In vitro biological activities of essential oils from the Cameroonian spices Afrostyrax lepidophyllus Mildbr. and Scorodophloeus zenkeri Harms rich in sulphur-containing compounds

The essential oils obtained from the seeds of bush onion (Afrostyrax lepidophyllus) and tropical garlic tree (Scorodophloeus zenkeri), which are sold in the Cameroonian market as spices to be used in the African traditional cuisine, were analyzed for chemical composition by GC-FID and GC/MS, and for in vitro biological activities, namely cytotoxic, antioxidant and antimicrobial, by MTT, DPPH, ABTS and agar disc diffusion method. Both oils were composed mainly by sulphur-containing compounds providing the typical garlic- and onion-like odors of spices. They accounted for 91.0-96.1% of the total compositions. The predominant compound in both oils, 2,4,5,7-tetrathiaoctane (51.5-52.9%), was isolated by preparative TLC and structurally elucidated by 1H and 13C-NMR data. The oils exhibited a strong inhibitory effect on the human cancer cells, namely T98G cells (human glioblastoma multiforme cell line), MDA-MB 231 cells (human breast adenocarcinoma cell line), A375 cells (human malignant melanoma cell line) and HCT116 cells (human colon carcinoma cell line), and a good scavenging activity against DPPH and ABTS+ radicals, while negligible was the antimicrobial effects. The volatile compositions of A. lepidophyllus and S. zenkeri oils support their use as odorous spices. The significant inhibition activities detected make these oils worthy of further investigation as promising chemopreventive agents to be exploited in the African pharmaceutical market.