Rheology of highly elastic iota-carrageenan/kappa-carrageenan/xanthan/konjac glucomannan gels

Mixed gels containing κ-carrageenan, ι-carrageenan, konjac glucomannan and xanthan were investigated. In binary mixtures, the only interactions identified from differential scanning calorimetry were between konjac glucomannan and κ-carrageenan or xanthan. The effect of konjac addition on κ-carrageenan-ι-carrageenan mixed gels was similar to that on κ-carrageenan gels, namely, an initial increase of the elastic modulus was observed up to a certain stoichiometric ratio, followed by a plateau of the elastic modulus and a strong increase of the fracture strain when konjac was added in excess. Addition of xanthan led to maxima and minima of the elastic modulus and fracture strain and stress. Interestingly, characteristic features of the elastic modulus appeared at the same concentration of xanthan added to kappa-carrageenan/konjac glucomannan mixtures with or without iota-carrageenan, indicating that xanthan is present in the kappa-carrageenan/konjac phase and absent from the iota-carrageenan phase. Characteristic features of the fracture properties, however, were shifted to higher concentrations of xanthan when iota-carrageenan was added. We tentatively conclude that xanthan chains that are concentrated in the kappa-carrageenan/konjac phase under quiescent conditions achieve homogeneous distribution under large mechanical deformation.