In vitro biological activities of seed essential oils from the Cameroonian spices Afrostyrax lepidophyllus MILDBR. and Scorodophloeus zenkeri HARMS rich in sulfur-containing compounds

Abstract

The chemical composition of the essential oils obtained from the seeds of bush onion (Afrostyrax lepidophyllus) and tropical garlic tree (Scorodophloeus zenkeri), plants used as spices in the traditional African cuisine, was determined by GC-FID and GC/MS analyses. Moreover, in vitro biological properties of the oils, namely, the cytotoxic, antioxidant, and antimicrobial activities, were investigated by the MTT, the DPPH(.) and ABTS(.+) scavenging, and the agar disc-diffusion methods, respectively. Both oils were composed mainly by S-containing compounds, accounting for 91.0-96.1% of the total oil compositions, which provided them the typical garlic- and onion-like odors of spices. The predominant compound in both oils, 2,4,5,7-tetrathiaoctane (1; 51.5-52.9%), was isolated by preparative TLC and structurally elucidated by (1) H- and (13) C-NMR data. The oils exhibited a strong inhibitory effect on the growth of human cancer cells, namely, T98G (human glioblastoma multiforme cell line), MDA-MB 231 (human breast adenocarcinoma cell line), A375 (human malignant melanoma cell line), and HCT116 (human colon carcinoma cell line) cells, and a good DPPH(.) - and ABTS(.+) -scavenging activity, while the antimicrobial effects were negligible. The volatile compositions of A. lepidophyllus and S. zenkeri oils supported 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.

Keywords: Afrostyrax lepidophyllus; Antimicrobial activity; Antioxidant activity; Cytotoxic activity; Essential oils; Scorodophloeus zenkeri.