Diferulic acids  Diferulic acids (also known as dehydrodiferulic acids) are organic compounds that have the general chemical formula C20H18O8, they are formed by dimerisation of ferulic acid. Curcumin and curcuminoids, though having a structure resembling diferulic acids', are not formed that way but through a condensation process. Just as ferulic acid is not the proper IUPAC name, the diferulic acids also tend to have trivial names that are more commonly used than the correct IUPAC name. Diferulic acids are found in plant cell walls, particularly those of grasses. There are currently nine known structures for diferulic acids. They are usually named after the positions on each molecule that form the bond between them. Included in the group are 8,5'-DiFA (DC) (or decarboxylated form) and 8,8'-DiFA (THF) (or tetrahydrofuran form), which are not true diferulic acids, but probably have a similar biological function. The 8,5'-DiFA (DC) lost CO2 during its formation, the 8,8'-DiFA (THF) gained H2O during its formation. 8,5'-DiFA (BF) is the benzofuran form. Ferulic acid can also form trimers and tetramers, known as triferulic and tetraferulic acids respectively. They have been found in the cell walls of most plants, but are present at higher levels in the grasses (Poaceae) and also sugar beet and Chinese water chestnut. The 8-O-4'-DiFA tends to predominate in grasses, but 5,5'-DiFA predominates in barley bran. Rye bread contains ferulic acid dehydrodimers. In chufa (tiger nut, "Cyperus esculentus") and sugar beet the predominant diferulic acids are 8-O-4'-DiFA and 8,5'-DiFA respectively. 8-5' Non cyclic diferulic acid has been identified to be covalently linked to carbohydrate moieties of the arabinogalactan-protein fraction of gum arabic. Diferulic acids are thought to have a structural function in plant cell walls, where they form cross-links between polysaccharide chains. They have been extracted attached to a few sugar molecules at both ends, but so far no definitive proof of them linking separate polysaccharide chains has been found.