Rheological elucidation of the viscoelastic properties and network interaction of mixed high-methoxyl pectin and kappa-carrageenan gels

The interaction between two anionic polysaccharides known for their gelation capability was investigated. Mixtures of high-methoxyl pectin (HMP) and kappa-carrageenan (KC) were prepared at different volume fractions. The sample's complex rheological properties and microstructures were investigated by performing linear small amplitude oscillatory shear (SAOS) and nonlinear large amplitude oscillatory shear (LAOS). Pure KC and the HMP/KC mixtures exhibited gel-like properties, whereas pure HMP did not gel at the experimental conditions employed and was characterized as a viscoelastic liquid. Temperature-dependent rheological behavior of HMP/ KC mixtures suggested the independent aggregation of KC chains. The viscoelastic properties of the HMP/KC mixtures, such as oscillatory spectrum, and material stiffness, followed that of pure KC, indicating that KC strongly influenced the final gel. The transient behavior of the HMP/KC mixtures in the time sweep and the monotonic decrease of the storage modulus in the linear regime, and the onset of nonlinear rheological behavior in the strain sweep measurements suggested the possibility of the phase-separated network structure of in HMP-rich and KC-rich phases in the mixtures. Based on the rheological data both in the linear and nonlinear regimes, we propose the possibility of a bicontinuous network structure in HMP/KC mixtures, composed of the weak HMP phase in random coil configuration and the dominant KC phase in double helix aggregates.