Medicinal Plant Research 2024, Vol.14, No.1, 11-30 http://hortherbpublisher.com/index.php/mpr 17 The antimicrobial effects of these plants are primarily attributed to their high content of phenolic compounds and essential oils, such as eugenol, terpinen-4-ol, and thymol. These compounds disrupt microbial cell membranes, inhibit enzyme activity, and interfere with microbial DNA synthesis (Salehi et al., 2019; García-Oliveira et al., 2022). The essential oils fromPiper species, for example, contain diverse secondary metabolites that contribute to their broad-spectrum antimicrobial activity (Salehi et al., 2019). Thymol and carvacrol, found in thyme oil, have been shown to interfere with bacterial quorum sensing, thereby inhibiting biofilm formation and microbial communication. Additionally, these compounds can inhibit viral replication by interfering with viral envelope proteins and enzymes essential for viral entry and replication. The antimicrobial properties of these plants make them valuable in the development of natural preservatives for food and pharmaceuticals. They also hold potential as alternative treatments for infections, particularly in the face of increasing antibiotic resistance. The use of Piper species as natural antioxidants and antimicrobial agents in food preservation highlights their practical applications in ensuring food safety and extending shelf life (Salehi et al., 2019). 4.3 Antioxidant effects Aromatic medicinal plants are rich in antioxidants, which have been extensively studied for their ability to neutralize free radicals and prevent oxidative stress. For instance, the essential oils from Thymus algeriensis and Artemisia herba-alba have shown significant free radical scavenging activity and iron reduction capacity (Ouahdani et al., 2021). Similarly, Essential oils from rosemary (Rosmarinus officinalis), lavender (Lavandula angustifolia), and lemon balm (Melissa officinalis) have demonstrated significant antioxidant activity in various assays, such as DPPH, ABTS, and FRAP assays (Koleilat et al., 2017; Gayoso et al., 2018). These studies highlight the capacity of these oils to scavenge free radicals and reduce lipid peroxidation. The antioxidant effects of these plants are mainly due to their ability to neutralize free radicals and reduce oxidative stress. Phenolic compounds and flavonoids found in these plants donate hydrogen atoms or electrons to free radicals, stabilizing them and preventing cellular damage (Hamid et al., 2020; Ouahdani et al., 2021). Such as rosmarinic acid, carnosic acid, and linalool act by donating hydrogen atoms or electrons to neutralize free radicals, thereby preventing cellular damage. Rosmarinic acid, found in rosemary and lemon balm, has been shown to enhance the activity of endogenous antioxidant enzymes, such as superoxide dismutase (SOD) and catalase (Song et al., 2019). Carnosic acid, another potent antioxidant in rosemary, protects cell membranes from oxidative damage by stabilizing lipid structures. The antioxidant properties of aromatic medicinal plants suggest their potential use in preventing and managing oxidative stress-related diseases such as cardiovascular diseases and cancer. Rosemary and lavender oils are incorporated into skincare products for their antioxidant benefits, which help protect the skin from UV damage and premature aging. The potential benefits include improved health outcomes, reduced oxidative damage, and enhanced overall well-being. 5 Mechanisms of Action 5.1 Molecular targets The active ingredients in aromatic medicinal plants interact with specific cellular and molecular targets to exert their pharmacological effects. These targets include receptors, enzymes, ion channels, and signaling molecules. For instance, menthol from peppermint interacts with transient receptor potential (TRP) channels, specifically TRPM8, which is involved in the sensation of cold and pain modulation (Liu et al., 2020). Active compounds from these plants influence various biological pathways. For example, research indicates that eugenol can alleviate inflammatory responses by inhibiting the nuclear factor-kappa B (NF-κB) signaling pathway (Wei et al., 2018). This plays a crucial role in regulating immune and inflammatory responses, capable of reducing the expression of inflammatory factors such as tumor necrosis factor-alpha (TNFα) and interleukin-6 (IL-6), thereby exerting anti-inflammatory effects. Similarly, rosmarinic acid found in rosemary and lemon balm
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