YIELD, CHEMICAL-COMPOSITION AND GEL STRENGTH OF AGAROCOLLOIDS OF GRACILARIA-GRACILIS, GRACILARIOPSIS-LONGISSIMA AND THE NEWLY REPORTED GRACILARIA CF. VERMICULOPHYLLA FROM ROSCOFF (BRITTANY, FRANCE)

Agarocolloids were extracted from field samples of Gracilaria gracilis , Gracilariopsis longissima and the newly reported Gracilaria cf. verm iculophylla harvested at different periods of the year near Roscoff (F rance). Native and alkali modified extracts were characterized by GLC, HPLC and FT-IR spectroscopy. The main components of agarocolloids iso lated by freeze-thawing method, were 3,6-anhydrogalactose and galactos e. In addition, minor components (6-O-methyl-galactose, 4-O-methyl-gal actose and sulfate groups ranging from 4.4 up to 6.6% [w/w]) were dete cted. The highest rate of 6-O-methylgalactose was observed in agarocol loids from G. vermiculophylla (14 mole%). Sulfates were mainly branche d on C4 of the D-galactose in G. gracilis and Gs. longissima agarocoll oids. G. vermiculophylla agaroids isolated by EtOH and NaCl precipitat ions from the syneresis water were characterized by a high sulfation o n C6 of galactose and a low sulfation on C2 of 3,6-anhydrogalactose. N ative agarocolloid gel strengths from Gracilaria species were clearly higher than those of Gracilariopsis. Alkali treatments reduced the sul fate levels but increased slightly the gel strengths. An approximation of the polymer sizes carried out with colorimetric assays indicated t hat the polymer sizes were higher in G. gracilis than observed in Gs. longissima.