Biosynthesis of triacylglycerols and volatiles in olives

For many reasons (history, myth, oil quality, etc .) olive is unique among the commercially important oil crops. The biochemistry of the olive tree is also singular. From the photosynthetic point of view olive is one of the few species capable of synthesising both polyols (mannitol) and oligosaccharides (raffinose and stachyose) as the final products of the photosynthetic CO 2 fixation in the leaf cell. These carbohydrates, together with sucrose, can be exported from the leaves to the fruits to fulfil the metabolic requirements for oil synthesis. On the other hand, contrary to oilseeds, which are absolutely dependent on the leaves to supply photoassimilates for the synthesis of storage oil, developing olives contain active chloroplasts capable of fixing CO 2 . Thus, the olive contributes to its own carbon economy. In fact, detached olives have been demonstrated to be capable of fixing radiolabelled CO 2 in the light and using the reduced photosynthetic products to form storage oil. Soluble fractions from olive pulp have been demonstrated to catalyse the synthesis of fatty acids from malonyl‐CoA. The properties of this subcellular fraction indicate that fatty acids are formed by the same type of fatty acid synthase complex established for other plant systems. By the same token, glycerolipids, including storage triacylglycerols, are formed from glycerophosphate and acyl‐CoAs according to the Kennedy pathway, as it has been demonstrated in particulate fractions from olive pulp and tissue culture. Also unique to virgin olive oil is its characteristic aroma. The most abundant volatile compounds in the aroma of olive oil are aldehydes and alcohols of six carbon atoms. Such compounds are formed from linoleic and α‐linolenic acids through a sequence of enzymatic reactions known as the lipoxygenase pathway, which is stimulated when olives are crushed during the process of oil extraction. The properties of the different reactions involved in the metabolic pathway leading to the formation of such volatile compounds are described in this paper.