agar (äˈgär, āˈ–, ăgˈär) [key], product obtained from several species of red algae, or seaweed, chiefly from the Ceylon, or Jaffna, moss ( Gracilaria lichenoides ) and species of Gelidium, harvested in eastern Asia and California. Chemically, agar is a polymer made up of subunits of the sugar galactose; it is a component of the algae's cell walls. Dissolved in boiling water and cooled, agar becomes gelatinous; its chief uses are as a culture medium (particularly for bacteria) and as a laxative, but it serves also as a thickening for soups and sauces, in jellies and ice cream, in cosmetics, for clarifying beverages, and for sizing fabrics. See also Rhodophyta.
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