Rheological Studies of Various Kinds of Agar Gels

Abstract

Concerning four kinds of seaweeds of Gelidiaceae species, rheological studies were carried out on the samples extracted in a range of temperature from 125° to 140°C under a definite condition of extraction.
The concentration of gel was taken at 2% in all samples. Rexation curves up to 4 hr. were obtained within a range of temperature from 25° to 55°C.
These curves were represented by using a 6-element mechanical model consisting of 3 Maxwell elements in parallel. The following results were obtained; When the extraction temperature is raised, elastic constant, E₁ shows a decreasing tendency; namely, E₁ decreases to nearly 20-30% by raising the extraction temperature by 10°C throughout all of the samples. The relaxation time, τ₁ is decreased in the same way accompanying the temperature rise, but its tendency is slower than that of E₁.
The apparent activation energy obtained from the temperature dependence of τ₁ is about 5 kcal/mol.
These results reveal that the nature of the three-dimensional network structure within an agar gel is independent from sources and extraction temperature.