Extraction and quantification of edible alginates from selected brown algae species in Ahangama and Beruwala rocky intertidal reefs, Sri Lanka.

Abstract

Seaweeds are comprised with large concentrations of polysaccharides and bioactive compounds. Sodium Alginate (SA) extracted from brown algae is a biodegradable, non-toxic polymer and it is the most adaptable polysaccharide found in nature. Sri Lanka harbours a rich diversity of macroalgae enriched with bioactive compounds and polysaccharides such as SA. This study was carried out to extract and quantify the SA content of brown algae Sargassum crassifolium, Sargassum ilicifolium, Sargassum turbinatifolium, Padina sp., Dictyota sp., and Turbinaria ornata in Ahangama and Beruwala rocky reefs in 2023. Fresh samples 1 kg of each species were collected from two sites. The SA was extracted and validated by using FT-IR spectroscopy. Among the species collected, S. crassifolium had the highest mean yield of SA (Ahangama; 1.9502 ± 0.0979% DW, Beruwala; 1.7897 ± 0.0100 % DW) and Padina sp. had recorded the lowest mean of SA (Ahangama; 0.3393 ± 0.0055% DW, Beruwala; 0.0046 ± 0.0002 % DW). ANOVA tests were conducted to determine statistical significance. There was a significant difference in the SA yield among the different brown seaweed species in the Ahangama study site (F (3,33) = 13.004, p < 0.05). S crassifolium, S ilicifolium, S turbinatifolium and Padina sp. of Ahangama reef have also recorded a higher yield of SA than the Beruwala reef (F (3,33) = 13.004, p < 0.05). Moreover, methanolic extracts gained from selected seaweeds exert a wide range of functional groups such as O-H stretching for Alcohol and Phenol, C-C stretching for Aromatics, C-N stretching for Aliphatic amines etc. Results of this study revealed that SA yield varies among brown algae species as well as the same species in different locations and all alginate levels of the species were lower than the previous studies. Although the SA extraction method was not appropriate for the production of alginate at an industrial scale, it was effective in obtaining pure alginate.