Fucoidan/κ-carrageenan mixed gel: Effect of anions of different valence including chloride, bromide, iodide, sulfate and phosphate

The effects of the differently charged anions, NaCl, NaBr, NaI, Na2SO4, and Na3PO4 on the gel properties and structure of the fucoidan/kappa-carrageenan mixed gel (FC) were investigated using the rheometer, texture analyzer, LF-NMR, Cryo-SEM, FT-IR, and XRD. At a certain concentration, Cl- and Br- could stabilize the helical conformation of the gel through electrostatic shielding. The addition of SO42- and PO43- would reduce the strength of the gel. And I- would soften the gel. With increasing anion concentration, the electrostatic repulsion between FUC and KC was gradually enhanced. The FUC dispersions remained liquid after the addition of anions, while FC gelled depending on the type and concentration of anions. The elastic modulus increased with increasing concentration of NaCl and NaBr, but decreased with increasing concentration of NaI, Na2SO4, and Na3PO4. Moreover, the addition of anions promoted the water migration of FC, as reflected by the T-23 relaxation time changing from high to low and the significantly higher migration of NaCl and NaBr than NaI and Na2SO4. The pores of the gel microstructure change from disordered to uniform. The FT-IR and XRD results were well related to the structural changes. There is electrostatic repulsion between anion and FC, and the binding ability of FC to monovalent anions and trivalent anions is better than that of divalent anions. Overall, this study could provide a theoretical basis for the design and development of FUC-based gels.

Automated summary

The effects of differently charged anions (NaCl, NaBr, NaI, Na2SO4, and Na3PO4) on the gel properties and structure of the fucoidan/kappa-carrageenan mixed gel (FC) were investigated through various techniques. Cl- and Br- stabilized the gel's conformation, while SO42- and PO43- weakened the gel's strength, and I- softened the gel. With increasing anion concentration, electrostatic repulsion between FUC and KC was enhanced. The addition of anions affected the gel's water migration and microstructure. Overall, this study provides a theoretical basis for the design of FUC-based gels.