Étude qualitative et quantitative des interactions entre la -lactoglobuline et la pectine en système dilué
|Advisor:||Turgeon, Sylvie; Gauthier, Sylvie|
|Abstract:||The aim of this study was to characterize protein/polysaccharide interactions using the β-lactoglobulin (β-lg)/pectin as a model system. The pH values leading to the formation of soluble complexes (pHc) between β-lg and low or high-methoxyl-pectin (LM- or HM-pectin) measured with titration were 6.1 and 5.5, respectively. The destabilizing effect of sodium chloride, urea and temperature has demonstrated that interactions in the systems are mainly caused by electrostatic forces and, to a lesser extent, hydrogen bonding. Binding parameters of β-lg/pectin complexes were determined using frontal analysis continuous capillary electrophoresis (FACCE). At pH 4, approximately 23 β-lg molecules are cooperatively complexed on LM-pectin, where each β-lg molecule covers an average of 12 D-galA residues. The calculated binding constant is 1431 M-1. The peptides β-lg 132-148, 76-83, 41-60, and 1-14 would be involved in the interaction with the pectin. Isothermal titration calorimetry (ITC) was used to characterize the thermodynamic parameters of β-lg/LM- or HM-pectin complexes. The binding isotherms revealed the formation of soluble intrapolymer complexes further followed by their aggregation in insoluble interpolymer complexes. The soluble complexes were enthalpically driven, whereas enthalpic and entropic factors were involved in the insoluble complexes formation. Static light scattering was used to monitor the phase separation of β-lg/LM and HM-pectin mixtures as they were acidified with glucono-δ-lactone (GDL). This technique was used to confirm the two-step mechanism observed with ITC. The phase separation resulting from complexation was achieved through a nucleation and growth mechanism. The increase of complexation in solution with acidification led to a local ordering of systems. Complex formation through acidification was confirmed using phase contrast microscopy. A better understanding of β-lg/pectin interactions was required to achieve research projects using complexes as food ingredients.|
|Document Type:||Thèse de doctorat|
|Open Access Date:||11 April 2018|
|Collection:||Thèses et mémoires|
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