Phase separation and formation of sodium caseinate/pectin complex coacervates: effects of pH on the complexation

Abstract

Abstract Background The electrostatic interactions between polysaccharides and proteins are an interesting field in the complex coacervation. PH and mixing ratio have major effect on the complexation and the coacervates structure. Hence, it is necessary to find the optimum pH and mixing ratio of the coacervates as well as understanding the thermal, mechanical, and structural characterization of the coacervates. Thus, structural changes of the complexes of sodium caseinate (NaCas) and high methoxyl pectin as a function of pH (2.00–7.00), biopolymer ratios (1:1, 2:1, 4:1, and 8:1), and total biopolymer concentration (0.1, 0.2, and 0.4% w/v) were evaluated by light scattering and ζ-potential measurements. The phase separation behavior of the NaCas/HMP coacervate and its kinetics turbidity were also investigated via monitoring the turbidity profiles. Moreover, the thermal, rheological and structural behavior of the coacervates was evaluated at the selected pH values. Results The highest turbidity, particle size, and viscosity were achieved at pHmax = 3.30 and formation or dissociation around the pHmax was confirmed by particle size and FTIR. The optimum condition for the coacervation of NaCas and HMP was obtained at ratio 4:1 and 0.4% w/v. Thermal and mechanical stability of the NaCas/HMP coacervates was improved at pH 3.30. By increasing the total concentration of biopolymers, the NaCas/pectin ratio shifted to higher pH values. Furthermore, the maximum coacervate yield was achieved at 39.8% w/w at a ratio of 4:1 of NaCas/HMP and a total biopolymer concentration of 0.4% w/v. Conclusion Phase separation behavior of the coacervates exhibited the optimum pH in coacervation between NaCas and HMP. Furthermore, the rheological, thermal and structural stability of the coacervates were improved in comparison with the single biopolymers. Graphical Abstract

Keywords

• High methoxyl pectin
• Caseinate
• Complex coacervation
• Electrostatic interactions
• Turbidity