A new procedure for determining the heterogeneity of agar polymers in the cell walls of Gracilaria spp. (Gracilariaceae, Rhodophyta)

Abstract

The heterogeneity of agar polymers in the cell walls of Gracilaria tenuistipitata, G. eucheumoides, and G. blodgettii was demonstrated by sequential extraction of the algae in water at 22 °C; in boiling 80, 60, 40, and 20% ethanol–water solutions; and in water at 100 and 121 °C. Agar polymers in each extract were analyzed by 1H and 13C nuclear magnetic resonance spectroscopy. The agar polymers extracted from the three algae with water at 22 °C had a high concentration of repeat units substituted by alkali-labile sulfate. Methylated agar polymers were extracted with boiling 80 and 60% ethanol from G. tenuistipitata and G. eucheumoides, the former having a high content of 6-O-methyl-D-galactose and a low concentration of 2-O-methyl-3,6-anhydro-L-galactose and the latter consisting mainly of 2-O-methyl-3,6-anhydro-L-galactose. Sulfated agar polymers (alkali-stable sulfate) were extracted from G. tenuistipitata and G. blodgettii with boiling 20% ethanol and water (100 and 121 °C). Floridean starch was detected by 13C nuclear magnetic resonance in the extracts from G. tenuistipitata and G. eucheumoides.