Alginates are linear polysaccharides found in the brown seaweeds (Phaeophyceae). They contain β(1,4)-linked mannuronic acid and α-(1,4)-linked guluronic acid in blocks of polymannuronic acid (M-blocks), polyguluronic acid (G-blocks) and alternating M&G (MG blocks). Oligosaccharides derived from alginates are produced either by enzymatic action (alginate lyase) or acid hydrolysis. However, the enzyme-derived oligosaccharides differ from those produced by acid hydrolysis as the enzyme derived products are unsaturated with a double bond between positions 4-5 at the non-reducing terminal. Acid-derived oligosaccharides do not have this feature and are fully saturated although they are much more difficult to produce due to the electron-withdrawing nature of the carboxyl group. It is for this reason that most studies have been undertaken with unsaturated enzyme-derived oligomers. Claims have been made in a number of publications that these oligosaccharides have antioxidant properties when used as food additives. Other reports suggest that they can act as growth-promoters in agriculture and that they may possess anti-tumoral and anti-inflammatory activity.