Complex Coacervation of Milk Proteins with Sodium Alginate

Beta-lactoglobulin (BLG) and bovine serum albumin (BSA) coacervate formation with sodium alginate (ALG) was investigated by turbidimetric analysis, zeta potential, particle size, viscosity, transmission electron microscopy (TEM) and isothermal titration calorimetric (ITC) measurements as a function of pH (1.0-7.0) and protein/alginate mixing ratio (1:1, 1.5:1, 2:1, 1:0, and 0:1 wt.). Critical pH values of phase transitions for BSA ALG complexes (pH(C), pH(phi 1), and pH phi(phi 2)) representing the formation of soluble and insoluble complexes of a protein ALG mixture (2:1) at pH 4.8, 4.2, and 1.8, respectively. In the case of BLG ALG, critical pH values (pH(C) pH(phi 1), and pH(phi 2)) were found to be 4.8, 4.2, and 1.6, respectively. The pH(opt) values, expressed by the highest optical density, were pH 2.8 for BSA-ALG and 2.4 for BLG-ALG. TEM and zeta-potential results showed that maximum coacervate formation occurred at pH 4.2 for both protein-polysaccharide solutions. The interaction between BLG-ALG and BSA-ALG was spontaneously exothermic at pH 4.2 according to ITC measurements. The findings of this study provide insights to a thorough understanding about the nature of interactions between milk proteins and ALG and formulate new applications for food, pharmaceutical, nutraceutical, and cosmetics applications.