Distinguishing Foeniculum vulgare fruit from two adulterants by combination of microscopy and GC-MS analysis

Foeniculum vulgare fruit (FVF) is a widely used traditional medicine. However, two adulterants, namely Anethum graveolens fruit (AGF) and Cuminum cyminum fruit (CCF), have been found in use as FVF in China owing to similar appearance and odor. For the purpose of accurate differentiation of the three herbal medicines, extensive anatomical examination and chemical profiling were conducted. Using light microscopy and fluorescence microscopy, the macroscopic and microscopic features of the three species were compared. It was found that some microscopic characteristics, including transverse shape of mericarp, presence or absence of reticulate cells and non-glandular hairs, as well as fluorescence of endocarp, were of diagnostic significance. Moreover, essential oils were qualitatively and semi-quantitatively analyzed using GC-MS. The analytical results indicated significant chemical variations in different species: in FVF, trans-anethole (83.20%) was the predominant volatile compound followed by estragole (5.03%) and limonene (3.45%), while in AGF, the first, second and third compounds with highest content were carvone (42.58%), apiol (20.76%) and limonene (20.32%), and in CCF were cuminlaldehyde (36.00%), 2-caren-10-al (23.25%) and γ-terpinene (9.65%), respectively. In conclusion, the proposed light microscopy coupled with fluorescence microscopy and/or GC-MS analysis allowed successful distinguishing FVF from AGF and CCF.