has role long-chain fatty acid octadecanoate octadecanoic acid A C18 straight-chain saturated fatty acid component of many animal and vegetable lipids. As well as in the diet, it is used in hardening soaps, softening plastics and in making cosmetics, candles and plastics. octadecane straight-chain saturated fatty acid plant metabolite human metabolite Daphnia magna metabolite algal metabolite