Phytochemicals are versatile plant secondary metabolites with therapeutic properties. Lemongrass is well-known for its antioxidant, anti-microbial, anti-inflammatory, anti-hypertensive, anti-diabetic, anti-mutagenicity, anxiolytic properties, and for its hypoglycemic and hypolipidemic activities. Therefore, it is widely used in pharmaceuticals, food, feed, and the cosmetics industry. Lemongrass contains phenolic metabolites (including phenolic acids, flavonoids, stilbenes, and lignans), terpenoids, and alkaloids, which are potent bioactive ingredients. Lemongrass is a precious medicinal plant.
1. Introduction
Phytonutrients are considered unique substances which are present naturally in plants, and have been found to carry disease-preventing possibilities which are not only specific, but also powerful. Both kinds of essential and nonessential phytonutrients impart some specific physiological function. They are described as bioactive food mechanisms, with descriptions of their metabolic and physical processes, related goals, and biomarkers [
1]. However, the future need for nutraceuticals will rely on consumer awareness and the association between diet and disorder. Although a useful functional diet and nutraceuticals have a noteworthy role in the improvement and care of human health, in order to stop biotechnologists, regulatory toxicologists, diseases, health professionals, nutritionists, and nutraceutical industrialists should deliberately work in an organized way to create suitable rules to deliver therapeutic methods which can improve the health and welfare of human beings with efficacy, purity, and safety.
Innovative dietary methodologies have improved the developing theory of nutraceutical and designer foods by merging various functional ingredients in order to attain health assistance. Dietary enrichment through nutrification provides significant health benefits due to many plant-based non-nutritive components, i.e., phytoconstituents. Plant-based therapies have, so far, appeared to be an effective strategy to address metabolic and immune dysfunction [
2]. They have been used as therapeutic agents since the earliest times, in both systematized (Unani and Ayurveda) and disorganized (native, folk, tribal) forms. Plants have been well-known to be strong therapeutic agents due to the presence of some nutritional minerals and vitamins, as well as the presence of non-nutritional components, including fibers and active phytochemicals, such as the terpenoids, flavonoids, lignans, sulfides, plant sterols, polyphenolics, coumarins, carotenoids, and saponins [
3,
4,
5]. Plant foods are a vital source of two kinds of mixtures: polyphenolic and phenolic [
6]. These phytochemicals, namely flavonoids and polyphenols, are present in the seeds of fruits and skin, but leaves frequently supply an abundant source of phenolics. Lemongrass is considered to be a potentially beneficial antioxidant source when it is processed under optimal conditions.
2. Phytochemical Constituents of Lemongrass
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.
2.1. Volatile Constituents of Lemongrass
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].
2.2. Phenolic Constituents of Lemongrass
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
It is likely that the desired optimal health and performance of human and animal health can be achieved by modulating the intestinal microbiota and their functions with suitable dietary strategies [
83]. Thus, phytochemicals are potential agents for improving health by establishing a balanced gut ecosystem. Phytochemicals are considered quintessential food and feed additives at the industrial level, since there are no residue or toxin issues. Among the phytochemicals, phytobiotics are used to modulate the gut ecosystem by generating anti-microbial, anti-inflammatory, and antioxidant responses, thus increasing the optimum nutrient absorption in the gut system [
84]. In the intestinal ecosystem, the digestion and absorption of many nutrients occur in the small intestine. At the same time, the cecum is the site that is densely populated with a range of bacteria that are primarily responsible for the fermentation of nutrients not absorbed in the ileum.
Plant extracts and oils have been used for food preservation, pharmaceuticals, alternative medicine, and natural therapies for many years [
85]. The inclusion of dietary lemongrass bioactive compounds contributes to the production and maintenance of gut microflora and digestive functions. Dietary lemongrass promoted the growth of beneficial bacteria while reducing the pathogenic bacterial load, compared to the control groups [
86,
87]. They also found that dietary lemongrass increased the growth of Lactobacillus spp. while inhibiting
Campylobacter spp. and
E. coli in the ileum and cecum. Pinene, a component of lemongrass, possesses a broad spectrum of anti-bacterial activities [
88].
4. Industrial Applications of Lemongrass
It has been claimed that the oil can enhance the flavor of some fish, as well as to flavor wines, sauces, confections, spices, and tea leaves. Lemongrass is a popular culinary herb, used extensively in Southeast Asian nations such as Indonesia, Vietnam, Malaysia, Thailand, Pakistan, and the Philippines. It can be used fresh, powdered, or dried due to its aromatic, lemon-scented qualities. Although the lemongrass pseudostem is challenging to consume, it can be crumbled and added to dishes or grilling rubs. The oil glands which carry aromatic oils in the pseudostem are released if it is bruised or added whole. The lemongrass leaves and stalks have a light lemon flavor, according to Majewska et al. [
93]. Lemongrass is a widely used primary component in Thai and other Asian cuisines, such as Indonesian and Malaysian, due to its mild citrus flavor. This fragrant herb is widely used in Latin American and African nations for curries, poultry, seafood, soups, and teas [
94]. Other nations, such as Thailand, have recently expressed interest in lemongrass. Dried lemongrass leaves are widely used as a lemon-flavored component in herbal teas. In contrast to regular tea, lemongrass is a diuretic and does not alter the body’s biochemistry. According to Nambiar and Matela [
46], Lemongrass is frequently used as the foundation for a well-liked beverage called “Takrai” in Thailand. Additionally, lemongrass is frequently used to prepare marinades, curries, and seafood soups.
Commercial applications for the essential oil of the Cymbopogon genus include its use as an aroma for soap and an ingredient in perfume and palm arosa oil. In the cosmetic industry, several lemongrass products with proprietary formulae combine glycerol, lemongrass, and lemon balm oil. It has been demonstrated that lemongrass essential oil deters insects, making it possible to use it as an insect-repellent lotion [
95]. The cosmetic industry benefits significantly from this oil’s antioxidant properties, as it can be utilized to prevent several skin ailments caused by oxidative stress. Additionally, this substance can be utilized as an anti-aging cream, as oxidative stress is linked to degenerative disorders of chronic nature that accelerate the process of aging (Sara et al. 2006). In the past year, a thorough analysis of the bioactivities of lemongrass that are relevant to its possible aesthetic benefits has also been conducted [
20].
This entry is adapted from the peer-reviewed paper 10.3390/appliedchem2040016