Mineral composition, content of phenolic compounds and in vitro antioxidant and antibacterial activities of aqueous and organic extracts of the seeds of Peganum harmala L.

Abstract

Peganum harmala L. is well known as a traditional therapy in Morocco. The objective of this study was to determine the mineral composition for the first time, the chemical profile and the antioxidant and antibacterial activities of Peganum harmala L. seeds. The aqueous extracts were prepared by three modalities: decoction, infusion and maceration, while the organic extracts methanolic, ethyl acetate, chloroformic and petroleum ether were obtained by Soxhlet, and the methanolic macerated extract by cold maceration. Phytochemical screening was conducted on both the seed powder and the extracts prepared from it. Similarly, the content of phenolic and flavonoid products was determined. In addition, antioxidant activity was evaluated by five different methods: H2O2, DPPH, ABTS, FRAP and PR. The correlation between chemical composition and antioxidant activity was evaluated using PCA. Finally, the antibacterial activity by the disc diffusion method, minimal inhibitory (MIC) and bactericidal (MBC) concentrations of the organic extracts were evaluated against six gram-positive and gram-negative pathogenic bacteria. The results obtained showed that the seeds of Peganum harmala L. are characterized by a particularly high content of potassium (111.6200 mg/l) and iron (64.4080 mg/l). Phytochemical screening revealed the presence of alkaloids, flavonoids and saponins. The methanolic macerated extract is the richest in polyphenol (94.37 ± 0.62 µg GAE/mg E) and the ethyl acetate extract in flavonoids (366.13 ± 1.88 µg QE/mg E). Petroleum ether and aqueous infusion extracts have the strongest percentages of H2O2 inhibition (21.02±1.13% and 21.02±1.07%) which is greater than that of ascorbic acid (14.35±0.002%) with a significant difference. Ethyl acetate extract showed the best activity by the DPPH (IC50= 146.20±13.41 µg/ml) and ABTS (49.84±1.15 µg TE/mg E) tests, methanolic macerate by the FRAP test (68.04±1.52 µg TE/mg E) and the methanolic extract by the reducing power test (61.77±1.41 µg AAE/mg E). The antioxidant activity determined by DPPH, ABTS, FRAP and PR showed a positive correlation between the 4 tests, and with the content of polyphenols and flavonoids with the exception of the activity measured by H2O2, where the correlation is negative. The study of the antibacterial effect showed that the four organic extracts: methanolic, methanolic macerate, ethyl acetate and chloroform have an inhibitory effect on six microorganisms with inhibition zones that vary between 8 ± 0.00 and 23.7 ± 2.60 mm, Pseudomonas aeruginosa is the most sensitive strain with an inhibition zone diameter of 23.7 ± 2.60 mm with the methanolic macerate extract, while the petroleum ether extract showed no effect. In addition, the MICs obtained range from 1.56 to 12.5 mg/ml and the MBCs vary from 1.56 for Proteus mirabilis with ethyl acetate extract to 100 mg/ml. In conclusion, polar organic extracts of Peganum harmala L. are a promising source of antioxidants and antibacterial agents and Principal Component Analysis (PCA) showed that the four methods ABTS, DPPH, FRAP and PR are correlated with each other and that the antioxidant capacity of the extracts is related to their content of total polyphenols and flavonoids. This activity can also be related to the mineral composition of the plant, such as copper, manganese, zinc, which are considered an important class of antioxidants.