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Influence de l'état protéique sur la dynamique de séparation de phase et de gélification dans un système ternaire aqueux à base de protéines de pois et d'alginate

Abstract : Two aqueous systems at 20°C in 0.1 M NaCl and pH 7.2 containing globular pea proteins and sodium alginate were investigated in this study. First, phase behavior of (i) either low-denatured mixed globulins or (ii) their thermally pre-aggregated counterparts - alginate mixtures was compared using a multi-scale approach, by means of phase diagram and microstructure analysis by confocal microscopy. Thermodynamic incompatibility was the main driving force leading to phase separation within the mixtures, which presented according to their initial biopolymer composition both different morphological and time-evolution features of coexisting phases. Thereafter, a cold-set gelation for each system was performed, as the slow hydrolysis of glucono-δ-lactone (GDL) acidified the media and mediated the release in situ of calcium ions from calcium carbonate, practically insoluble at pH higher than 7. Such procedure would allow gelation via calcium of alginate only or both alginate and the protein phase, giving rise to filled and mixed gels, respectively. An attempt to correlate rheological measurements (G’, G’’ dynamic moduli) with microstructural data was carried out according to image texture analysis by the cooccurrence method. Phase separation was kinetically entrapped by gelation. Compared to single-alginate gels or native globulins-alginate filled gels where alginate was the only gelling agent via calcium, mixed gels reflected in fact great synergism effect regarding final gel elasticity. Meanwhile, pre-aggregated pea globulins could not form a gel with the gelation procedure of choice here. Besides, stronger segregative effects were evidenced by increasing initial biopolymer composition thus enhancing self-biopolymer interaction in their respective enriched-coexisting phases. The strongest mixed gels displayed entangled structure. According to a differential labelling of each incompatible biopolymer, observations with transmission electron microscopy suggested inter-biopolymer attractive interaction at the interface of coexisting phases, probably via calcium cations. Salt-bridging would reinforce cohesiveness between both protein and alginate networks
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Jean-Luc Mession. Influence de l'état protéique sur la dynamique de séparation de phase et de gélification dans un système ternaire aqueux à base de protéines de pois et d'alginate. Autre. Université de Bourgogne, 2012. Français. ⟨NNT : 2012DIJOS030⟩. ⟨tel-00825480⟩

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