Sterols occur naturally in plants and animals; the most familiar type of the latter is cholesterol, which is vital to cellular functioning due to its role in the fluidity of the cell membrane, besides serving as a secondary messenger in developmental signaling. Further­more, cholesterol is a precursor of fat-soluble vitamins and steroid hormones.

The content and type of sterols vary with the alga species: green algae contain 28-isofucocholesterol, cholesterol, 24-methylene-cholesterol, and p-sitosterol, whereas brown algae contain fucosterol, cholesterol and brassicasterol; red algae contain desmosterol, cholesterol, sitosterol, fucosterol, and chalinasterol. The predominant sterol in brown algae, fucosterol, accounts for 83-97% of the total sterol content, whereas desmosterol, in red algae, accounts for 87-93% (Sanchez-Machado, Lopez-Hernandez et al., 2004; Kumar, Ganesan et al., 2008).