Extraction of antibacterial substances, galactofucoidan and alginate successively from the Gulf of Mannar brown seaweed Sargassum wightii Greville ex J. Agardh

Abstract

In the present study, galactose dominated fucoidan was isolated through successive extraction method in alkaline, acid and neutral pH from the brown seaweed Sargassum wightii Greville ex J. Agardh collected along the Gulf of Mannar (Pamban, India) during March 2011. In this study, crude extracts obtained in chloroform: methanol (1:1 v/v) and 85 % ethanol (at 23°C and 70°C) showed antibacterial activity against Xanthomonas axonopodis pv. citri and X. oryzae pv. oryzae which cause canker in citrus and blight of paddy, respectively. Low (< 3500 Da) and high molecular weight (> 3500 Da) fucoidans separated through DEAE cellulose 52 column were recorded same proportion of monosugars constituents dominating D-galactose over L-fucose. Spectroscopic studies (IR & NMR) of high molecular weight fucoidan (Fraction, A1H) with high sulphate showed higher anticoagulation activity than low molecular weight fucoidan under in vitro APTT assay. This investigation concludes that successive extraction method yields galactofucoidan (3.62 %), alginate (11.2 %) and antibacterial substances (13.34 %) in the same biomass of brown seaweed S. wightii.