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Acetophenone (AP) and 1-phenylethanol (1PE) are the two major endogenous volatile compounds in flowers of Camellia sinensis var. Yabukita. Until now no information has been available on the biosynthesis of AP and 1PE in plants. Here we propose that AP and 1PE are derived from L-phenylalanine (L-Phe), based on feeding experiments using stable isotope-labeled precursors L-[(2)H(8)]Phe and L-[(13)C(9)]Phe. The subacid conditions in the flowers result in more hydrogenation than dehydrogenation in the transformation between AP and 1PE. Due to the action of some enzyme(s) responsible for the formation of (R)-1PE from AP in the flowers, (R)-1PE is the dominant endogenous steroisomer of 1PE. The modification of 1PE into nonvolatile glycosidic forms is one of the reasons for why only a little 1PE is released from the flowers. The levels of AP, 1PE, and glycosides of 1PE increase during floral development, whereas the level of L-Phe decreases. These metabolites occur mostly in the anthers., (Copyright © 2011 Elsevier GmbH. All rights reserved.)

The potent odorant beta-damascenone was formed directly from 9'-cis-neoxanthin in a model system by peroxyacetic acid oxidation and two-phase thermal degradation without the involvement of enzymatic activity. Beta-damascenone formation was heavily dependent on pH (optimum at 5.0) and temperature, occurring over the two sequential phases. The first was incubation with peroxyacetic acid at 60 degrees C for 90 min, and the second was at above 90 degrees C for 20 min. Only traces of beta-damascenone were formed on application of only one of the two phases. Formate and citrate solutions produced a much better environment for beta-damascenone formation than acetate and phosphate. About 7 microg/L beta-damascenone was formed from 5.8 mg/L 9'-cis-neoxanthin under optimal experimental condition. The detailed pathway by which beta-damascenone is formed remains to be elucidated.