Phytochemical Characterization of Saudi Mint and Its Mediating Effect on the Production of Silver Nanoparticles and Its Antimicrobial and Antioxidant Activities

Abstract

The green synthesis of nanoparticles (NPs) is attracting enormous attention as a new area of study that encompasses the development and discovery of new agents for their utilization in different fields, such as pharmaceuticals and food. Nowadays, the use of plants, particularly medicinal plants, for the creation of NPs has emerged as a safe, ecofriendly, rapid, and simple approach. Therefore, the present study aimed to use the Saudi mint plant as a medicinal plant for the synthesis of silver nanoparticles (AgNPs) and to evaluate the antimicrobial and antioxidant activities of AgNPs compared to mint extract (ME). A phenolic and flavonoid analysis that was conducted by using HPLC indicated the presence of numerous compounds in the ME. Through an HPLC analysis, chlorogenic acid at a concentration of 7144.66 µg/mL was the main detected component in the ME, while catechin, gallic acid, naringenin, ellagic acid, rutin, daidzein, cinnamic acid, and hesperetin were identified in varying concentrations. AgNPs were synthesized by using ME and were confirmed via UV–visible spectroscopy at 412 nm of the maximum absorption. The mean diameter of the synthesized AgNPs was measured by TEM to be 17.77 nm. Spectra obtained by using energy-dispersive X-ray spectroscopy indicated that silver was the main element formation in the created AgNPs. The presence of various functional groups, analyzed by using Fourier transform infrared spectroscopy (FTIR), indicated that the mint extract was responsible for reducing Ag+ to Ag0. The spherical structure of the synthesized AgNPs was confirmed by X-ray diffraction (XRD). Furthermore, the ME showed reduced antimicrobial activity (a zone of inhibition of 30, 24, 27, 29, and 22 mm) compared with the synthesized AgNPs (a zone of inhibition of 33, 25, 30, 32, 32, and 27 mm) against B. subtilis, E. faecalis, E. coli, P. vulgaris, and C. albicans, respectively. The minimum inhibitory concentration of the AgNPs was lower than that of the ME for all of the tested micro-organisms, except for P. vulgaris. The MBC/MIC index suggested that the AgNPs revealed a higher bactericidal effect compared to the ME. The synthesized AgNPs exhibited antioxidant activity with a reduced IC50 (IC50 of 8.73 µg/mL) compared to that of the ME (IC50 of 13.42 µg/mL). These findings demonstrate that ME could be applied as a mediator for AgNPs synthesis and natural antimicrobial and antioxidant agents.