Influence of pH and blend ratios on the complex coacervation and synergistic enhancement in composite hydrogels from scallop (patinopecten yessoensis) protein hydrolysates and Kappa-carrageenan/xanthan gum

The purpose of this study was to characterize the electrostatic complexation between scallop Patinopecten yessoensis male gonad hydrolysates (SMGHs) and Kappa-carrageenan/xanthan gum (KC/XG) within pH 12-1 at different hydrolysate/polysaccharide ratios (9:1-1:9) and to investigate the influence of pH and ratios on gelation and microstructural properties for widening the application of marine-derived source. According to the phase diagram of SMGHs/KC/XG, pH(c) hold a constant value around pH 8.5, pH(phi 1) gradually shifted from 4.2 to 2.8, and pH(max) fluctuated within 2.4-1.4 as ratios decreasing from 9:1-2:8. Additionally, SMGHs/KC/XG showed higher gel strength in acid condition, as decreasing pH promoted the electrostatic attractive interactions within positively charged patches in SMGHs and negatively charged sulfate and carboxyl groups in KC/XG causing more tightly packed structures formation. Moreover, decreasing ratios from 9:1 to 3:7 could further enhance the gel strength of SMGHs/KC/XG, ascribing to the stronger gelation ability of polysaccharides and enough neutralization. Moreover, SMGHs/KC/XG exhibited well-organized microstructures with smaller pore sizes, denser and more homogeneous networks at more acid domains, supporting stronger gel strength. Therefore, this study provides theoretical and methodological basis for designing novel SMGHs/KC/XG hydrogels with considerable gel strength and microstructures through understanding the complex coacervation at different pH and ratios.