Effects of pH, protein:polysaccharide ratio, and NaCl-added concentration on whey protein isolate and soluble soybean polysaccharides electrostatic-complexes formation

In the present work, the interaction between whey protein isolate (WPI) and soluble soybean polysaccharide (SSPS) was studied as a function of pH (7.0 to 2.0), WPI:SSPS mass ratio (1:1 to 10:1), and NaCl-added concentration (0 to 100 mM). The interaction was analyzed by ζ-potential, turbidity, and state diagrams. Then, WPI-SSPS complexes were obtained in the optimized conditions of pH (4.0 to 3.5), WPI:SSPS ratio (2:1 to 6:1), and NaCl-added concentration (0 to 100 mM). The complexes were characterized by ζ-potential, particle size, and physical stability in a factorial 3 × 3 design with analysis by response surface methodology. This methodology showed that the characteristics of the WPI-SSPS complexes are modulated by the modification of the studied parameters. By lowering the pH, the complexes showed a ζ-potential closer to 0 and higher physical stability. By decreasing the WPI:SSPS ratio, the complexes showed more negative ζ-potential. Finally, by increasing the NaCl concentration, the complexes showed negative ζ-potential but an increment of mean particle size and polydispersity index. Data obtained in this work is useful to design WPI-SSPS complexes with specific characteristics of size, charge, and physical stability. These complexes could then be applied in food, medicinal or cosmetic matrices for different purposes.