used in medicinal applicat

A novel method to assess heat transfer and impact of relevant physicochemical parameters for the scaling up of solid state fermentation systems

International audienceHeat production during fermentation is undesirable. It can affect the growth of biomass, sporulation, products formation and the scaling-up. Physico-chemical properties of substrates influence heat and mass transfer in Solid State Fermentation. Heat is chemically produced into substrates without micro-organism to allow better reproducibility. A 24-1 fractional factorial design is chosen to study the influence of four physicochemical parameters on heat transfer: Granulometry, Bulk Density, Carr Index (compressibility index) and Water Absorption Capacity. Results show that the two main physicochemical parameters which influence heat transfer are Granulometry and Carr Index. High Granulometry and low Carr Index have influence on maximum temperature reached during the test, warm-up speed and cooling speed. These two parameters allow efficient air flow through the substrate bed with large interparticle spaces enhancing exchange surface between air and particles. A substrate with these characteristics facilitates heat transfers in forced-aerated reactors

Effect of Elevated Oxygen Concentration on the Yeast <i>Yarrowia lipolytica</i> for the Production of γ-Decalactones in Solid State Fermentation

To study the effect of elevated oxygen concentrations on β-oxidation for the production of lactones by Yarrowia lipolytica W29 in solid state fermentation (SSF), experiments using oxygen-enriched air, with different initial concentrations of oxygen ratio, were carried out. Growth kinetics using an oxygen ratio of 30% reached the stationary phase earlier than other conditions used. In addition, the production of γ-decalactone and 3-hydroxy-γ-decalactone reached the maximal concentrations of 270 mg L−1 and 1190 mg L−1, respectively. Using higher initial oxygen ratios (40% and 50%), an incomplete growth inhibition occurred and resulted in a higher concentration of yeast at the stationary phase and a slightly higher 3-hydroxy-γ-decalactone accumulation. When oxygen-enriched air (oxygen ratio of 30%) was injected twice (at 0 and 20 h), 3-hydroxy-γ-decalactone reached a higher concentration (1620 mg L−1) and it reached a very high concentration of 4600 mg L−1 in the condition of oxygen-enriched air injected many times (at 0, 20, 35, 48 and 60 h). This study suggested that oxygen is required for the production of 3-hydroxy-γ-decalactone in SSF. Oxygen may be consumed preferentially for long-chain fatty acid oxidations rather than at C10-level. Furthermore, the production of γ-decalactone may be improved by optimizing the growth conditions to reach a very high specific growth rate. A low oxygen availability in the system at the stationary growth phase led to an inhibition of γ-decalactone degradation. From the present work, an alternative system is proposed as a novel model to study the effect of elevated oxygen concentration in SSF

A New Alternative In Vitro Method for Quantification of Toxoplasma gondii Infectivity

International audienceAn in vitro method to determine the infectious potency of an unknown suspension of the protozoan parasite Toxoplasma gondii based on kinetics of host cells lysis was developed. Mic1-3KO a mutant strain of T. gondii RH tachyzoites was inoculated in 25-cm² flasks containing a 90% confluent monolayer of human foreskin fibroblasts. Lysis kinetics was monitored for infection ratios ranging from 1∶10⁶ to 1∶10; we defined 10⁶ tachyzoites/ml⁻¹ as the threshold value for parasite egress. Results allowed us to build a calibration curve relating the initial infection ratios to the time needed to reach 10⁶ tachyzoites/ml⁻¹. Finally, we validated the method using a known mixture of dead and live parasites. This method was found to estimate with accuracy the initial ratio of infection of the unknown parasite suspension. This easy-to-use method is reproducible and can be applied to any T. gondii tachyzoite RH strain, genetically modified or not. This method is also suitable for testing promising candidates for an effective live vaccine

Eh and pH gradients in Camembert cheese during ripening: Measurements using microelectrodes and correlations with texture

International audienceThis study investigated the use of microelectrodes to continuously and simultaneously monitor pH and redox potential (Eh) gradients in Camembert cheeses from the rind to the core, as a function of ripening time (15 and 35 days). Cheeses were shown to be heterogeneous throughout their mass. An Eh gradient existed from the rind to the core. The surface was oxidizing (+330 to +360 mV) and the core was reducing and became more so in the course of ripening (−300 to −360 mV). A relationship between firmness and Eh was shown. pH gradients were in line with those previously described in the literature and related to ammonium and lactate gradients. Gradients evolved from the rind to the core (pH 7.7 to 5.2 at 15 d and 7.5 to 6.8 at 35 d). These findings showed that both the Eh and pH constituted control parameters for cheese ripening

Solid state fermentation for the production of γ-decalactones by Yarrowia lipolytica

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WITHDRAWN: Dataset on solid state fermentation for the production of lactones by Yarrowia lipolytica

International audienceThe data presented in this article are related to the original article entitled “Solid state fermentation for the production of γ-decalactones by Yarrowia lipolytica” (Try et al. 2008). In this work, the potential of solid state fermentation (SSF) is investigated for the production of γ-lactones with Y. lipolytica W29. The investigation focused on the impact of aeration on metabolites. In that goal, experiments were carried out in three different SSF reactor types, wide-mouth Erlenmeyer flask (static aeration), forced aeration mini-reactor, and small-headspace bottle (without aeration). From the present work, an alternative process is proposed as a novel model for lactone production