Most of the phenolic compounds are derived from the amino acid phenylalanine. Indeed, phenylalanine can be considered the branch point between primary and secondary metabolites. In the steps of the shikimic acid pathway, the removal of the amine function by the enzyme phenylalanine ammonia lyase (PAL) produces the phenylpropanoid compound cinnamic acid. Thus, the two amino acids phenylalanine and tyrosine appear as the precursors in the phenylpropanoid biosynthesis. Furthermore, these phenylpropanoids are then used to elaborate the major phenolic classes, including the avonoids, coumarins, tannins, anthraquinones, anthocyanins, lignin, and lignans.