2. Biosynthesis of Plant-Derived Odorants

Plants produce thousands of structurally diverse volatile signal compounds to attract pollinating insects and seed dispersing animals. These compounds are often perceived by humans as a specific fruit or vegetable aroma. Many of these volatiles serve also as defense substances against fungi, bacteria, viruses, and herbivores. The knowledge of precursors and pathways leading to the formation of volatiles in fruits and vegetables has considerably progressed during the last years because of the use of molecular and biochemical techniques. In vitro characterization of the heterologously expressed enzymes has helped clarify the pathways of volatile formation. This chapter will, therefore, provide an overview of biosynthetic sequences and construction mechanisms that are illustrated in most cases using detailed reaction schemes. The various compounds are predominantly ordered according to the biosynthetic pathway that is used in plants to synthesize them and are grouped into carbohydrate-, lipid-, and amino-acid-derived odorants, terpenoids, and glycosidically bound odorants.