AGAR FROM GELIDIUM-LATIFOLIUM (RHODOPHYCEAE, GELIDIALES) - BIOCHEMICAL-COMPOSITION AND SEASONAL-VARIATIONS

Gelidium latifolium, collected monthly at Roscoff (Brittany, France) was studied during a one-year period. Gelling properties and chemical composition appeared closely comparable to those of commercial agarose. The agar content of the thalli varied from 26% of the dry weight in March-April to 42.5% in November. An exceptional value of 62% was recorded in December for short, storm eroded thalli. The main components of this agar were 3,6-anhydro-L-galactose (48.5 to 52.2 Molar % of the total amount of sugars) and D-galactose (39.2 to 43.7%). The agar was poorly substituted (3.7 to 4.9% of 6-0-methyl-D-galactose; 1.3 to 2.6% of 2-0-methyl-D-galactose and 2.08 to 2.6% of sulphate groups, pyruvic groups were not detectable on total extract).Glucose was present in small quantities(0.8 to 3.2%). The gel strength increased from 400 g cm-2 in March to around 800 g cm 2 in October and then declined. Gel-strength is not related to the chemical composition of the polysaccharide but to its molecular weight.