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Studying the noncovalent interactions between proteins and polysaccharides is quite important mainly due to the wide number of applications such as developing pH-responsive complexes. Scallop Patinopecten yessoensis male gonad hydrolysates‑sodium alginate (SMGHs-SA) was investigated as noncovalent complexes at pH from 1 to 10. The critical pH values pH C (around 6) and pHφ (around 4) were independent of the SMGHs-SA ratio, indicating the formation of soluble and insoluble complexes. The pH response of SMGHs-SA complexes was evaluated by investigating the rheological behavior, moisture distribution, functional group change and microstructure. Compared to the co-soluble and soluble complexes phases, the SMGHs-SA complexes had a higher storage modulus and viscosity as well as a lower relaxation time (T 23) in the insoluble complexes phase (pHφ>3). Additionally, the amide I band and COO− stretching vibration peaks were redshifted and the amide A band vibration peaks were blueshifted by acidification. Electrostatic interactions and intermolecular/intramolecular hydrogen bonding led to SMGHs-SA agglomeration at pH 3, forming a uniform and dense gel network structure with strong gel strength and water-retention capacity. This study provides a theoretical and methodological basis for the design of novel pH-responsive complexes by studying SMGHs-SA complex coacervation. • Scallop gonad hydrolysates (SMGHs) and sodium alginate (SA) could coacervate. • Acidification promoted the formation of SMGHs-SA coacervations. • Electrostatic interactions were the main force for the SMGHs-SA complex at pH 3. • Hydrogen bonding also drove the interaction of SMGHs and SA. [ABSTRACT FROM AUTHOR]

Studying the noncovalent interactions between proteins and polysaccharides is quite important mainly due to the wide number of applications such as developing pH-responsive complexes. Scallop Patinopecten yessoensis male gonad hydrolysates‑sodium alginate (SMGHs-SA) was investigated as noncovalent complexes at pH from 1 to 10. The critical pH values pH C (around 6) and pHφ (around 4) were independent of the SMGHs-SA ratio, indicating the formation of soluble and insoluble complexes. The pH response of SMGHs-SA complexes was evaluated by investigating the rheological behavior, moisture distribution, functional group change and microstructure. Compared to the co-soluble and soluble complexes phases, the SMGHs-SA complexes had a higher storage modulus and viscosity as well as a lower relaxation time (T 23) in the insoluble complexes phase (pHφ>3). Additionally, the amide I band and COO− stretching vibration peaks were redshifted and the amide A band vibration peaks were blueshifted by acidification. Electrostatic interactions and intermolecular/intramolecular hydrogen bonding led to SMGHs-SA agglomeration at pH 3, forming a uniform and dense gel network structure with strong gel strength and water-retention capacity. This study provides a theoretical and methodological basis for the design of novel pH-responsive complexes by studying SMGHs-SA complex coacervation. • Scallop gonad hydrolysates (SMGHs) and sodium alginate (SA) could coacervate. • Acidification promoted the formation of SMGHs-SA coacervations. • Electrostatic interactions were the main force for the SMGHs-SA complex at pH 3. • Hydrogen bonding also drove the interaction of SMGHs and SA. [ABSTRACT FROM AUTHOR]

The purpose of this study was to characterize the electrostatic complexation between scallop Patinopecten yessoensis male gonad hydrolysates (SMGHs) and κ -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 φ1 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. • pH and ratio largely regulate turbidity changes of SMGHs/KC/XG complexes. • pH c exhibits ratio-independent, and pH φ1 , pH max exhibit ratio-dependent behaviors. • Higher KC/XG proportion supports stronger gel strength in soluble phases. • More SMGHs/KC/XG neutralization promotes gel formation in insoluble coacervate phase. • SMGHs/KC/XG exhibits well-organized and compact networks at acid condition. [ABSTRACT FROM AUTHOR]