What is lemongrass

Lemongrass (Cymbopogon citratus, Stapf) is a widely distributed and used perennial herb belonging to the Poaceae family ¹⁾. Lemongrass other common names include lemon grass, citronella grass, barbed wire grass, silky heads, cha de Dartigalongue, fever grass, tanglad, hierba Luisa, or gavati chahapati, amongst many others. Lemongrass (Cymbopogon citratus, Stapf) is native to Sri Lanka and South India, and is now widely cultivated in the tropical areas of America and Asia. Lemongrass is a tropical grass in the C₄ grass family that grows in dense clumps that can grow to 6 ft (1.8 m) in height and about 4 ft (1.2 m) in width, with a short rhizome ²⁾. The lemongrass plant (Figure 1) is used as a fragrance and flavoring agent and in folk medicine as an antispasmodic, hypotensive, anticonvulsant, analgesic, antiemetic, antitussive, antirheumatic, antiseptic and treatment for nervous and gastrointestinal disorders and fevers ³⁾. The lemongrass plant is also used as an antibacterial, antidiarrheal, anti-inflammatory, antimutagenic and antioxidant, but the mode of action for the different bioactivities has not been studied in detail ⁴⁾. Lemongrass is a widely used as a culinary herb in tropical countries, especially in Southeast Asia and has been extensively consumed for its medicinal, cosmetic, and nutritional effects for centuries in India. Lemongrass (Cymbopogon citratus) has a subtle citrus flavor, resembling that of lemons (Citrus limon) and can be dried and powdered, or used fresh. Lemongrass is commonly used in teas, soups, and curries. Lemongrass is also suitable for use with poultry, fish, beef, and seafood. Lemongrass is often used as a tea in African countries such as Togo, south eastern Ghana Volta Region and the Democratic Republic of the Congo and Latin American countries such as Mexico.

The lemongrass plant also contains reported phytoconstituents such as flavonoids and phenolic compounds, which consist of luteolin, isoorientin 2’-O-rhamnoside, quercetin, kaempferol and apiginin. Laboratory test tube and animal studies indicate that lemongrass (Cymbopogon citratus) possesses various pharmacological activities such as anti-amoebic, antibacterial, antimalarial, antimutagenicity, antimycobacterial, antioxidants, hypoglycemic, antidiarrheal, antifilarial, antifungal and anti-inflammatory properties ⁵⁾. These results are very encouraging and indicate that lemongrass should be studied more extensively to confirm these results and reveal other potential therapeutic effects.

Lemongrass essential oil is used in aromatherapy. Some of the reported phytoconstituents of lemongrass essential oils are Citral α, Citral β, Nerol Geraniol, Citronellal, Terpinolene, Geranyl acetate, Myrecene and Terpinol Methylheptenone. Lemongrass oil is used as a pesticide and a preservative. Research shows that lemongrass oil has antifungal properties ⁶⁾ and has a wide range of antimicrobial effects such as anti-amebic, antimycobacterial, and antibacterial against both gram-positive and gram-negative organisms ⁷⁾. At a concentration ≤2%, lemongrass essential oil could inhibit the growth of several kinds of microorganisms ⁸⁾. A test tube study by Khongkhunthian et al. ⁹⁾ showed the antimicrobial activity of lemongrass essential oil against periodontal pathogens, especially the reference strains Actinomyces naeslundii and Porphyromonas gingivalis, which were resistant to tetracycline hydrochloride. Lemongrass essential oil in the form of mouthwash was shown to be an effective adjunct to scaling and root planing as a part of nonsurgical therapy for the treatment of gingivitis ¹⁰⁾. The lemongrass essential oil presented remarkable antioxidant and antibacterial activities, which together with its pleasant odor, make this oil a promising natural agent to be used in both the pharmaceutical or food industry ¹¹⁾.

Despite lemongrass essential oil ability to repel some insects, such as mosquitoes, lemongrass oil is commonly used as a “lure” to attract honey bees. Lemongrass works conveniently as well as the pheromone created by the honeybee’s Nasonov gland, also known as attractant pheromones. Because of this, lemongrass oil can be used as a lure when trapping swarms or attempting to draw the attention of hived bees ¹²⁾.

Lemongrass tea possesses various biological properties described in literature, such as anti-inflammatory, antioxidant, anxiolytic, cytotoxic and antinociceptive activities ¹³⁾. However, currently there is no test tube or animal studies available to substantiate these claims on the benefits of lemongrass tea.

Figure 1. Lemongrass plant

Figure 2. Lemongrass

Lemongrass essential oil

Lemongrass contains 1% to 2% essential oil on a dry basis and its chemical composition varies as a function of genetic diversity, habitat, and agronomic treatment of the culture ¹⁴⁾. The volatile oil obtained from the fresh leaves of lemongrass is widely used in the perfume and cosmetic industries ¹⁵⁾. Lemongrass essential oil is mostly composed of monoterpene compounds; citral is a major component, which is a natural mixture of two isomeric acyclic monoterpene aldehydes: cis-isomer neral and trans-isomer geranial ¹⁶⁾. Apart from citral, lemongrass essential oil also consists of myrcene, geraniol, and geranyl acetate ¹⁷⁾. It has been speculated that essential oils without phenolic groups, such as lemongrass oil, cause membrane disruption due to their lipophilic compounds ¹⁸⁾. Lemongrass oil does not only damage the membrane structure through monoterpene diffusion but also facilitates solubility in cell membranes when applied in gaseous form ¹⁹⁾. Furthermore, lemongrass essential oil has antidepressant, antioxidant, antiseptic, astringent, nervine, sedative as well as bactericidal, fungicidal, and generally antimicrobial activity against a diverse range of microorganisms including moulds and yeasts, Gram-positive and negative bacteria ²⁰⁾, ²¹⁾, ²²⁾. However, only a limited number of studies have been performed regarding the application of essential oil in fresh produce ²³⁾, ²⁴⁾ with very promising results.

The components of the essential oils found in lemongrass have a similar pharmacokinetic properties, including absorption, distribution, metabolism, and excretion. They are quickly absorbed following oral, pulmonary, and dermal administration. Based on the published reports, it can also be inferred that, after absorption from the small intestine, some phytochemicals in lemongrass can undergo oxidation, glucuronidation, sulfation, and/or O-methylation. Excretion is through urine, feces and/or expired volatiles. The biotransformation reactions of lemongrass bioactive constituents are essential for its relatively safe consumption and therapeutic applications. The data available so far warrant further studies evaluating lemongrass pharmacokinetics. Reliable pharmacokinetic data in humans would be critical for a better understanding of the the systemic handling of lemongrass.

Several studies have reported antimicrobial activity of lemongrass against fungi and bacteria such as Acinetobacter baumanii, Aeromonas veronii, Aspergillus niger, Bacillus cereus, B. subtilis, Botrytis cinerea, Colletotrichum coccodes, Corynebacterium equii, Cladosporium herbarum, Enterococcus faecalis, Enterobacter aerogenes, Escherichia coli, Fusarium verticillioides, Klebsiella pneumoniae, Proteus vulgaris, Rhizopus stolonifer, Salmonella Typhimurium, Serratia marcesens, and Staphylococcus aureus, either by agar diffusion method or/and broth dilution ²⁵⁾. Contrary to these results, Adegoke and Odesola ²⁶⁾ reported that Fusarium verticillioides growth was not affected when lemongrass oil was added in culture medium. Moreover, the lemongrass essential oil was reported as more effective than synthetic fungicides like Agrosan GN, Dithane M-43, and copper oxychloride ²⁷⁾. Lemongrass oil has also been found effective against Listeria innocua, E. coli and Salmonella Enteritidis in apple, pear and melon juices at 95 °F (35 °C) ²⁸⁾. In the latter study, complete inhibition of the microbial growth was achieved by 2 μL/mL in apple and pear juices and by 5 μL/mL in melon and tryptone soy broth, highlighting the effect of the food matrix. Azarakhsh et al. ²⁹⁾ studied the effects of lemongrass incorporated into alginate-based edible coating for fresh-cut pineapple and reported a significant reduction of the total plate as well as yeast and mold counts of the coated samples during low-temperature storage and a concomitant increase of the shelf life of the product. In another study ³⁰⁾, application of lemongrass in air packaged rocket salads seemed to have a significant fungicidal (kills fungus) effect on growth of yeast-molds at 10–15 °C and bactericidal (kills bacteria) in enterococci populations at all temperatures.

The chemical composition of the lemongrass essential oil varies according to the geographical origin, compounds such as hydrocarbon terpenes, alcohols, ketones, esters and mainly aldehydes have constantly been registered ³¹⁾. The lemongrass essential oil (0.2–0.5%, West Indian lemon grass oil) consists of, mainly, citral ³²⁾. Citral is a mixture of two stereoisomeric monterpene aldehydes; the trans isomer geranial (40–62%) dominates over the cis isomer neral (25–38%) ³³⁾, as shown in Table 1. Chemical structure of the major constituents of lemongrass essential oil (Figure 3) ³⁴⁾.

The antimicrobial effect of lemongrass essential oil is attributed to its citral content, which is the major constituent of the oil (more than 75% by weight) ³⁵⁾. Citral is a natural mixture of isomeric acyclic monoterpene aldehydes geranial (transcitral) and neral (ciscitral) ³⁶⁾. However, both geranial and neral suffer from instabilities resulting from temperature, oxygen, and light that can lead to volatilization, oxidation, or reaction with other formulation ingredients, causing skin irritation ³⁷⁾. Moreover, lemongrass essential oil is characterized by low aqueous solubility ³⁸⁾. These drawbacks limit the practical use of lemongrass essential oil in spite of its various beneficial effects and potent antimicrobial activity.

Table 1. Lemongrass essential oil composition

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Figure 3. Chemical structure of the major constituents of lemongrass essential oil

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Lemongrass and lemongrass oil health benefits

Lemongrass traditional medicine uses

Table 2. Lemongrass traditional medicine uses

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Anti-amebic Effect

The essential oil in broth culture was active on Entamoeba histolytica in a test tube study ⁴²⁾.

Antibacterial Activity

The chromatographic fraction of the lemongrass essential oil in agar plate was active on Bacillus subtilis, Escherichia coli, Staphylococus aureus ⁴³⁾ and Salmonella paratyphi and Shigella flexneri ⁴⁴⁾. These activities are shown in two of the three main components of the oil identified through chromatographic and mass spectrometric methods. While the α-citral (geranial) and β-citral (neral) components individually elicit an antibacterial action on gram-negative and gram-positive organisms, the third component, myrcene, did not show any observable antibacterial activity on its own ⁴⁵⁾. The extract was also active when the volatile oil extract was oxidized via the active oxygen method ⁴⁶⁾. In vitro studies on tomato fruits have indicated complete growth inhibition of Bacillus cinerea and Alternaria arborescens by lemongrass vapors ⁴⁷⁾.

The lemongrass essential oil stands out from the other essential oils (e.g. lavender, juniper berry, eucalypt, rosemary and lemon-eucalypt) in this study ⁴⁸⁾, because lemongrass essential oil demonstrated greatest inhibition of the growth of the bacterial strains tested.

Antidiarrheal Activity

Lemongrass stalk decoction reduced the fecal output in a dose-dependent manner ⁴⁹⁾.

Antifilarial Activity

Fresh lemongrass leaves were active on Setaria digitata ⁵⁰⁾. Setaria is a genus of parasitic roundworms that infect domesticated mammals such as pigs, camels, cattle and horses. Some species also infect wild mammals such as deer and antelope.

Antifungal Activity

Lemon grass oil is active against such dermatophytes such as Trichophyton mentagrophytes, Trichophyton rubrum, Epidermophyton floccosum and Microsporum gypseum ⁵¹⁾ and is among the most active agents against human dermatophytes. Other studies reported that lemon grass oil is active against keratinophilic fungi, 32 ringworm fungi ⁵²⁾ and food storage fungi ⁵³⁾. Lemongrass oil is also effective as a herbicide and as an insecticide because of these naturally occurring antimicrobial effects.

Anti-inflammatory Activity

The hot water extract of the dried leaves administered intragastrically to rats was active when compared with carrageenin-induced pedal edema ⁵⁴⁾.

Antimalarial Activity

The essential oils of Cymbopogon citratus were found to produce 86.6% suppression in the growth of Plsmodium berghei when compared with chloroquine (taking inhibition by chloroquine as 100%) ⁵⁵⁾.

Antimutagenicity

The ethanolic extract of lemon grass extract exhibits an antimutagenic activity in various models ⁵⁶⁾ and retards the growth of fibrosarcoma cells transplanted in mice in association with the prevention of lung metastasis ⁵⁷⁾. The lemongrass plant extract is known to show inhibition on the formation of azoxymethane-induced DNA adducts and aberrant crypt foci in the rat colon ⁵⁸⁾. Inhibitory effects of the lemongrass plant extract on the early phase of hepato-carcinogenesis after initiation with diethylnitrosamine were seen in 344 male Fischer rats ⁵⁹⁾.

Antimycobacterial Activity

The essential oil in agar plate was active on Mycobacterium smegaris ⁶⁰⁾.

Analgesic Effect

The lemongrass essential oil possesses a significant antinociceptive activity. Comparing the results obtained with three different experimental models of pain (hot-plate, acetic acid-induced writhings and formalin test), scientists speculated that the essential oil acts both at the peripheral and at the central levels ⁶¹⁾. Another study examined the effect of citronellal (is one of the main compound responsible for the lemon-scent of many of lemongrass plant) on inflammatory pain induced by different stimuli in mice as well as the involvement of the NO-cGMP-ATP-sensitive K+ channel pathway ⁶²⁾. Citronellal (25, 50 or 100 mg/kg, intraperitoneal.) exhibited a significant reduction of the mechanical nociception induced by tumor necrosis factor α (TNF-α) and carrageenan in all studied doses ⁶³⁾. Citronellal also significantly decreased the mechanical nociception in the dopamine test at doses of 25 and 100 mg/kg, and in the prostaglandin E type 2 (PGE2) test only at higher dose (100 mg/kg). Interestingly, pretreatment with l-NAME or glibenclamide reversed the antinociceptive effect of the Citronellal (100 mg/kg) on PGE2-induced mechanical nociception, suggesting that Citronellal inhibits mechanical nociception through the involvement of NO-cGMP-ATP-sensitive K+ channel pathway. Taken together, these results show the potential of lemongrass citronellal for the treatment of pain ⁶⁴⁾.

Citral is a mixture of two isomers, cis-isomer neral and trans-isomer geranial, and is found in lemongrass oil. The analgesic (antinociceptive) action of citral was demonstrated in mice submitted to different experimental models of acute and chronic nociception ⁶⁵⁾. Pretreatment with citral (25, 100 or 300 mg/kg, orally) inhibited formalin-induced licking in both the neurogenic and inflammatory phases (inhibition of 54% and 65% at 300 mg/kg, respectively); prevented and reduced mechanical hyperalgesia without producing any significant motor dysfunction, with a maximum effect at dose of 100 mg/kg; inhibited the nociceptive response (citral 100 mg/kg) induced by glutamate (inhibition of 49%) and phorbol 12-myristate 13-acetate (PMA; inhibition of 54%); markedly attenuated the pain response (citral 100 mg/kg) induced by N-methyl-d-aspartic acid (NMDA; inhibition of 54%), trans-1-amino-1,3-dicarboxycyclopentane (ACPD; inhibition of 77%), substance P (inhibition of 42%) or cytokine TNF-α (inhibition of 72%); and attenuated the nociception (citral 100 mg/kg) to involve significant activation of serotonergic systems (via 5-HT2A receptor). Together, these results display the potential of citral for the treatment of inflammatory and neuropathic pain ⁶⁶⁾.

Antiprotozoan Activity

A dose-dependent antiprotozoan effect of the essential oil of Cymbopogon citratus could be observed on two strains of Crithida deanei ⁶⁷⁾.

Ascaricidal Activity

The fresh leaf essential oil has an ascaricidal activity ⁶⁸⁾.

Antioxidant Effects

Methanol, MeOH/water extracts, infusion and decoction of lemongrass were shown to have free radical scavenging effects by measuring the bleaching of the 1, 1-diphenyl-2-picryl-hydrazyl (DPPH) radical, scavenging of the superoxide anion and inhibition of the enzyme xanthine oxidase and lipid peroxidation in human erythrocytes ⁶⁹⁾. The lemongrass oil is the one with the best capacity to scavenge the 1, 1-diphenyl-2-picryl-hydrazyl (DPPH) free radicals, presenting an IC50 (concentration providing 50% of inhibition) value of 0.03 ± 0.01 (v/v), that together with a value of antioxidant activity index of 183.37 ± 22.00 allows to classify lemongrass oil as having a very strong antioxidant activity ⁷⁰⁾.

Hypocholesterolemic Effect

The elevated cholesterol concentration was significantly lowered in the animals given the plant extract. This reduction was found to be dose dependent. This result shows that the extract possesses a hypocholestecolemic potential ⁷¹⁾.

Hypoglycemic and Hypolipidemic Effects

A fresh lemongrass leaf aqueous extract administered in normal rats lowered the fasting plasma glucose and total cholesterol, triglycerides, low-density lipoproteins and very low-density lipoprotein dose dependently while raising the plasma high-density lipoprotein level in the same dose-related fashion, but with no effect on the plasma triglyceride levels ⁷²⁾.

Larvicidal Activity

The fresh lemongrass leaf essential oil has a larvicidal activity ⁷³⁾. A methanol-leaf extract of lemongrass shows various degree of repellency and larvicidal effect against a malaria vector, Anopheles arabiensis ⁷⁴⁾. Karunamoorthi K, et al ⁷⁵⁾ also reported the use of essential oil of lemongrass as a repellent. It can provide protection against bites of Anopheles darlingi and Mansonia spp. Morsy et al. ⁷⁶⁾ found solvent extracts of lemongrass have larvicidal activity against third instar larvae of Chrysomyia albiceps. Lemongrass extract is found to reduce a cattle tick, Boophilus microplus, infestation on naturally infested Holstein cows ⁷⁷⁾. Pushpanathan et al ⁷⁸⁾ reported distilled oils extracted from lemongrass had larvicidal and ovicidal activity against the mosquito Culex quinquefasciatus. Jarongsak et al ⁷⁹⁾ reported that essential oil of lemongrass at the rate of 75 µg/cm3 has the highest inhibitory effect, resulting in 97.3±4.7 mortality. The findings of this study ⁸⁰⁾ demonstrated that lemongrass has the potential to be a chemical control agent against house dust mites. Comparing lemongrass and neem, it appears that there was no difference in topical mortalities of D. pteronyssinus from exposure to the concentrations of lemongrass and neem up to 12.50%; lemongrass was more effective than neem at the higher concentrations ⁸¹⁾. Generally, topical mortalities of Dermatophagoides farinae (house dust mites) due to lemongrass were higher than that due to neem. Contact mortalities of lemongrass were always higher than neem against both species of mites ⁸²⁾.

Neurobehavioral Effect

The essential oil was evaluated for sedative/hypnotic activity through pentobarbital sleeping time, anxiolytic activity by elevated plus maze and light/dark box procedures and anticonvulsant activity through seizures induced by pentylenetetrazole and maximal electroshock. The essential oil was effective in increasing the sleeping time, the percentage of entries and time spent in the open arms of the elevated plus maze as well as the time spent in the light compartment of the light/dark box. In addition, the essential oil delayed clonic seizures induced by pentylenetetrazole and blocked the tonic extensions induced by maximal electroshock, indicating the elevation of the seizure threshold and/or blockage of the seizure spread ⁸³⁾.