Molecular weight of agar by high temperature type gel permeation chromatography and physical properties

Agar is a polysaccharide which is called agarose and agaropectin. It seems that molecular weight of agar affects physical properties of the gel made from it. In order to investigate the relation between average molecular weight and physical properties, agar was measured by high temperature type gel permeation chromatography (HT-GPC). First, the conditions for measuring agar by HTGPC were investigated. Agar was prepared from Gelidium sp. which were collected in the sea of Azores (Portugal) and Tokushima Prefecture (Japan). The following result was obtained as the optimum conditions for the measurement: eluent, 0.2M NaNO3; temperature, 70°C; column, Ionpak KS-805 (Showa Denko K.K., Tokyo); sample concentration, below 0.2% (w/v). Under these conditions, agar was measured by HT-GPC, and the average molecular weight and the molecular distribution were calculated. The jelly strength and melting point of agar gel decreased with shifting of the molecular weight distribution to lower molecular weight side and with a decrease of, the average molecular weight. A linear relationship was obtained between the average molecular weight and the physical properties, and the weight-average molecular weight was considered as a more reliable indication for this relation.