Method of processing seaweed

A method of processing seaweed which comprises the following steps:

• (i) treating seaweed with an alcohol having one to six carbon atoms to form an alcoholic fraction and an insoluble first seaweed residue;
• (ii) separating the alcoholic fraction;
• (iii) removing the alcohol from the alcoholic fraction to form a concentrate comprising biologically active compounds;
• (iv) extracting the first seaweed residue with an aqueous solution at a pH of less than about 6 to form an aqueous first extract and an insoluble second seaweed residue;
• (v) optionally concentrating the first extract;
• (vi) adjusting the pH of the first extract (iv) or the concentrated extract of (v) to a value in the range of about 5 to about 8 to obtain a first polysaccharide fraction comprising a mixture of laminaran and fucoidan;
• (vii) extracting the second seaweed residue with water at a temperature of 40 to 100° to form an aqueous second extract and an insoluble third seaweed residue;
• (viii) concentrating the second extract;
• and drying the concentrate to obtain a second polysaccharide fraction comprising a mixture of laminaran, fucoidan, and polymannuronic acid;
• and
• (ix) acidifying the second polysaccharide fraction to a pH not higher than 2.5 to precipitate polymannuronic acid;
• and separating the polymannuronic acid.