Algae and Men
  Sources and Uses of Commercial Algae
    - Food
      - Cyanophyta
      - Rhodophyta 
      - Heterokontophyta
      - Chlorophyta
    - Extracts 
      - Agar
      - Alginate 
      - Carrageenan
    - Animal Feed
    - Fertilizers 
    - Cosmetics 
    - Therapeutic Supplements 
    - Toxin
Agar, alginate (derivative of alginic acid), and carrageenan are three hydrocolloids that are extracted from various red and brown macroalgae. A hydrocolloid is a non-crystalline substance with very large molecules, which dissolves in water to give a thickened (viscous) solution. Agar, alginate, and carrageenan are water-soluble carbohydrates used to thicken aqueous solutions, to form gels (jellies) of varying degrees of firmness, to form water-soluble films, and to stabilize certain products, such as ice-cream (they inhibit the formation of large ice crystals, allowing the ice-cream to retain a smooth texture). The use of macroalgae as a source of these hydrocolloids dates back to 1658, when the gelling properties of agar, extracted with hot water from a red macroalgae, were first discovered in Japan. Extracts of Irish moss (Chondrus crispus), another red macroalgae, contain carrageenan and were popular as thickening agents in the 19th century. It was not until the 1930s that extracts of brown macroalgae, containing alginate, were produced commercially and sold as thickening and gelling agents.

Industrial uses of macroalgae extracts expanded rapidly after the Second World War, but were sometimes limited by the availability of raw materials. Once again, research into life cycles has led to the development of cultivation industries that now supply a high proportion of the raw materials for some hydrocolloids. Today, approximately 1 million tons of wet macroalgae are harvested annually and extracted to produce the above three hydrocolloids. Total hydrocolloid production is in the region of 55,000 tons/yr, with a value of 585 million U.S. dollars.

There are a number of artificial products reputed to be suitable replacements for macroalgae gums but none have the exact gelling and viscosity properties of macroalgae gums and it is very unlikely that macroalgae will be replaced as the source of these polysaccharides in the near future.