Lemongrass as a multipurpose aromatic crop: Agronomic management, bioactive compounds and industrial significance

Introduction

The genus Cymbopogon belongs to the Poaceae family, is grown as perennial herb, known for their essential oil having pharmacological as well as therapeutic activities, and is widespread in its distribution throughout tropical and subtropical regions of world (Nambair and Mehta; Ekpenyong et al.). Lemongrass essential oil is a yellow coloured viscous liquid, volatile and chemically lipophilic mixture of secondary metabolites, mostly consisting of monoterpenes, sesquiterpenes and phenylpropanoids. Citral is the main constituent of oil and is made up of geranial and neral isomers; it acts as starting material for synthesis of alpha ionone, beta ionone and beta-carotene. The alpha ionone is used in cosmetics, perfumes, and flavours while beta ionone is used for synthesis of vitamin A. Lemongrass oil has promising antimicrobial, antiinflammatory and analgesic, antioxidant activity, antispasmodic, antipyretic, diuretic and sedative values (Fokom et al., 2019) [7] . It is used as spice due to its good taste appeal and not only used as flavouring agent but also utilized in food preservation and food processing, because of antioxidant, antibacterial, antimycotoxin and antibiofilm action (Boukhatem et al.). The oil also exhibits insecticidal, larvicidal, pesticidal and antifeedant properties (Barbosa et al.). The explosive demand of essential oil for industrial uses and therapeutic potential necessitates getting above average production.

Area

More than 60000 hectares area is under cultivation of aromatic grasses in India distributed in different states viz., Madhya Pradesh, Gujarat, Karnataka, Assam, Kerala, Maharashtra, Uttar Pradesh and Andhra Pradesh (Husain; Padalia et al.).

Species

There are more than 140 species in the genus Cymbopogon (Kumari et al), out of which 45 are grown in India, and lemongrass is commercially important for the production of essential oil (Hassan et al). The Cymbopogon spp. have a unique character, that they can be cultivated in different types of soils even with less fertile status of the land and have good adaptability to diverse agro-climatic conditions. The most commonly cultivated and conomic species of [35] .

Economic importance

The essential oil is obtained through distillation of the leaves and flowering tops of lemongrass. Its intensely lemon like aroma is attributed to the high concentration of citral, which constitutes more than 75% of the oil. Owing to this distinctive fragrance, the oil is extensively utilized for imparting scent to soaps, detergents, and insect repellent formulations. Nevertheless, its principal commercial importance lies in serving as a primary source of citral, which is widely employed in perfumery, cosmetic formulations, and beverage industries, and also functions as a key precursor in the synthesis of ionones that are subsequently used in the production of vitamin A. The citral rich oil further exhibits notable germicidal, therapeutic, and flavour enhancing properties.

Botanical description

Lemongrass is a highly adaptable and multipurpose grass species that develops in thick, compact clumps arising from short rhizomes, attaining heights of up to 6 ft (1.8 m) and spreading approximately 4 ft (1.2 m) in width. The foliage consists of band shaped leaves measuring nearly 3 ft in length, gracefully arching with distinctly drooping tips. Individual leaves are about 0.5 to 1 inch in width. The bluish green, evergreen foliage releases a pronounced citrus fragrance when crushed (Alzawqari, M. H., et al., 2016) [1] .

 Leaf arrangement: Most leaves arise directly from the soil surface without the presence of an evident stem.  Leaf type: simple  Leaf margin: entire Leaf shape: linear Leaf venation: parallel  Leaf type and persistence: fragrant  Leaf blade length: 18 to 36 inches  Leaf color: Green fall characteristic: showy flowers Lemongrass is a cultivated variety and usually does not produce flowers or well developed flowering panicles (Ross, 2001) [18] .

Inflorescence The inflorescence attains a length of about [7] . To achieve maximum oil yield, supplementary irrigation is recommended, with an ideal daytime temperature of 25 to 30°C and a nighttime temperature of 0 °C. Although plants can withstand temperatures exceeding 30 °C for short durations, a marked reduction in oil content is observed under such conditions. The species is hardy in nature and capable of resisting drought stress. Plant height during the rainy season was recorded as the lowest, and similar reductions were not observed during the second harvest. Further compounds detected include cis and α-p-mentha-2, pmentha-2, 8-dien-1-ol, methyl thymol ether, α-murolen, myrtenal, phellandrene, myrtenal, alpha-pineol, αpineol, β-thuj,-2,-en-4-ol, verbenone, β-ylangen, α-pineol, and cis-peperitol. The primary constituents identified in the leaves of C. citratus reveal notable variation in the proportions of geraniol and geranyl acetate during different stages of leaf development. In essential oil extracted on the tenth day following leaf emergence, geraniol and geranyl acetate were recorded at approximately 59% and 33%, respectively. In addition, two dominant components, Piperidone at 54.36% and Phellandrene at 30.86%, have been reported as key constituents of the essential oil. The base oil of C. citratus also contains saponins, tannins, anthraquinones, alcohols, phenols, and flavonoids. The major chemical groups detected in the essential oil include terpenes, alcohols, ketones, aldehydes, and esters. Significant individual compounds comprise citral α, citral β, geraniol, nerol, citronellal, geranyl acetate, terpinolene, myrcene, and terpinole, while flavonoid constituents such as luteolin, orientin 2-Orhamnoside, quercetin, kaempferol, and apigenin have also been identified (Majewska et al., 2019) [9] . [22,23,24,25,26,5,27,28,29]

Propagation By seeds

In Kerala State, the most popular technique is based on seeds. November to December is when the crop flowers, and January to February is when the seeds are gathered. The plants are not harvested in order to collect the seeds since plants that are regularly harvested produce fewer seeds. A healthy plant often yields 100-200 g of seeds. The entire inflorescence is clipped and spread out in the sun to dry for two to three days at the time of seed collecting. The seeds are then dried in the kiln once more after being beaten. Ultimately, these are kept in gunny sacks.

Longer storage times cause the seeds to lose their viability.

Raising of seedlings in nursery

It is advantageous to transplant seedlings to expand the plantation anytime a steady supply of water is available. Direct seeding has been found to be less effective than transplanting seedlings grown in nurseries. The seeds are manually sown on a thin layer of soil on constructed raised beds that are one to one and a half meters wide at the beginning of the monsoon. 3-4 kilogram of seed per hectare is recommended. It is recommended that the bed be watered as soon as possible after seeding, and that the soil be kept adequately moist. After 5-6 days of germination, the seedlings are prepared for transplantation 60 days later.

By rooted slip

To obtain superior oil quality and higher yield, cultivation of lemongrass is recommended through vegetative propagation using slips prepared from healthy, well established clumps. The upper portions of the clumps are trimmed to a height of 20 to 25 cm above the root level. Subsequently, the clumps are carefully separated into individual slips, and the lower brown sheath is removed in order to expose the young and actively growing roots prior to planting.

Irrigation

The recently developed varieties of lemongrass possess specific water requirements to achieve optimum yield. Under the climatic conditions of northern India, approximately 4 to 6 irrigations are provided during the summer period extending from February to June. In situations where rainfall distribution is irregular, irrigation is applied at intervals of 3 days during the initial month following planting, and thereafter at intervals of 7 to 10 days. Once the crop becomes well established, the irrigation schedule is modified in accordance with the soil's water holding capacity and the prevailing weather conditions.

Intercultural operation

The crop field is maintained free from weeds during the first 3 to 4 months after planting to ensure proper establishment and growth. In addition, weeding combined with hoeing operations are carried out up to one month after each harvest. Typically, 2 to 3 weedings are required annually to sustain effective weed management. In crops planted in rows, intercultural operations may be performed using a tractor drawn cultivator or by manual hoeing. The residual waste obtained after distillation is utilized as an organic mulch at the rate of 3 tonnes/ha, which has been observed to effectively suppress weed growth in the field.

Regarding chemical control measures, the application of Diuron at 1.5 kg ai/ha and Oxyfluorfen at 0.5 kg ai/ha has proven effective in managing weeds. Once fully established, lemongrass itself contributes to suppressing weed growth by providing ground cover.

Manure and fertilizers

Nitrogen, phosphorus and potassium @150:60:40 is required per ha per year. Entire amount of phosphorus and potassium is applied at the time of last ploughingin 1 st year and in subsequent year after the summer harvesting. Nitrogen is appliedin splits thrice per harvest, under non-irrigated condition quantity of fertilizer will be reduced.

Harvesting yield

Lemongrass undergoes flowering during the winter season. The initial harvest is typically secured 4 to 6 months after the transplantation of seedlings. Thereafter, successive harvests are carried out at intervals of 60 to 70 days, with the exact timing influenced by soil fertility status and prevailing seasonal conditions. Under standard cultivation practices, three harvests can be achieved in the first year, while 3 to 4 harvests are feasible in the following years depending upon the management strategies adopted. Harvesting is performed manually using sickles, cutting the plants approximately 10 cm above the ground level, after which the harvested material is left in the field to wilt prior to its transport to the distillation unit.

Yield

The economic lifespan of a lemongrass plantation generally extends for about 3 to 4 years, depending on prevailing soil characteristics and climatic conditions. Oil production remains relatively low during the first year of cultivation, increases noticeably in the second year, and reaches its peak in the third year, after which a gradual decline in yield is observed. On average, 25 to 30 tonnes of fresh herbage per hectare per year are obtained from 4 to 6 harvests, resulting in an approximate oil recovery of 80 kg. When cultivated under irrigated conditions using newly developed varieties, oil yields ranging from 100 to 150 kg/ha have been reported. The freshly harvested herb contains about 0.3% essential oil on average, and the thicker stems are separated prior to distillation because they do not contain oil.

Distillation method

Distillation techniques involves introducing the desired part of the plant to steam or boiling water and the vapour is made to flow along the network of tubes which forms the condenser from which the oil drops are collected. There are three different systems viz., hydro-distillation, hydrosteam distillation and steam distillation.

Crop Economics: On the basis of 5 years [30] Cauvery

Cymbopogon flexuosus

Phenotypic recurrent selection

Requires high soil moisture and is evolved for river valley tracts of Indian Plains Patra et al (2005) [31] Nima Cymbopogon flexuosus Half sib seed followed by clonal selection Indian Plains Anonymous ( 2003) Anonymous ( 2003) [32] OD-19

Cymbopogon flexuosus

Clonal selection Adapted to a wide range of soil and climatic condition. much suited for rained cultivation Kumar et al (

CIM-Suwarna Cymbopogon khasianus Clonal selection Drought prone areas and marginal lands Lal et al (2010) [33]

CIM-Shikar

Cymbopogon flexuosus Recurrent selection High yielding cultivar (>20% Krishna) Anonymous, (2016) [34]

CKP-25

Cymbopogon flexuosus Hybridization Grows well in northern plains Rao and Sobti, (1991) [35] CIM-Atal Cymbopogon flexuosus Selection Geraniol rich (80-85%) grows well in tropical and subtropical region Kulkarni et al (2020) [36] Potential for biofuel production

The southeastern United States holds potential for ethanol production from lemongrass owing to its substantial biomass yield. Compared with other lignocellulosic crops currently under investigation in the United States, lemongrass presents a distinct advantage because, in addition to biomass, it yields essential oil, a high value natural product that may help compensate for production expenses. Crops cultivated exclusively for biomass may therefore offer fewer economic benefits than those capable of serving dual purposes such as biofuel and essential oil production. In the present investigation, lemongrass biomass yields ranged from 7,500 to 25,900 kg/ha at Verona and from 8,036 to 12,593 kg/ha at Poplarville. In contrast, an evaluation of 39 experiments assessing the production potential of switch grass (Panicum virgatum L.) in the United States reported mean yields of 8,700 ± 4,200 kg/ha for upland ecotypes and 12,900 ± 5,900 kg/ha for lowland ecotypes (Wullschleger et al). While switch grass intended for ethanol production has largely been examined under rain fed conditions, the lemongrass evaluated in this study was cultivated under irrigation. Although switch grass is generally regarded as more tolerant to diverse environmental conditions than lemongrass, the latter offers specific advantages for the southeastern United States, including the generation of a valuable natural product and the extraction of essential oil through a process that effectively subjects the biomass to thermal treatment.

Steam distillation of lemongrass essential oil, which essentially involves exposing the biomass to hot steam for approximately 2 hours, may help reduce biomass recalcitrance as described by Himmel et al. (2007) [37] . As a result of this pretreatment, lemongrass biomass may be more amenable to ethanol conversion compared with biomass from other species that have not undergone hot steam processing. The production of essential oil from lemongrass may also contribute to ongoing discussions concerning the economic, agronomic, and environmental implications of large-scale biofuel crop cultivation. Lemongrass biomass exhibits structural uniformity because the plants develop as rosettes bearing elongated leaves. In the southeastern United States, lemongrass did not produce stems or inflorescences, resulting in a homogeneous biomass composed entirely of leaves, a characteristic that may further facilitate bioethanol production. Currently, essential oil of lemongrass is imported from India to satisfy domestic demand, as commercial production is not established within the United States. Cultivating lemongrass in the Southeast United States for both biofuel and essential oil purposes could provide farmers with an additional income source. Moreover, the production of lemongrass oil may encourage regional value-added processing industries centered on essential oil extraction, thereby strengthening the overall economic sustainability of the region.

Conclusion

The aromatic grass Cymbopogon sp. contains numerous bioactive constituents that exhibit extensive medicinal potential. Its utility has already been established in the fragrance and cosmetic industries. Looking ahead, the therapeutic attributes and essential oil of lemongrass may find broader applications within herbal medicine. The plant is capable of assisting in the management of infectious conditions affecting the respiratory tract and contributes to the prevention of gum disease and periodontitis through the elimination of pathogenic bacteria from the oral cavity. The antibacterial efficacy of Cymbopogon citratus is well documented. Moreover, C. citratus demonstrates strong antioxidant activity through effective free radical scavenging and possesses high total flavonoid and total phenolic contents. The species exhibits antifungal, antibacterial, antinociceptive, and cardioprotective activities. In addition, C. citratus is reported to have sedative, antithetical, and vasorelaxant properties. Medicinal plants play an essential role in sustaining human health, and there has been increasing scientific attention toward the pharmacological assessment of plants used in traditional Indian systems of medicine. Owing to their extensive use in traditional healing practices and culinary applications, along with their economic significance, lemongrass essential oils have attracted considerable interest.

A comprehensive phytochemical and pharmacological investigation is essential to further explore the therapeutic potential of this remarkable plant. The renewed focus on natural products derived from lemongrass may pave the way for expanded pharmacological applications, thereby supporting clinical research initiatives and facilitating the development of novel therapeutic agents.

Future scope

Numerous species of lemongrass are cultivated all over the world; the molecular diversity analysis of lemongrass will be the focus of future research. To guarantee that all of the oil's components are available, the methods currently used for extracting essential oils can be enhanced. Lemongrass oil has a number of uses that should be investigated

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