Structure of the agarans from the red seaweed Polysiphonia nugrescens. A potential source of hydrocolloids from the Argentine coast

PRADO HJ; MATULEWICZ MC; CIANCIA M

Kobe, Japón

Simposio; XIX INternational Seaweed Symposium; 2007

International Seaweed Association

Structure of the agarans from the red seaweed Polysiphonia nigrescens. A potential source of hydrocolloids from the Argentine coast Prado HJ1, Matulewicz, MC1 & Ciancia, M2 1Departamento de Química Orgánica (CIHIDECAR-CONICET)-Facultad de Ciencias Exactas y Naturales-Universidad de Buenos Aires- Ciudad Universitaria, Pabellón 2-1428 Buenos Aires- Argentina 2Cátedra de Química Orgánica-Departamento de Biología Aplicada y Alimentos-Facultad de Agronomía-Av. San Martín 4453-C1417DSE Buenos Aires-Argentina E-mail: ciancia@agro.uba.ar The red seaweed Polysiphonia nigrescens (Rhodomelaceae) grows abundantly in areas of incipient pollution as that of Mar del Plata, the most popular seaside resort in the Argentine coast, which is also an important fishing port. The seaweed was exhaustively extracted with water at rt., 70 °C and 90 °C and the extracts were analyzed. The major extract (molar ratio Gal:AnGal:sulfate 1:0.57:1.04), obtained at 70 ºC, was fractionated by ion-exchange chromatography and fractions were eluted with water and aqueous solutions of increasing NaCl concentration. Three main fractions were obtained: with water, 2.0 M NaCl and with boiling 4.0 M NaCl. With the exception of this last fraction, separation was achieved, as expected, as a function of the sulfate concentration, with fractions of approximately constant AnGal content, indicating the presence of precursor units. In contrast, the last fraction is an agarose completely sulfated on C-6. Small amounts of 6-O-methylgalactose were present in all the samples and were only important in the fraction eluted with water. These results showed that the starting product was heterogeneous and that the fractionation method was successful. Structural analysis showed that the substitution pattern found for the agarans of P. nigrescens is in agreement with those reported for other species of this genus, but the sulfation degree is higher; the precursor diad found was G6S®LG6S and, in most of the fractions, no free hydroxyl groups on C-6 were detected. These results support the use of the structure of hydrocolloids as a taxonomic criterion at genus level.