Diversity in principal constituents of plants with a lemony scent and the predominance of citral.

In this study, we extracted essential oils from four species of plants with lemony scents (Melissa officinalis L., Aloysia citriodora Palau (= Lippia citriodora (Palau) Kunth), Thymus × citriodorus, Perilla citriodora (Makino) Nakai). We then examined the components of extracts using gas chromatography (GC) and GC-mass spectrometry (GC-MS). A comparison of components indicated that the largest proportions of essential oils were caryophyllene (25%) in M. officinalis, geraniol (50%) in T. citriodorus, and citral (61 and 82%) in A. citriodora and P. citriodora. Moreover, we used a sensory evaluation method using dilute aqueous solutions of extract components, citral, linalool, d-limonene, and geraniol, to select the mixture with a flavor that mostly resembled lemon. The participants in the study felt that an aqueous citral solution flavored more like lemon than aqueous d-limonene. Furthermore, an open field study of sedative effects of citral and d-limonene, when inhaled, on mice demonstrated that citral exhibited a sedative effect at a lower concentration than that of d-limonene.