Évaluation de potentiel antimicrobien et antioxydant des graines de Silybum marianum L

Abstract

Silybum marianum, commonly known as milk thistle, is a medicinal plant belonging to the Asteraceae family. It is one of the most widely used medicinal plants worldwide and is extensively distributed in Algeria due to its richness in bioactive substances. The main objective of this study is to evaluate the antioxidant and antimicrobial potential of the vegetable oil and extracts obtained from its seeds using two extraction methods (maceration and organic solvent extraction). Phytochemical analysis was performed on the various seed extracts of Silybum marianum to identify the main secondary metabolites present. The obtained results highlighted the presence of several groups of bioactive compounds, notably phenolic compounds, flavonoids, tannins, and saponins, whose distribution varied depending on the extraction solvent used. The evaluation of the antimicrobial power of the different extracts and vegetable oil from Silybum marianum seeds was determined using the agar well diffusion method against several microbial strains. The results demonstrated variable efficacy depending on the type of extract and the tested microorganism. Inhibition zones ranged between 6 and 15 mm, with the acetonic extract exhibiting the highest antimicrobial activity, showing a 15 mm diameter against Candida albicans ATCC. Furthermore, distinct MIC (Minimum Inhibitory Concentration) and MBC (Minimum Bactericidal Concentration) values were observed, ranging between 18.75 and 75 \mug/\muL, reflecting distinct levels of antimicrobial activity. Analysis of the MBC/MIC ratio revealed bactericidal effects for some extracts and bacteriostatic effects for others. These results suggest that Silybum marianum seeds contain bioactive compounds capable of inhibiting the growth of microorganisms or eliminating them, thereby confirming their potential as a natural source of antimicrobial agents. To determine the in vitro antioxidant activities of our analyzed extracts, the radical scavenging activity on the DPPH$^\bullet$ radical was evaluated and compared to a reference synthetic antioxidant (ascorbic acid) by determining their efficiency (\text{IC}_{50}). The antioxidant activity of the Silybum marianum extracts evaluated by the DPPH assay showed that the acetonic extract possesses the best free radical scavenging capacity (\text{IC}{50} = 1.90\text{ mg/mL}), whereas the petroleum ether extract displayed the lowest activity (\text{IC}{50} = 48.80\text{ mg/mL}). Ascorbic acid showed a significantly higher activity than all the tested extracts. These results indicate that Silybum marianum seeds constitute a potential source of natural antioxidants, particularly within the acetonic extract.