Stabilization of milk protein dispersion by soybean soluble polysaccharide under acidic pH conditions

There are 2 types of soybean soluble polysaccharide (SSPS); an ordinary type with low molecular weight (SSPS-LMW; molecular weight - 550 kg/mol), and a new type with high molecular weight (SSPS-HMW; molecular weight = 2850 kg/mol). In the current study, the protein stabilizing ability of both types of SSPS was investigated in model acidified milk. We prepared model acidified milk drinks that were composed of 3.0% skimmed milk and 0.4% SSPS-HMW or SSPS-LMW. Model acidified milk was centrifuged at several centrifugal accelerations. The centrifuged samples were visually observed, and the measurement of precipitate weight and turbidity of the upper layer confirmed that SSPS-HMW stabilized proteins better than SSPS-LMW. The model mixture of SSPS-HMW had smaller particle sizes and a larger zeta-potential. In addition, The surface concentration of SSPS-HMW was about 2 times that of SSPS-LMW, indicating that the thicker SSPS-HMW layer produces larger steric repulsion to protein particles. These results clearly demonstrate that SSPS-HMW has a greater ability to disperse milk proteins because of the larger electrostatic repulsive force of polysaccharide chains and the steric repulsive force of the thicker layer that forms on the surface of particles. (c) 2013 Elsevier Ltd. All rights reserved.