Rheological and thermal characteristics of gel structures from various agar fractions

The dynamic rheological properties during gelation, phase transition temperatures and the enthalpy (ΔH) for melting of junction zones in gel networks of different agar fractions were investigated. The results indicated that both gelling (Tgel) and melting (Tm) temperatures, storage moduli (G′) and the ΔH values of agar gels were mainly correlated with their [η] values, rather than with 3,6-anhydro-galactose (3,6-AG) content. Effects of 3,6-AG content on increasing G′ were observed only for the gels of low concentrations (e.g. 0.8 g/dl). The concentration dependences of structural strength and structure development rate, which were presented by G′ and dG′/dt respectively, were found to decrease with increasing 3,6-AG content or [η] value. It is noteworthy that influencing extents of 3,6-AG content and [η] on the above rheological and thermal properties vary not only with the concentration examined, but also with the stage of gelation process