Effects of ε‐polylysine or ε‐polylysine hydrochloride on the pH responsive ι‐carrageenan gel

Abstract The binding of oppositely charged polyelectrolytes is a well‐known gel strategy, and pH is an important factor affecting the gel properties. In this work, the influence of pH (3, 5, 7, 9, 11) on the rheological and textural properties, molecular structure and micromorphology of binary mixed gels of ι ‐carrageenan (IC) and ε ‐polylysine (PLL) or ε ‐polylysine hydrochloride (PLH) was investigated. The results showed that a change in pH led to a change in the properties of binary mixed gels. The lower the pH, the higher were G ′, G ″, complex viscosity and gel transition temperature. At the same time, the water holding capacity and gel strength of IC/PLL (IP) and IC/PLH (IPH) were also improved accordingly, and the gel properties of IPH were always better than those of IP. As the pH increased to alkalinity, the density of the gel network structure decreased, the pore size decreased, the pore wall became thinner and the surface smoothed. When the pH dropped into the acidic range, there was a red shift of the hydroxyl group and the sulfate group bands, an enhancement of the hydrogen bonding interaction and a blue shift of the methyl band and the amide I band. At pH 3, the microscopic network structure of IP and IPH were dense and uniform with small pore size, rough surface and thick pore wall. These results showed that the binary mixed gels had better gel properties at pH 3. The results provided a theoretical basis for the preparation of IP and IPH gels, and also enabled a deeper understanding of the mechanism of interaction between polypeptides and carrageenan. © 2023 Society of Industrial Chemistry.