Thermal and viscoelastic properties of kappa/iota-hybrid carrageenan gels obtained from the Portuguese seaweed Mastocarpus stellatus.

The potential use of the underexploited Portuguese seaweed Mastocarpus stellatus as a source of natural thickening and gelling agents for food applications has been investigated. The alkaline pretreatment duration and extraction parameters (pH, temperature, and extraction duration) of seaweeds have been systematically varied in order to produce kappa/iota-hybrid carrageenans exhibiting a wide range of chemical properties. The mechanical spectra and the setting and melting temperatures of gels obtained by cooling 1.5 wt % extracted biopolymers solutions in 0.05 mol/dm3 KCl were measured by means of small amplitude oscillatory shear experiments. Gels showing elastic storage moduli ranging from 250 to 2750 Pa with no water syneresis could be obtained, and the relationships between the thermal properties and elasticity of the gels were evidenced. Gels mechanical properties are shown to correlate well with polysaccharides chemical parameters such as the degree of sulfate groups, the molecular weight distribution, and the relative content in iota-carrageenan monomers as determined by FTIR spectroscopy.