Polysaccharides from the red seaweed Gracilaria dura (Gracilariales, Rhodophyta)

The yield and physical and chemical properties of agars from Gracilaria dura (C. Agardh) J. Agardh, harvested in Thau lagoon (Mediterranean sea, France), were investigated. The agar yield ranged from 32% to 35%. Gel strength of agar ranged from 263 to 600 g cm−2, with the maximum observed in October. A positive correlation was found between agar yield and gel strength (r=0.82; P<0.01). The gelling temperature followed the same pattern of gel strength and also showed higher value in October (43 °C). The nitrogen content varied from 1.04 ± 0.60% (June) to 4.70 ± 0.01% (October). A positive correlation was noted between nitrogen content and gel strength (r=0.77; P<0.05). The 3,6-anhydrogalactose content ranged from 0.70 to 0.84 and showed monthly significant differences (P<0.05). There was a positive correlation between 3,6-anhydrogalactose content and gel strength. The values of sulfate content were relatively constant during the studied period and no significant differences were observed. The relative high gel strength indicates that this species may be considered as source of agar for commercial use.