Elaboration de céramiques nanostructurées en carbure de silicium (de la synthèse de la poudre à la céramique frittée)

Les matériaux des réacteurs nucléaires du futur seront soumis à des températures et des flux de neutrons très élevés. Il est alors envisagé d utiliser des matériaux céramiques tels que le carbure de silicium sous la forme de composite SiCf/SiC nanostructuré. Il est cependant encore nécessaire de vérifier l apport de la nanostructuration sur le comportement de ce matériau sous irradiations. Afin de vérifier la faisabilité et déterminer les propriétés de la matrice, il a été envisagé de fabriquer celle-ci seule par métallurgie des poudres à partir de nanoparticules de SiC. L objectif est d obtenir du SiC dense et nanostructuré sans avoir recours à des ajouts de frittage. Pour cela, une étude paramétrique de la phase de synthèse et de densification a été réalisée dans l objectif de mieux connaître l influence des paramètres clés et les mécanismes mis en jeu. Ainsi l étude de la synthèse des nanopoudres par pyrolyse laser a permis de produire, avec des taux de production élevés, des lots de nanoparticules de SiC homogènes dont la taille peut être ajustée entre 15 et 90 nm. Ces poudres ont été densifiées par une méthode innovante : le Spark Plasma Sintering (SPS). L étude puis l optimisation des paramètres clés ont permis de densifier, sans avoir recours à des ajouts, du SiC (3.1 g/cm3) tout en conservant la nanostructuration du matériau. Les matériaux obtenus ont été caractérisés thermiquement et mécaniquement afin de déterminer l influence de la nanostructuration sur leur comportement.The materials used inside future nuclear reactors will be subjected to very high temperature and neutron flux. Silicon carbide, in the form of SiCf/SiC nanostructured composite is potentially interesting for this type of application. It is again necessary to verify the contribution of nanostructure on the behaviour of this material under irradiation. To verify the feasibility and determine the properties of the matrix, it was envisaged to produce it alone by powder metallurgy from SiC nanoparticles. The objective is to obtain nanostructured SiC ceramic fully densified and without using sintering aids. For that, a parametric study of the phase of synthesis and agglomeration was carried out, with for objective the determining the active mechanisms and the influence of the key parameters. Thus, the study of the nanopowder synthesis by laser pyrolysis made it possible to produce, with high production rates, homogeneous batches of SiC nanoparticles whose size can be adjusted between 15 and 90 nm. These powders were densified by an innovating method: Spark Plasma Sintering (SPS). The study and the optimization of the key parameters allowed the densification of silicon carbide ceramic without sintering aids while preserving the nanostructure of material. The thermal and mechanical properties of final materials were studied in order to determine the influence of microstructure on their properties.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Kinetics of gluten protein-insolubilisation during pasta processing: decoupling between time- and temperature-dependent effects.

Durum wheat gluten proteins are essential for pasta quality. Glutenin polymers undergo solubilization mechanisms during pasta processing. This study aims to investigate gluten proteins insolubilisation kinetics during a resting period applied to extruded. The goal is to investigate the contribution of time related recovery of large glutenin polymers and temperature related formation of glutenin cross-linked aggregates in the pasta quality. Extruded pasta were rested for 120 minutes at 20, 30 or 40°C prior drying at high temperature (90°C). Glutenins insolubilisation induced by resting and drying was assessed from the SE-HPLC elution profiles of the SDS-soluble proteins from fresh, rested and dried pasta. Final pasta were characterized for their organoleptic (color, surface roughness) and physical (diameter, cooking time, viscoelasticity index) properties, before and after cooking. Pasta quality is discussed in relation with the gluten network structure and the impact of resting time. Resting of freshly extruded pasta extrusion leads to spontaneous insolubilisations of glutenins by creation of weak interactions. High temperature drying induces a strong drop of solubility of all gluten protein fractions by creation of covalent bonds, impacting equally rested and not rested pasta. Dry and cooked pasta organoleptic and physical properties are not significantly impacted by a resting time

Optimization of the oxidative stability and lipid profile of omega-3 enriched infant flours

International audienceDietary diversification, which starts between 4 and 6 months, is a pivotal period in the infant development. Complementary foods such as infant flours are gradually introduced into the infant diet and are widely consumed especially in southern countries. However, infant flours have often an unbalanced lipid profile in favor of omega 6 and overages in certain vitamins content (especially A and E). The aim of this study was to optimize the formulation of vitamin A and E-fortified infant flours in order to improve its nutritional profile and oxidative stability. For this purpose, model infant flours were formulated by optimizing the lipid profile through the inclusion of flours with balanced omega 6/omega 3 ratios, i.e. teff and cowpea flours, and/or by adding long-chain polyunsaturated fatty acids (LC-PUFA) powders. In order to limit their sensitivity to oxidation, two strategies were studied, namely the addition of amaranth leaf powder for their carotenoid content and brown rice peripheral tissues for their phenolic compounds composition. These model infant flours were submitted to storage test during 6 months at 25 or 40°C. As expected the inclusion of LC-PUFA significantly increased the oxidation sensitivity of the flours. The use of raw materials with balanced fatty acid profiles resulted in contrasted omega 6/omega 3 ratio of 6.7 in un-enriched in LC-PUFA model infant flours versus 3.9 for the LC-PUFA enriched model infant flours. As expected, the addition of LC-PUFA increased the sensitivity to oxidation with a significantly higher increase of peroxide value for the flours enriched with these fatty acids. Despite a significant increase of peroxide value, the fatty acid profiles and vitamin E contents remained stable after 1 month of storage. A significant degradation of vitamin A was however observed mainly on short time with up to 50% of retinyl acetate degraded after 2 weeks of storage. This degradation was significantly delayed for model infant flours enriched with amaranth leaf or black rice peripheral tissue. In conclusion optimized omega 3 enriched infant flours could be proposed with fair stability over 3 months of storage

Alternative process of oleic sunflower or rapeseed oleosomes extraction including dry fractionation steps do not lead to chemical, enzymatic nor microbiological deterioration of lipoproteic objects

International audiencePlant lipoproteic assemblies, such as oil bodies (OB), are very interesting vectors of PUFAs. To extract them, classical processes starts with hydration steps and subsequent aqueous crushing possibly followed by a high pressure homogenization step to help breaking up plant tissue and release OB efficiently.Besides this efficient wet integrated process, one can wonder whether some dry fractionation steps (dehulling, grinding, cryogrinding) can help reducing water and energy consumption while allowing acceptable OB extraction. To answer this question, selected dry fractionation operations were applied on two oleoproteagineous seeds (high oleic sunflower, and rapeseed),followed by an aqueous extraction of OB. Seeds and OB emulsions were characterized in terms of microbial load, lipid content, fatty acid profile, lipid classes, peroxide value and tocopherol content. In addition, the particle size distribution and morphology of the OB emulsions were assessed.Seed dehulling by abrasion or by impact is an interesting operation to lower phenolic compounds and fibers in the co-products obtained besides OB. Cryo- or ambient grinding with a ball mill induced efficient particle size reduction even for short treatments (≤30 s) and did not trigger lipolysis, increase of microbial load nor tocopherol oxidation in the seed crush. Such an upstream dry fractionation operation however induced coalescence of part of the OB, yet lead to acceptable recovery of OB (40 % to 60 % of initial lipid content) with preserved fatty acid and tocopherol profiles.This result is part of the OBEINN project which aims at efficient extraction OB for food innovation and should help consolidating sustainable processes of extraction of O

Phenolic composition and kafirin digestibility of Sorghum bicolor is impacted by food processing and by germination

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ECOPHYTO R&D : Vers des systèmes de culture économes en produits phytosanitaires. Volet 2 TOME IX : Conception d'un réseau d'acquisition de références et d'un réseau d'information

International audienceLes pouvoirs publics souhaitent favoriser l’adoption de systèmes de culture économes en pesticides, en mettant en place un réseau d’acquisition de références expérimentales et de démonstration, associé à un système d’information. Pour répondre à cette demande, le groupe "Réseau" a fait un état des lieux, proposé une configuration, et évalué les moyens nécessaires. L’inventaire des dispositifs expérimentaux étudiant des systèmes de culture a recensé 87 dispositifs en grande culture, 33 en arboriculture fruitière, 9 en vigne et 36 en cultures légumières. Les données collectées s’avèrent dispersées et disparates, difficiles à mobiliser et à valoriser faute d’outils compatibles entre eux ou communs pour gérer ces données, et globalement insuffisantes. Le dispositif proposé comprend 2 fonctions complémentaires et indissociables : - un réseau expérimental pour l’acquisition de références, avec la construction et l’évaluation de systèmes de culture économes en pesticides via un réseau d’expérimentation-démonstration comprenant des dispositifs d’apprentissage, de mise en oeuvre en conditions commerciales et de démonstration, avec 3 modules (EXPE, FERME et DECI) ; - un système d’information pour la gestion des connaissances, avec la mise à disposition de ressources pour l’activité des conseillers et la valorisation de l’activité de recherche, d’expérimentation et de production de références, avec 2 modules (BASE et GECO). L’organisation de l’ensemble repose sur un pilotage du dispositif au sein d’un même groupement et un conventionnement avec les partenaires régionaux ou nationaux. En régime de croisière, l’opération pourrait comprendre 50 sites expérimentaux (EXPE), 800 fermes pilotes (FERME), 30 projets de recherche en cours (DECI) sur la base de 10 nouveaux projets d’une durée de 3 ans chaque année, plus la gestion de la base de données et de la plateforme informatique associée (BASE), et la base de gestion des connaissances (GECO). Sur cette base de calcul, il mobiliserait l’équivalent de 130 ETP au total