Extraction and characterization of soy hull polysaccharide-protein fractions: Analysis of aggregation and surface rheology

Abstract

Soy hull soluble fractions (HSF) were obtained by acid or alkaline/acid extraction. By chemical characterization and Fourier Transform Infrared Spectroscopy we demonstrated that galactomannanproteins and arabinogalactanproteins are solubilized in alkaline or acid medium, while high methoxyl pectic polysaccharides are solubilized in hot acid medium. In this work functional properties of HSF were studied, both in solution and in air-water interfaces. Z-potential versus pH showed that the presence of higher polysaccharide/protein ratios decreases the isoelectric point of soy hull proteins. Turbidimetry and particle size showed that soy hull proteins aggregate at acidic pHs (around the isoelectric point), but this tendency is diminished as the amount of polysaccharide increases. Besides, HSF accumulate at the air-water interface and generate viscoelastic films. Higher viscoelastic parameters are obtained around the isoelectric points, and higher polysaccharide ratios provides higher elasticity at more acidic pHs. We propose that this will improve the protection of the air-water surface at extreme pHs provided by HSF.