Sterols compositions, antibacterial, and antifouling properties from two Malaysian seaweeds: Dictyota dichotoma and Sargassum granuliferum -

Seaweeds are the major principle producers of oceanic plant community, distributed widely and indigenously and are recognized for their elaborate chemical defense characteristic against many biotic and abiotic factors. A variety of seaweed biogenic compounds exhibiting antifouling activity, which belongs to the group of fatty acids, lipopeptides, amides, alkaloids and sterols were discovered. In this study, D. dichotoma and S. granuliferum collected from Pulau Nunuyan Laut, Sabah, Malaysia were studied to determine its sterol composition and isolation was carried out to isolate their pure sterol compounds. Two assays consist of disc diffusion method for antibacterial activity and crystal violet assay were carried out to study its antifouling activity. Campesterol, stigmasterol and β-sitosterol were the dominant sterol compound detected in both sample and six pure sterols were isolated (compound 1-6). Results from antibacteria and antifouling analysis showed better inhibition for gram negative compared to gram positive bacteria. Fucosterol (4) and epicoprostanol (5) gave best antibacteria activity with two bacteria inhibited compared to other compound. Meanwhile, coprostanol (1), campesterol (2), stigmasterol (3), epicoprostanol (5) and 5β-cholestan-3-one (6) showed strong antifouling activity towards the selected bacterial strains with IC50 values ranges from 266.3-425.8 µg/mL.