ABSTRACT
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.
Subject(s)
Carrageenan/chemistry , Gels/chemistry , Hot Temperature , Rhodophyta/chemistry , Elasticity , Molecular Weight , Structure-Activity Relationship , ViscosityABSTRACT
Extraction parameters (temperature, pH, duration) and alkaline pre-treatment duration have been systematically varied in the aim of exploring their impact on both chemical structure and gelling properties of carrageenan biopolymers obtained from Mastocarpus stellatus seaweeds, collected on the Northern coast of Portugal. Increasing the alkaline pre-treatment duration PT leads to kappa/iota-hybrid carrageenans containing less sulphate groups and biological precursor monomers. As a result, gel properties in the presence of KCl are improved as demonstrated by the increase in the Young's modulus with parameter PT. Increasing the extraction duration t ameliorates the biopolymer yield with no significant change in the complex kappa/iota-hybrid carrageenan chemical structure. However, smaller molecular weights are obtained and gel properties are seen to be negatively affected. Extraction temperature and pH have dramatic effects on the biopolymer gel strength, and a set of extraction parameters optimized with respect to extraction yield and gel properties is reported. In addition, kappa/iota-hybrid carrageenans obtained throughout this study exhibit a wide range of gel strengths in KCl, and allow us to present correlations between gel thermal properties and the kappa/iota-hybrid carrageenans chemical structure.
