Abstract
Adsorption of Acacia gums (GA) (A. senegal and A. seyal) and A. senegal molecular fractions, made ofarabinogalactan-proteins (AGPs) with different molecular weights, onto latex particles, with different sizes andsurface charges, was studied using molecular (fluorescence and nanoIR spectroscopies, microscopies includingAtomic Force Microscopy) and mesoscopic (Dynamic Light Scattering, zeta potential, Asymmetrical flow field-flow fractionation) methods. Adsorption of GA onto latex particles revealed a complex mechanism of adsorp-tion where the highest adsorption was observed when A. senegal and latex particles were negatively charged. Theinvert was observed for A. seyal where the maximum of adsorption was observed when gum and latex wereoppositely charged. The duality of positive and negative charges on GA macromolecules together with confor-mational changes certainly explain the complex mechanism of adsorption. A mechanism where either the proteinmoiety either the sugars blocks adsorb is to be preferred. This mechanism seems to produce differences ofbehaviour due to viscoelastic properties of adsorbed layers, and differences of hydration due to differences ofpolarity of AGPs. The consequence of electrostatics in the adsorption process is a water release from the adsorbedlayers and important gain in entropy. A fair agreement was found between protein content and adsorbed layerthickness of GA, with the formation of partial coverage, monolayer and multilayer films depending on GAconcentration. Structural changes induced by GA adsorption onto latex particles was probed using fluorescenceand nanoIR spectroscopies without giving clear evidence of conformational changes induced after GA adsorption.The results of this study highlighted that GA surface adsorption process depend not only on the protein moietyand electrostatic interactions but also on other parameters related to AGP hydration status. The protein structuralaccessibility, the molecular weight distribution, the AGPs intrinsic viscoelastic properties allowing structuralrearrangements on the surface and spreading in order to form a viscoelastic film onto latex particles should alsoplay a pivotal role in the adsorption process.