Valorization and identification of bioactive compounds of a spice Ammodaucus leucotrichus

Ammodaucus leucotrichus Cosson & Durieu is a spice largely used in traditional medicine in North African countries especially in Algerian Sahara. This study was conducted to identify the phenolic compounds of aerial parts organic extracts and also to evaluate their in vitro antioxidant and antimicrobial activities. The antioxidant activity was assessed by three methods: DPPH reducing activity, ferric reducing power and phosphomolybdate method. The antimicrobial activity was assessed against fifteen pathogen reference microbial strains using Agar diffusion and broth microdilution assays. HPLC analysis allowed the identification of two flavonoids (naringenin and quercetin), three phenolic acids (sinapic, ferulic and p-coumaric) and vanillin. It was found that the highest abundance in polyphenol, flavonoid and flavonol contents and also the strongest antioxidant activities were recorded in the ethyl acetate and n-butanol fractions with IC50 for DPPH assay of 30 ± 1.4 µg/mL, EC50 for FRAP assay of 24 ± 1.1 µg/mL and a reductive activity on phosphomolybdate of 134.79 ± 1.8 µg AAE/mg. The extracts showed a broad spectrum of antimicrobial activities for the most tested microorganisms with inhibition zones ranging from 7 to 10 mm and MIC values ranging from 3.125 to 25 mg/mL. The most interesting activities were attributed to the ethyl acetate fractions notably against Bacillus cereus, Bacillus subtilis, Staphylococcus aureus, Listeria monocytogenes, Acinetobacter baumannii and Micrococcus luteus. These results pointed out that A. leucotrichus exhibit an appreciable antibacterial and antioxidant activities which are probably due to the wide range, the high contents of phenolic classes of secondary metabolites detected and the synergistic interactions between them.