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Auto-assemblage de polysaccharides fonctionnalisés : une étude thermodynamique

Abstract : Polymers in solution can self-assemble to form different types of complexes (coacervates, aggregates, etc.). These objects, in addition to being part of the cellular organization, can be repurposed to encapsulate molecules of interest. However, before being able to use them as such, the understanding of the self-assembly mechanisms is essential to be able to control them and thus form targeted objects. This thesis work focuses on the self-assembly between gum Arabic and chitosan. The interactions involved in associative phase separation are mainly based on electrostatic interactions. Initially, the formation of this complex was analyzed from a thermodynamic point of view by isothermal calorimetric titration, depending on the physicochemical parameters, in particular the pH, the temperature and the molar ratio. It was thus demonstrated that an increase in temperature or pH favored enthalpy and disfavored entropy and that it was possible to form coacervates under all studied conditions by controlling the pH/temperature combination. To change the number and nature of the interactions between polysaccharides, they were modified by enzymatic pathway. A process developed at the laboratory, based on the use of a laccase to oxidize ferulic acid, has been implemented. First, the modification of gum Arabic was demonstrated, in particular with the support of spectroscopic tools (IR-FT, NMR). In addition, the structure of the numerous oxidation products has been studied (NMR, LCMS). The products obtained are mainly ferulic acid dimers and a complete structure has been elucidated. The products grafted on the gum are of phenolic nature so their grafting has an impact on its techno-functional properties (water solubility, thermal and rheological behavior, surface tension, antioxidant properties, etc.). Finally, the grafting of phenolic compounds modified the polysaccharides hydrophobia and charges, so they were mixed in order to determine the impact of these new groups on the interactions involved in the self-assemblies and the nature of the complexes formed. Under given conditions and depending on the polysaccharides used, it is possible to form coacervates, aggregates or even a mixture of both. The formation of these objects was correlated with a study of the thermodynamic parameters involved. These results paves the way for understanding and controlling complexation between polysaccharides that, in the longer term, will lead to applications in the field of encapsulation.
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Submitted on : Thursday, January 13, 2022 - 3:58:02 PM
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Marie E. Vuillemin. Auto-assemblage de polysaccharides fonctionnalisés : une étude thermodynamique. Ingénierie des aliments. Université de Lorraine, 2019. Français. ⟨NNT : 2019LORR0177⟩. ⟨tel-02559619⟩



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