Formation and stability of electrostatic complexes formed between scallop female gonad protein isolates and sodium alginate: Influence of pH, total concentration, blend ratio, and ionic strength

The complex coacervation between scallop (Patinopecten yessoensis) female gonad protein isolates (SFGPIs) and sodium alginate (SA) was determined by the turbidimetric method. The impact of pH, total biopolymer concentration, biopolymer blend ratio, and various salt ionic on the mechanisms governing the complex coacervation of SFGPIs-SA complexes were also investigated. For the SFGPIs:SA ratio of 2:1 without adding NaCl, insoluble and soluble complexes were observed at pH 5.8 (pHφ1 ) and pH 8.2 (pHc ) with the optimum biopolymer interactions appearing at pH 2.6 (pHopt ). The maximum turbidity value increased with the increment of the total biopolymer concentration from 0.37 to 1.83 until attaining the critical value (0.75%). As the blend ratios rose from 1:3 to 12:1, the critical pH values (pHc , pHφ1 , and pHopt ) moved to higher pH. Furthermore, the addition of NaCl led to a remarkable decrease in turbidity over the whole pH region in SFGPIs-SA complexes. Moreover, monovalent ions (Na+ and K+ ) had the same effect on the formation of the SFGPIs-SA complex, whereas the divalent cations (Mg2+ and Ca2+ ) lessened the complex formation in comparison with the monovalent ions. This study offers a methodological and theoretical basis for the design of complex SFGPIs-SA systems by understanding the complex coacervation under different conditions. PRACTICAL APPLICATION: In recent years, several protein-polysaccharides complexes have been widely applied in food and biological systems. Scallop (Patinopecten yessoensis) female gonads are deemed as good marine sources for developing protein matrices on account of their high protein content and nutrients. In our study, the effects of different conditions on the mechanisms governing the complex coacervation of SFGPI-SA mixtures were investigated, and the instability of the system could be overcome by understanding the conditions for SFGPIs/SA complex formation, which have a feasible role in developing marine source-protein as a functional food base such as kamaboko gels, can, sausage, fat substitutes, and delivery vehicles for bioactive compounds.