Phytochemical characterisation of Parthenium hysterophorus L. extracts and their antioxidant and antimicrobial activities

Parthenium hysterophorus L. is a noxious and highly invasive weed known for its adverse effects on livestock and human health. Despite its negative impact, the plant possesses notable therapeutic potential. This study investigated the phytochemical composition, conducted quantitative analyses and evaluated the antioxidant and antibacterial activities of various P. hysterophorus extracts. The crude extract of methanol and ethyl acetate of different plant parts was prepared using maceration techniques and antibacterial activity of its crude extract through the agar well diffusion method. The methanol leaves extract exhibited the highest phenolic content (20.38 ± 0.02 mg/g GAE [gallic acid equivalent]), followed by the methanol flower extract (18.99 ± 0.02 mg/g GAE). The ethyl acetate flower extract showed the highest flavonoid content (123.98 ± 5.7 mg/g QE [quercetin equivalent]), while the methanol stems extract contained the most alkaloids (566 ± 6.14 mg/g AAE [ascorbic acid equivalent]). In terms of antioxidant activity, the methanol flower extract demonstrated greater DPPH radical scavenging capacity (IC₅₀ = 482.99 µg/mL) compared to the ethyl acetate leaves extract (IC₅₀ = 637.63 µg/mL). The strongest ABTS scavenging activity was observed in the ethyl acetate leaf extract (IC₅₀ = 79.04 µg/mL) and the methanol flower extract exhibited superior ferric reducing antioxidant power. Antibacterial testing revealed the highest activity against Microbacterium sp. (26.33 ± 0.57 mm at 60 mg/mL) in the ethyl acetate leaf extract. The extract effectiveness against all tested bacterial strains ranked as follows: methanol flower > ethyl acetate leaf > methanol leaf > methanol root > ethyl acetate root > methanol stem. The Ultraviolet–Visible (UV-Vis) spectroscopy and Fourier transform infrared (FTIR) spectroscopy analyses further confirmed the presence of key bioactive compounds. These findings highlight the potential of P. hysterophorus as a source of natural antioxidant and antimicrobial agents, which may serve as alternatives to synthetic compounds.