Influence of calcium and potassium ions on the rheological properties and network formation of hybrid gels constructed with iota-carrageenan and Ala-Lys dipeptide

The gelation and microstructural behaviors of Ala-Lys dipeptide/iota-carrageenan (AK/IC) mediated by salts were investigated. Obviously, salt addition prominently exaggerated the synergistic gelation between AK and IC, with storage modulus ( G' ) of AK/IC and IC increasing extensively from 1145 to 9516 Pa or 5919 Pa and from 615 to 9981 Pa or 4693 Pa at 0.1 Hz with 0.5 % CaCl 2 or KCl, respectively, in which CaCl 2 revealed superiority over KCl. Additionally, different states of water in AK/IC gels resisted salt interference. Moreover, a honeycomb structure with denser porous networks coupled with rough entanglement morphology of AK/IC was observed, in which the CaCl 2 -treated group exhibited even smaller pore sizes. The conformational changes of AK/IC induced by salts were reflected by the redshift of –OH groups in AK/IC, insinuating salt-mediated H-bonding in AK/IC. The blueshift of amide I bands and water deformation groups of AK/IC in comparison to AK and IC alone illustrated the electrostatic interactions between them. Furthermore, coordination interaction, hydrogen bonds and hydrophobic interactive were highlighted among IC, AK and CaCl 2 /KCl as reflected by molecular docking.