Analysis of the Volatile and Enantiomeric Compounds Emitted by Plumeria rubra L. Flowers Using HS-SPME–GC

The volatile components emitted by fresh aromatic flowers of <i>Plumeria rubra</i> L., harvested in southern Ecuador during three different months were determined to evaluate the fluctuation of secondary metabolites. The volatile compounds were analyzed using headspace solid-phase microextraction (HS-SPME) followed by gas chromatography coupled to mass spectrometry (GC-MS) and a flame ionization detector (GC-FID) using two types of columns: a non-polar (DB-5ms) and polar column (HP-INNOWax). The principal chemical groups were hydrocarbon sesquiterpenes (43.5%; 40.0%), oxygenated sesquiterpenes (23.4%; 26.4%), oxygenated monoterpenes (14.0%; 11.2%), and hydrocarbon monoterpenes (12.7%; 9.3%). The most representative constituents were (E,E)-<i>α</i>-Farnesene (40.9-41.2%; 38.5-50.6%), (E)-nerolidol (21.4-32.6%; 23.2-33.0%), (E)-<i>β</i>-ocimene (4.2-12.5%; 4.5-9.1%), (Z)-dihydro-apofarnesol (6.5-9.9%; 7.6-8.6%), linalool (5.6-8.3%; 3.3-7.8%), and perillene (3.1-5.9%; 3.0-3.2%) in DB-5ms and HP-INNOWax, respectively. Finally, we reported for the first time the enantiomeric distribution of <i>P. rubra</i> flowers, where the enantiomers (1R,5R)-(+)-α-pinene, (S)-(-)-limonene, (S)-(+)-Linalool, and (1S,2R,6R,7R,8R)-(+)-α-copaene were present as enantiomerically pure substances, whereas (S)-(+)-(E)-Nerolidol and (R)-(+)-(E)-Nerolidol were observed as scalemic mixtures. This study provides the first comprehensive and comparative aroma profile of <i>Plumeria rubra</i> cultivated in southern Ecuador and gave us a clue to the variability of <i>P. rubra</i> chemotypes depending on the harvesting time, which could be used for future quality control or applications in phytopharmaceutical and food industries.