Relationships between gel forming ability and molecular weight distribution of agar

Abstract

In the case of no correlation between the agar gel strength and contents of sulfate ester and 3,6-anhydro-L-galactose, or the molecular weight, effect of molecular weight distribution was examined to gel forming ability. Low molecular weight agar (M_w= 0.26×10⁵) was added to four agars with different molecular weight and molecular weight distribution. In three agars (M_w = 0.82, 1.03, 1.92×10⁵) containing large amount of low molecular weight fraction and showing high gel strength, the gel strength and the gel fracture energy by adding low molecular weight agar of 5 wt％ were about 15％ and 50％ reduction, respectively. On the other hand, in an agar (M_w = 1.90×10⁵) containing small amount of low molecular weight fraction and showing low gel strength, the gel strength and the gel fracture energy were about 10% reduction by adding low molecular weight agar of 16 wt％. Therefore, the reinforcement effect to gel strength by small molecule was estimated. If in two agars with the same average molecular weight, an agar containing large amount of both high and low molecular weight fractions was expected to show high gel forming ability.