The herb Cymbopogon, a member of the Poaceae family, is also referred to as lemongrass [11]. A perennial grass, lemongrass can reach a height of one meter, and has multiple stiff, green stalks that emerge from short and rhizomatous roots [12]. A perennial aromatic grass known as Cymbopogon citratus is widely grown in the Philippines and Indonesia. It is also cultivated in America and Asia, and, more specifically, in their tropical regions [13]. The plant is mostly an indigenous herb to India, but it is also grown in several tropical and subtropical nations, including in Pakistan [14]. Several species of lemongrass have been found worldwide: Cymbopogon citratus (C. citratus), C. bombycinus, C. refractus, C. nardus, and C. ambiguus.

Due to its commercially valuable essential oils, lemongrass is frequently used in food technology, pharmaceuticals, and traditional treatments. The terpenes, alcohols, ketones, and esters present, as well as the essential oil of lemongrass, differ according to its topographical origin, which affects its chemical makeup. The essential oil that is extracted from lemongrass is mostly found in the leaves of the plant, which are also a great source of it [1]. Up to 5% dry weight of essential oils, primary citral with a distinctive lemonade scent, are present in the leaves [15]. Due to the presence of citral, a cyclic monoterpene, the word “lemon” in its name refers to its distinctive lemon-like aroma [16]. Numerous consumer products contain fragrances made using the oil of lemongrass, such as linalool (1.3%), geranial (39.0%), neral (29.4%), geraniol (1.7%), and myrcene (18.0%) [17]. Myrcene is an anti-bacterial and analgesic compound found in lemongrass, and citronellal, citronellol, and geraniol are its active ingredients. Citral, a volatile oil with a robust lemon aroma, is present in the essential oil. Citral is a mixture of two aldehydes and a stereoisomeric monoterpene; it is used to make perfumes and colored soaps, and synthesizes vitamin A. The geranial with trans isomer nature (40–62%) prevails over the neral with cis isomer nature (25–38%) in citral [1]. Lemongrass has a long history of use in food and beverage recipes, folk medicine, and cosmetics. Due to its alluring scent, Lemongrass is utilized as a flavoring component in many non-food products, such as soaps, perfumes, candles, and insect repellents.

The essential oil of this plant is considered one of the chief volatile oils. Essential oils, perfumes, and volatile plant byproducts have a significant advantage in both the perfume and folk medicine businesses. Many essential oils and the substances that make them up have pharmacological capabilities that act as anti-inflammatory, antioxidant, and anti-cancer agents [18]. Lemongrass essential oil carries great importance, with citral as the main element. The citral content fluctuates from 44.3–91.4% to 79–91.5% in the essential oil [1]. Other important volatile constituents are β-myrcene (11%) and geraniol (1.9%) [19].

Phenolic compounds are a diverse class of plant secondary metabolites, including phenolic acids, flavonoids, stilbenes, lignans, coumarins, curcuminoids, and other polyphenols. Flavonoids are the most abundant phenolic constituents, containing more than ten thousand compounds [5]. The highest concentration of caffeic acid (445.21 ± 32.77 μg/g), p-coumaric acid (393.32 ± 39.56 μg/g), chlorogenic acid (377.65 ± 4.26 μg/g), quinic acid (161.52 ± 17.62 μg/g), and quercetin-3-glucoside (151.35 ± 11.34 μg/g) were reported by Ali et al. [20]. Moreover, catechin, tricin, pyrogallol, diosmin, procyanidin B2, ferulic acid, protocatechuic acid, and p-hydroxybenzoic acid have also been reported in Australian lemongrass. Lutein, apigenin, and their 6,8-glucosides were also reported by Shah et al. [1].

3. Lemongrass and Gut Microbiota