GELLING PROPERTIES OF WATER-SOLUBLE POLYSACCHARIDES FROM PROLIFERATING MARINE GREEN SEAWEEDS (ULVA SPP)

Water-soluble polysaccharides (12.2% of the algal dry weight) were extracted from marine green seaweed (Ulva spp.) which proliferate along the Brittany shores of France. They were composed of 18.4% rhamnose, 4.4% glucose, 1.9% xylose, 0.9% mannose, 0.9% galactose, 15.2% uronic acid, 15.8% sulphate and 23.7% ash based on the extract dry weight. These polysaccharides, formed a weak gel (about 3 Pa) at a concentration of 1.6% (w/v) in deionized water. The elastic modulus increased to about 160 Pa when boric acid (15-33 mm) was added and reached 250 Pa when both boric acid (7 mm) and calcium chloride (7 mm) were present. Adjusting the pH to 7.5 or higher by sodium tetraborate, phosphate or Tris-HCI buffers was detrimental to the gel. These results demonstrate that the poorly exploited biomass of Ulva spp. is a source of gelling polysaccharides of potential economical value. Mechanisms for gel formation which unusually involve both boron and calcium ions are proposed and will be studied further.