Characterization and functional properties of soybean high-molecular-mass polysaccharide complex

Soybean soluble polysaccharide (SSPS), extracted from the by-product obtained during isolation of soybean protein, is an anionic polysaccharide that stabilizes milk proteins under acidic conditions. We developed a high-molecular-mass complex of SSPS cross-linked via phosphate (SSPS-HC; absolute molecular weight 2850 kg/mol, radius of gyration 106 nm), and found that it has different protein stabilization properties when compared with the original SSPS (absolute molecular weight 550 kg/mol, radius of gyration 36 nm). The objective of this work was not only to study the rheological properties of SSPS-HC, but also clarify its protein-stabilizing properties in comparison with SSPS; if molecular mass or negative charge affected protein dispersion. Irrespective of high-molecular-mass, SSPS-HC possessed similar rheological properties to SSPS such as low viscosity in aqueous solution. The absolute negative charges of SSPS-HC measured by a zeta potential analyzer at pH range of 2.0-7.0 were higher than those of SSPS. Acidified milk drinks prepared with 8.4% non-fat milk solids and 0.4% SSPS-HC or SSPS showed low viscosity and small protein particle size, and did not aggregate for 14 days. The thickness of the hydrated layer, which was formed on the surface of protein particles by SSPS molecules measured after hemicellulase treatment with DLS (dynamic light scattering), was estimated to be about 89 nm for SSPS-HC and 33 nm for SSPS. These numerical values were in good relation to the molecular diameter of SSPS-HC and SSPS in aqueous solution measured by DLS and AFM image, and suggested that protein particles were dispersed and the hydrated monolayer made on the surface of protein particles by SSPS-HC or SSPS molecules prevented aggregation. However, stabilizing pH ranges were different with stability of SSPS-HC at pH range of 4.0-4.8 and stability for SSPS at pH range of 3.6-4.2. In addition to the difference in the molecular mass and absolute negative charge, the phosphate groups of SSPS-HC were possibly influenced on the protein-dispersing property approximately at isoelectric point of milk protein; SSPS-HC prevent aggregation of casein by accelerating solubility of calcium phosphate under acidic conditions as is already reported in the starches phosphorylated. Crown Copyright (C) 2012 Published by Elsevier Ltd. All rights reserved.