HerbalEGram: Volume 14, Issue 10, October 2017

Editor’s Note: Each month, HerbalEGram highlights a conventional food and briefly explores its history, traditional uses, nutritional profile, and modern medicinal research. We also feature a nutritious recipe for an easy-to-prepare dish with each article to encourage readers to experience the extensive benefits of these whole foods. With this series, we hope our readers will gain a new appreciation for the foods they see at the supermarket and frequently include in their diets.

The basic materials for this series were compiled by dietetic interns from Texas State University in San Marcos and the University of Texas at Austin through the American Botanical Council’s (ABC’s) Dietetic Internship Program, led by ABC Education Coordinator Jenny Perez. We would like to acknowledge Perez, ABC Special Projects Director Gayle Engels, and ABC Chief Science Officer Stefan Gafner, PhD, for their contributions to this project.

By Hannah Bauman^a and Maegan Davis^b

^a HerbalGram Associate Editor

^b ABC Dietetics Intern (Texas State, 2016)

Overview

West Indian lemongrass (Cymbopogon citratus, Poaceae) is an aromatic tropical perennial with long, slender, light green leaves that grow in groups with bulbous and fibrous stems at the base of the plant.^1-3 The grass can grow from two to six feet tall, and its leaves are approximately one inch wide with slightly toothed, saw-like margins.² West Indian lemongrass likely originated from India, Malaysia, or Sri Lanka.^1,2,4,5 It is now cultivated in tropical and subtropical countries.⁴ The largest exporter of lemongrass leaves and stalks is Guatemala,⁵ while India is the largest producer of lemongrass essential oil, 80% of which is exported annually.⁶ Lemongrass grows well in warm and humid areas with plenty of sunshine and moisture.⁴ The leaves and fleshy part of the stem are used for flavoring teas and broths in many Asian cuisines, and its essential oil is used in cosmetics and food preservation.^1-3

Phytochemicals and Constituents

West Indian lemongrass contains an array of electrolytes and minerals, including potassium, sodium, calcium, copper, magnesium, manganese, selenium, phosphorus, iron, and zinc. It also contains vitamin C, as well as the B vitamins niacin, pyridoxine, riboflavin, and folate.³ It has high carbohydrate content, and its leaves are high in crude fiber.⁴

The bioactive compounds in lemongrass include saponins, tannins, flavonoids, phenols, and alkaloids, as well as its essential or volatile oil compounds: monoterpenes and sesquiterpenes, including aldehydes, alcohols, and esters.⁷ The essential oil has shown antimicrobial, anti-inflammatory, cytotoxic, and antioxidant activities. The strong scent of lemongrass is attributed to citral, a compound that accounts for 65-85% of the essential oil. The quick metabolism and excretion rate of citral results in no significant bioaccumulation of the compound.⁷ In cultured cells, citral has been shown to increase the activity of the enzyme glutathione S-transferase, which is involved in the elimination of xenobiotics (i.e., molecules that are foreign to the human body⁷), but it is not clear to what extent, if any, this experimental research might relate to human metabolism of preparations containing lemongrass essential oil.

Lemongrass essential oil also contains linalool, menthol, eugenol, geraniol, myrcene, and cinnamic aldehyde — all of which have antibacterial effects. Among these, cinnamic aldehyde possesses the greatest antimicrobial activity, while linalool provides the strongest antibacterial activity. Citral, geraniol, and myrcene exhibit the strongest antifungal activity.⁷

Historical and Commercial Uses

Traditionally, lemongrass has been used as a food ingredient, in cosmetics, and in folk medicine. Lemongrass is also used as a flavoring for non-alcoholic beverages, prepared dishes, and baked goods, and the essential oil has been used to preserve food due to its antimicrobial activities.³ Lemongrass decoction is a popular beverage served hot or cold in Peru, Brazil, Cuba, and India.^3,4 In Thailand, lemongrass is known as takrai and commonly is used in Thai dishes such as curries, soups such as tom kha, and in marinades for meat. In Vietnam, lemongrass is added to salads, and in Java, it is used to prepare a sherbet.⁴ Its aromatic oil is prized in soaps, perfumes, candles, and mosquito or insect repellents.

Lemongrass has a history of medicinal use among several cultures worldwide for a variety of conditions including digestive disorders, fevers, menstrual disorders, joint pain, inflammation, and nervous conditions.⁴ In the Philippines, lemongrass tea is used to soothe stress, alleviate colds, fevers, and gastrointestinal distress, and manage pain and arthritis. In the Paraná state in southern Brazil, lemongrass is a preferred herbal medicine for pain relief and to sedate or calm the central nervous system. In India, Cuba, Indonesia, and Brazil, lemongrass infusions/teas are used to treat bladder disorders (including inflammatory conditions of the urinary tract), urinary incontinence, and kidney stones.⁷ In Nigeria, hot water extracts of lemongrass are used to treat hypertension, obesity, and diabetes mellitus. It is also used there in the treatment of malaria, to lower fevers, and to kill protozoa.

Modern Research

Lemongrass has traditional uses as an antibacterial, antifungal, antiprotozoal, anxiolytic, and antioxidant. Though there are few human clinical trials at the time of this writing (September 2017), modern pharmacological research has investigated lemongrass preparations for a variety of conditions and uses: to prevent platelet aggregation, treat malaria, alleviate digestive upset, and treat metabolic disorders including dyslipidemia, as well as colds, flu, and pneumonia.⁷ As is the case with most botanical materials, both in vitro and in vivo studies on lemongrass suggest that its reported therapeutic properties are most likely the result of a synergy of many compounds rather than a single compound.

Antimicrobial, Antifungal, and Antiviral Properties

The essential oils derived from the steam-distillation of lemongrass leaves have shown activity against 20 different bacteria (including Escherichia coli, Klebsiella pneumoniae, Proteus vulgaris, Enterobacter faecalis, Salmonella, and Shigella), seven different yeasts (including Candida albicans), and 15 different fungi (including common food-storage fungi).^7-9

In vitro studies have shown that lemongrass essential oil can be more effective than antibiotics against a certain pathogenic bacteria. Lemongrass oil appears to increase the range of action of phenoxyethanol (a preservative for pharmaceuticals, cosmetics, and home care products) against E. coli, Staphylococcus aureus, and Pseudomonas aeruginosa.⁷ As antibiotic resistance becomes more common, the use of lemongrass essential oil shows promise in the control of a wide range of bacterial infections.⁸

Citral, linalool, myrcene, and geraniol, which are present in lemongrass essential oil, have antifungal properties. In vitro studies with Candida albicans demonstrate linalool’s ability to reduce cell size and cause abnormal germination, which inhibits the ability of Candida species to replicate efficiently. Citral appears to inhibit both mycelial and yeast-form growth of C. albicans. These effects could lead to the reduction and potential inhibition of the biofilm formation necessary for Candida species to thrive.⁷

A 0.1% concentration of lemongrass oil completely inhibited herpes simplex virus-1 replication in vitro.⁷ In a small, randomized, controlled trial, lemongrass tea was found to effectively treat oral thrush (a fungal infection of the mucous membranes of the mouth that is caused by Candida species) in patients with human immunodeficiency virus (HIV) and acquired immune deficiency syndrome (AIDS).¹⁰

Antioxidant Properties

Lemongrass is a good source of protective antioxidant compounds such as vitamin C and flavonoids.⁷ In the food industry, there has been increased interest in natural methods of food preservation, and essential oils derived from plants can be used to inhibit microorganisms that cause food spoilage and shorten the shelf-life of food products.⁹ The strong inhibitory effects of lemongrass essential oil against a wide variety of pathogens, combined with its antioxidant potential, make it a potential food preservative.^7,9

An in vitro study demonstrated the protective effects of lemongrass against hydrogen peroxide-induced oxidative stress and liver damage. Lemongrass intake was associated with a decrease in hydrogen peroxide-induced elevation of liver enzymes and a reduction of oxidative stress-induced pathological changes.⁷ In a rat study, citral isolated from lemongrass was shown to enhance detoxification in the liver by inducing glutathione S-transferase, an enzyme involved in the detoxification process.

Gastroprotective Properties

In another rat study, lemongrass was investigated for its gastroprotective benefits. A lemongrass extract was found to have protective effects against stomach lesions.¹¹ A similar study investigated the effects of lemongrass essential oil against damage caused by ethanol and aspirin exposure.¹² The essential oil showed a protective effect against ethanol- and aspirin-induced lesions. For people who regularly consume alcohol or use non-steroidal anti-inflammatory drugs (NSAIDs), these results suggest that lemongrass oil may help protect the lining of the stomach, which can be damaged by use of NSAIDs and alcohol.

Anxiolytic Properties

In aromatherapy, lemongrass essential oil often is used as a mood enhancer.⁷ While some studies support lemongrass’s sedative and anxiety-reducing effects on the central nervous system, these effects have not been consistently demonstrated.

Studies on lemongrass aqueous root extract and methanolic leaf extract have demonstrated anxiolytic effects.^13,14 These effects could be related to the flavonoids, alkaloids, and terpenoids present in lemongrass extracts, all of which have been associated, in other plant extracts, with reduced anxiety.¹⁴

Empirical studies show that inhalation of lemongrass essential oil has an inhibitory effect on the central nervous system by increasing levels of the neurotransmitter gamma-aminobutyric acid (GABA) in the brain. This suggests that the anxiolytic effects of lemongrass essential oils may be mediated by acting upon the GABA-benzodiazepine interaction complex.^7,15

Neuropharmacological Properties

Lemongrass water extracts (teas or broths) contain neuroprotective nutrients such as zinc, magnesium, and folate, which are associated with improved memory, concentration, and information processing.⁷ In a mouse study, lemongrass essential oil was found to be three times more effective than sodium thiopental, a common anesthetic, at prolonging sleep. Additionally, lemongrass essential oil has been shown to raise the seizure threshold and reduce convulsive episodes in rats and should be further investigated for use in managing epilepsy in humans.

Hypoglycemic and Hyperlipidemic Properties

A rat study examined the effects of oral intake of three different doses of lemongrass tea on weight reduction, serum cholesterol levels, and fasting plasma glucose.¹⁶ Researchers observed a dose-dependent reduction in weight, with the higher dose leading to a greater weight reduction, and the maintenance of low blood glucose levels. Additionally, this study reported a significant, dose-dependent reduction in levels of total cholesterol, low-density lipoprotein (LDL) cholesterol, and very low-density lipoprotein (VLDL) cholesterol, while high-density lipoprotein (HDL) cholesterol increased significantly. Levels of triglycerides were unaffected.

In a small open-label human clinical trial, effects of lemongrass tea on 31 patients with hypertension were observed. Participants were given a lemongrass infusion twice daily for 16 weeks. Lemongrass tea intake had a significant effect on reducing blood pressure, but no significant effect on heart rate or other recorded study parameters.⁴

Consumer Considerations

There is conflicting and inconclusive evidence regarding the toxicity of lemongrass. Citral has been found to cause skin irritation such as contact dermatitis.^3,17 In the European Union (EU), citral is one of 26 likely allergens identified by the EU Cosmetics Regulation, and all cosmetic and home care products that contain lemongrass oil or extract must state this on the label.¹⁸ Additionally, citral appears to induce hepatic cytochrome P450 activity, potentially causing prescription drugs and medications to be metabolized more quickly, which may cause adverse effects, depending on the medication. There are also reports that citral and myrcene may adversely affect embryos.^3,17 Potential adverse effects on the kidneys are inconclusive, but high doses or prolonged use of citral (and, by extension, lemongrass) could be toxic to the kidneys. Liver studies also have been conflicting and inconclusive. It is recommended that individuals with kidney damage or liver disease, who are pregnant or lactating, and children under the age of six should be cautious when using lemongrass.^3,17

Lemongrass is a widely cultivated tropical perennial that has been evaluated for its ability to improve soil stability and eliminate potentially harmful substances from soils and farm field runoff.⁶ This wastewater often contains salts, pathogens, heavy metals, and other pollutants that may contaminate the food web, posing serious health threats to human and animal health. The use of fibrous-rooted plants like lemongrass and other large, clumping members of the grass family to sequester harmful chemicals and prevent them from entering waterways is a key practice in bioremediation. Agricultural studies report that lemongrass and other aromatic crops can be grown in soils contaminated by heavy metals without resulting in a significant transfer from the soil into the essential oil fraction of the plant. The heat required for steam distillation kills pathogens and reduces the transfer or uptake of any heavy metals into the essential oil product. Lemongrass grown on contaminated sites produces essential oils that are deemed safe for therapeutic use and may be appropriate for most non-edible purposes such as cosmetics and perfumes.

Nutrient Profile¹⁹

Macronutrient Profile: (Per 1 ounce [approx. 28 grams] fresh lemongrass)

28 calories
1 g protein
7 g carbohydrate
0 g fat

Secondary Metabolites: (Per 1 ounce [approx. 28 grams] fresh lemongrass)

Excellent source of:

Manganese: 1.5 mg (75% DV)

Very good source of:

Iron: 2.3 mg (12.8% DV)

Good source of:

Potassium: 202 mg (5.7% DV)
Folate: 22 mcg (5.5% DV)

Also provides:

Magnesium: 16.8 mg (4.2% DV)
Phosphorus: 28.3 mg (2.9% DV)
Riboflavin: 0.04 mg (2.4% DV)
Calcium: 18.2 mg (1.8% DV)
Niacin: 0.3 mg (1.5% DV)
Thiamin: 0.02 mg (1.3% DV)
Vitamin C: 0.7 mg (1.2% DV)
Vitamin B6: 0.02 mg (1% DV)

DV = Daily Value as established by the US Food and Drug Administration, based on a 2,000-calorie diet.

Recipe: Green Curry Paste

Courtesy of Bon Appétit²⁰

For more information on the beneficial properties of shallot,²¹ ginger,²² coriander,²³ and cumin,²⁴ please see their respective Food as Medicine articles.

Ingredients:

• 2 lemongrass stalks, tough outer layers removed
• 12 serrano chiles, seeds removed and roughly chopped
• 1 large shallot, peeled and chopped
• 4 garlic cloves, peeled
• 3-inch piece of fresh ginger, peeled and thinly sliced
• 2-inch piece of fresh turmeric, peeled and chopped; or 1 teaspoon dried turmeric
• 1 makrut lime leaf, very finely chopped (optional)
• 1 teaspoon each ground coriander, ground cumin, kosher salt, and sugar

Directions:

1. Grate the softer inner core of the lemongrass stalks into a food processor or mortar bowl. Add remaining ingredients and process or pound with the pestle until a smooth paste forms.
2. Curry paste can be frozen for up to three months. Combine 1-2 tablespoons with one can of coconut milk for the base of a curry dish.

All photo credits: ©2017 Steven Foster

References

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4. Nambiar V, Matela H. Potential functions of lemon grass (Cymbopogon citratus) in health and disease. International Journal of Pharmaceutical & Biological Archives. 2012;3(5):1035-1043.
5. Department of Agriculture, Forestry, and Fisheries. Lemongrass Production. Pretoria, South Africa: Department of Agriculture, Forestry, and Fisheries; 2012.
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