Gelation of cassia gum by freezing and thawing

Aqueous solution of cassia gum (CG), which is categorized as a galactomannan polysaccharide having mannose/galactose ratio = 5/1, forms hydrogels by freezing and thawing. When frozen CG aqueous solution was thawed, transparent sol was separated from a turbid gel, i.e. syneresis occurred. Gel concentration ({(Mass of dry gel) / (Mass of gel)} × 100) increased with increasing CG concentration. Viscoelastic properties of CG hydrogels formed by freezing and thawing were investigated by thermomechanical analysis (TMA) in water using an oscillation mode at 0.05 Hz. Dynamic modulus (E′) increased from 3 kPa to ca. 5 kPa with increasing freezing rate. In contrast, E′ maintained a constant value regardless of repeating number of freezing and thawing. From TMA results, it is concluded that the density of cross-linking network structure depends on the size of ice formed by freezing. At the same time, the low E′ value of CG gels is ascribed to the fact that association of galactosyl side group is disturbed by the stiff chain attributed to the unsubstituted region of CG