Structure and mechanical properties of acetylated κ-carrageenan gels

κ-Carrageenan (κ-car) is a polysaccharide extracted from red seaweed that is widely used for a range of industrial applications. The rheological and structural properties of κ-car with different degrees of acetylation (DA = 0-45 %) as well as their mixtures were investigated using light scattering, rheology, μ-DSC, and confocal microscopy. Acetylation did not significantly affect the molar mass or radius of κ-car, but it decreased its intrinsic viscosity ([η]). Gelation of κ-car was induced by cooling in the presence of KCl. The critical gelation temperature and storage modulus of the gel decreased with increasing DA and gelation did not occur above 5 °C for DA ≥ 21 %. This was caused by the increasing hindrance from the acetyl groups to form helices, which was confirmed by μ-DSC that showed a decrease of the coil-helix transition temperature and enthalpy. Rheology and μDSC showed that in mixtures of κ-car with different DA, the coil-helix and gelation temperature of each component were the same as for individual solutions. Confocal microscopy images of mixed gels with different fluorescent labels demonstrated co-aggregation of κ-car with different DA without micro-phase separation.