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Structuration de matrices à base de pectine : formulation, caractérisation, fonctionnalités et libération contrôlée lors de l'encapsulation

Abstract : In this thesis, we studied the interactions between an anionic polysaccharide (pectin) and monovalent cation (Na+) and divalent cations (Ca2+, Zn2+, Ba2+, Mg2+) in dilute regime (c < c*) and concentrate regime (c ≈ c *). Thus, a low methoxy pectin (LMP) was studied in comparison with a polygalacturonic acid (PGA). The affinity to bind calcium ions for these polysaccharides decreases as the NaCl concentration increases. This binding affinity was higher for Ca-polyGal than for Ca-LMP due to the low rigidity of chains observed in the polyGal. The interactions between four divalent cations (Ca2+, Zn2+, Ba2+, Mg2+) and the two biopolymers (polyGal and LMP) in the dilute regime were studied in order to obtain information about the network structure, the mode of association and the binding energy. Therefore, we propose a mechanism of the binding which consists of two steps: i) formation of monocomplexations and point-like cross-links ii) formation of dimers. The threshold molar ratio (R* = [M2+]/[Gal]), between these two steps depends on the number and the stability of the point-like cross-links between polyGal chains and the cation. Mg2+ interacts so strongly with water that is remains weakly bound to polyGal (polycondensation) by sharing water molecules from its first coordination shell with the carboxylate groups of polyGal. Molecular dynamic simulations of galacturonate chains in explicit water showed that the « egg-box » model is more adapted for zinc cations than for calcium and barium. When the concentration of the polyGal is close to the overlap concentration (c*), the addition of divalent cations allows to obtain gels for only three cations (Ca2+, Zn2+, Ba2+). The viscoelastic properties of these gels and the gelation kinetics were studied. In the case of gel formation, the first step (formation of monocomplexations and point-like cross-links) is accompanied by an increase in the gel thickness; while the second step (formation of dimers) leads to a densification of the gel. We found that the diffusion coefficient of the gel front increased according the following order: Ba2+ > Ca2+ > Zn2+ > Mg2+; this may be related to the affinity between the water molecules from the coordination sphere and the cation. Indeed, the affinity of the cation for water molecules increases in the reverse order: Ba2+ < Ca2+ < Zn2+ < Mg2+. Finally, we have used the three polysaccharides (PGA, LMP and ALMP - amidated low methoxyl pectin) in association with calcium ions to produce microparticles containing rutin to target drug release in the intestine. We have linked the rutin release kinetics to the network structure established in the gelation step. ALMP microparticles had higher ability to uptake water and thus higher drug release rate than two others microparticles (Ca-LMP and Ca-PGA). The Ca-ALMP gel was more flexible and had the lower viscoelastic modulus than Ca-PGA and Ca-LMP gels. We attributed this to the random distribution of ester and/or amide groups in ALMP, which hinders the formation of dimers: the hydrogen bonds between the amine groups and carboxylate groups are responsible for the flexibility of the network formed.
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Thi Diem Uyen Huynh. Structuration de matrices à base de pectine : formulation, caractérisation, fonctionnalités et libération contrôlée lors de l'encapsulation. Ingénierie des aliments. Université de Bourgogne, 2016. Français. ⟨NNT : 2016DIJOS019⟩. ⟨tel-01508191⟩



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