Citrus hystrix DC
Citrus balincolong (Yu.Tanaka) Yu.Tanaka, Citrus boholensis (Wester) Yu.Tanaka, Citrus celebica Koord., Citrus combara Raf., Citrus echinata St.-Lag. [Illegitimate], Citrus hyalopulpa Yu.Tanaka, Citrus kerrii (Swingle) Yu.Tanakam, Citrus kerrii (Swingle) Tanak, Citrus latipes Hook.f. & Thomson ex Hook.f., Citrus macroptera Montrouz., Citrus micrantha Wester, Citrus papeda Miq., Citrus papuana F.M.Bailey, Citrus southwickii Wester, Citrus torosa Blanco, Citrus tuberoides J.W.Benn., Citrus ventricosa Michel, Citrus vitiensis Yu.Tanak, Citrus westeri Yu.Tanaka, Fortunella sagittifolia K.M.Feng & P.Y.Mao, Papeda rumphii Hassk. 
|Malaysia||Mauritius, limau purut |
|English||Leech-lime  Kaffir lime |
|Indonesia||Jeruk purut, limo purut |
|Thailand||Ma kruut |
|Laos||‘khi ‘hout |
|Philippines||Kabuyau, kulubut (Tagalog); kolobot (Bisaya). |
|Cambodia||krauch soeuch |
|France||Citron combera |
The origin of Citrus hystrix is not known, but it is widely naturalized in Malaysia, Sri Lanka and Burma. 
C. hystrix belongs to the genus Rutaceae. The tree, up to 12 m tall with crooked trunk and short stiff spines. The leaves are broadly ovate to ovate-oblong, 3—15 cm x 2—6 cm. The flowers are small, fragrant and white. The fruits areovoid to ellipsoidal berry, 5—7 cm in diameter, green to yellow, irregularly very bumpy, with 10—12 segments. Often in home gardens, not very vigorous. Hybrid forms exist.
Soil Suitability and Climate Requirement
C. hystrix is very adaptable and can be cultivated on various soil types from the lowland up to about 400 m above sea level with temperature range of 25–38oC. Optimum soil pH is about 6. The plants require 5-6 months of wet season for optimum growth. The area suitable for C. hystrix cultivation must have good drainage with water table at about 50 cm below soil surface during rainy season. The plants perform well in open area with full sunlight.
Area for C. hystrix cultivation should be cleared of all vegetation to prevent disease infections. Planting holes (0.6 m x 0.6 m x 0.6 m) are prepared and 100 g each of organic fertiliser, lime and triple super phosphate are mixed with top soil in the planting holes two weeks before planting. Normal planting distance used is 2.4 m between plants and 3 m between rows giving a population density of 1,380 plants/ha. 
Production of Planting Materials
Grafted seedling using resistant root stocks are normally used as planting materials. Vegetative propagation and seedlings produced from seeds are seldom used as prevention against infections of root rot and virus diseases and root knot nematode infestations. Seedlings obtained from private nurseries should be properly selected to make sure they are healthy and disease-free. Seedlings are ready for planting when they are about 60 cm tall. One to two weeks before field planting, seedlings should be exposed to hardening process to reduce transplanting stress.
Branch and root pruning are conducted before seedlings are planted in the field. Mulch in the form of coconut leaves or rice straws should be provided for each plant after transplanting. However care should be taken to prevent direct contact between mulches and the seedling. Supplemented irrigation is required if transplanting is done during the dry season. Irrigation is required during the dry season for the first two years after transplanting. Plants should be inspected at regular intervals. Dead and unhealthy plants should be uprooted and transplanted with new seedlings.
Urea at the rate of 5 g/plant is applied at monthly intervals until the plants are 1 year old. Organic fertiliser such as chicken manure at the rate of 5 kg/plant is also given twice a year. During the second year, urea is applied twice a year at the rate of 50 g/plant. Application of compound fertiliser (N:P:K=15:15:15) is alternated with urea and applied at the rate of 50 g/plant. Fertiliser rate is increased accordingly until the fifth year when the rate of compound fertiliser used is 700 g/plant and applied twice a year. 
Weeds are controlled by spraying two rounds of contact herbicide and one application of systemic herbicide. Manual weeding using bush cutter is another option for weed management. 
For maintaining optimum crop growth, supplementary irrigation system is needed to provide optimum water supply to the crop during the dry season. Both the sprinkler and rain-gun irrigation system are suitable for C. hystrix. 
Pest and Disease Control
Leaf-miner, Phyllocnistis citrella, is occasionally found attacking the leaves. Infestation is normally low and does not need control measure. Canker, caused by the bacteria, Xanthomonas campestris var citri, can cause serious damage. Canker is controlled by pruning and defoliating heavily infected plants.
Economic harvests of leaves are normally achieved 5 years after planting with an estimated annual yield of 4.5 t fresh leaves/ha. Harvesting is done at 3-4 months intervals. At a recovery rate of 0.8%, the leaves can produce about 36 litres of essential oil (after steam distillation) per year.
Leaves are marketed fresh for culinary purposes. Fresh leaves are also used for essential oil extraction. However, for other uses such as for preparation of traditional medicines and for steam bath, leaves can be air or oven-dried. 
Estimated cost of production
The estimated cost of production for the first year, crop establishment period (year 2 and 3) and fully grown crop (year 4 and above) is RM24, 000, RM5, 700 and RM9, 800 respectively. Based on the fresh yield of about 4.5 t/ha from the fully established crop, the production cost of fresh leaf is about RM2.20 per kg. The production cost was estimated based on the cost of current inputs during writing of this article. 
C. hystrix has been reported to contain sabinene, limonene, β-pinene, citronellal , α-pinene, Terpinen-4-ol, Myrcene, Linalool, α-Thujene , Camphene, δ-2-carene ,γ-terpinene , Terpinolene α-terpineol. 
Plant Part Used
Extract of fruit peel 
C. hystrix leaves are said to have antihistamine, antidandruff, antispasmodic and hypotensive activities. In addition to steam bath, leaves are also used as shampoo especially for dandruff treatment.  The major use seems to be as an insecticide for washing the head and treating the feet to kill land leeches. 
The fruit juice is said can promote gum health and can be used for brushing teeth.  The juice of the fruit is used for seasoning and to prepare drinks. 
Essential oil extracted from the leaves are used as flavouring agents and added in cosmeceutical products such as soaps and lotions. 
Kaffir lime has a very good potential to be explored as sources of natural antioxidants. Studies demonstrated high yield of antioxidants mainly ethanol, flavonoids and phenolic compounds from the extract of kaffir lime leaves. 
In a deep frying experiment, extracts of C. hystrix exhibited protective activity towards refined, leached and deodorised palm olein during frying of fish crackers. The natural antioxidants significantly lowered the rate of oil oxidation during deep-fat frying while maintaining the quality of the crackers. 
Ina preliminary study, C. hystrix oil extract was proven to show high antibacterial properties compared to the fresh extract. It was found to exert inhibitory effects to the growth of Bacillus cereus and Staphylococcus aureus , Listeria monocytogenes, Saccharomyces cereviseae and Aspergillus fumigatus. 
In a separate study, Kaffir lime oil was also found to be inhibitory to Propinibacterium acnes which had a role in the inflammation of acne leading to scar formation. 
Cholinesterase inhibitory activity
Youkwan et al isolated four new compounds, citurosides A-D (1-4) and furanocoumarins with cholinesterase inhibitory activity from the fruit peels of C. hystrix. 
A study conducted in Thailand demonstrated the cytotoxic potential of kaffir lime. Crude extracts from the leaves of kaffir lime (Citrus hystrix DC.) were extracted using hexane, ethanol, ethyl acetate, butanol and methanol. The fractions were investigated in vitro for their potential cytotoxic activity on HL60, K562, Molt4, U937 cell lines, and normal human peripheral blood mononuclear cells (PBMCs) using the MTT assay. The in vitro cytotoxicity bioassays on 4 leukemic cell lines showed that the ethyl acetate fraction exhibited the highest cytotoxicity, giving it a positive outlook in its possible use in chemotherapy. 
Cardioprotective, hepatoprotective activity
A study was conducted to observe the combination effect of doxorubicin and C. hystrix (kaffir lime’s) peel ethanolic extract (ChEE) on blood serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) activity and cardio-hepato-histopathology of female Sprague Dawley rats. This experiment demonstrated that ChEE repaired cardiohistopathology profile of doxorubicin induced cardiotoxicity and hepatotoxicity in the rats, but did not repair neither hepatohistopathology profile nor reduce serum activity of ALT and AST. 
Autonomic stimulating activity
The effects of kaffir lime oil on human autonomic and behavioural parameters after massage were investigated in a study conducted on forty healthy volunteer. Autonomic parameters recorded were skin temperature, pulse rate, breathing rate and blood pressure. Behavioural parameters were assessed by means of visual analogue scales (VAS). The kaffir lime oil caused a significant increase in blood pressure and a significant decrease in skin temperature. Regarding the behavioural parameters, subjects in the kaffir lime oil group rated themselves more alert, attentive, cheerful and vigorous than subjects in the control group. These findings are likely to represent stimulating/activating effects of the kaffir lime oil and provide some evidence for the use of kaffir lime oil in aromatherapy, such as causing relief from depression and stress in humans. 
- The Plant List. Ver 1.1. Citrus hystrix DC. [homepage on the Internet]. c2013 [updated 2012 Mar 23; cited 2016 July 18]. Available from: http://www.theplantlist.org/tpl1.1/record/kew-2724129
- Jansen PCM, Jukema J, Oyen LPA, van Lingen TG. Citrus hystrix DC. In: Verheij EWM, Coronel RE, editors. Plant Resources of South-East Asia No. 2: Edible fruits and nuts. Wageningen, Netherlands: Pudoc, 1991; p. 326.
- Kasuan N, Muhammad Z, et al. Extraction of Citrus Hystrix DC (Kaffir Lime) essential oil using automated steam distillation process: Analysis of volatile compounds. Malays J Anal Sci. 2013;17(3):359-369.
- Yahaya H, Ahmad Puat N. Limau purut (Citrus hystrix). In: Musa Y, Muhammad Ghawas M, et al. Penanaman tumbuhan ubatan & beraroma. Serdang: MARDI, 2005; p. 108-117.
- Anon. Compendium of medicinal plants used in Malaysia. Volume 1. Kuala Lumpur: Institute of Medical Research, 2002; p. 194.
- Mat-Salleh K, Latiff A, editor. Tumbuhan ubatan Malaysia. Bangi, Selangor: Pusat Pengurusan Penyelidikan Universiti Kebangsaan Malaysia, 2002; p. 470.
- Verheij EWM, Coronel RE, editors. Project Plant Resources of South-East Asia No.2: Edible fruits and nuts. Wageningen: Pudoc, 1991; p.119-120
- Butryee C, Sungpuag P, Chitchumroonchokchai C. Effect of processing on the flavonoid content and antioxidant capacity of Citrus hystrix leaf. Int J Food Sci Nutr. 2009;60 Suppl 2:162-174.
- Jamilah B, Man YB, Ching TL. Antioxidant activity of Citrus hystrix peel extract in RBD palm olein during frying of fish crackers. J Food Lipids. 1998;5(2):149-157.
- Chaisawadi S, Thongbute D, Methawiriyasilp W, et al. Preliminary study of antimicrobial activities on medicinal herbs of Thai food ingredients. Acta Hortic. 2005;675:111-114.
- Chanthaphon S, Chanthachum S, Hongpattarakere T. Antimicrobial activities of essential oils and crude extracts from tropical Citrus spp. against food-related microorganisms. Sonklanakarin. J Sci Tech. 2008;30(1):125.
- Lertsatitthanakorn P, Taweechaisupapong S, Aromdeea C, Khunkittia W. In vitro bioactivities of essential oils used for acne control. Int J Aroma. 2006;16(1):43–49.
- Youkwan J, Sutthivaiyakit S, Sutthivaiyakit P. Citrusosides A− D and furanocoumarins with cholinesterase inhibitory activity from the fruit peels of Citrus hystrix. J Nat Prod. 2010;73(11):1879-1883.
- Chueahongthong F, Ampasavate C, Okonogi S, Anuchapreeda S. Cytotoxic effects of crude kaffir lime (Citrus hystrix, DC.) leaf fractional extracts on leukemic cell lines. J Med Plants Res. 2011 Jul 18;5(14):3097-105.
- Putri H, Nagadi S, Larasati YA, et al. Cardioprotective and hepatoprotective effects of Citrus hystrix peels extract on rats model. Asian Pac J Trop Biomed. 2013;3(5):371-375.
- Hongratanaworakit T, Buchbauer G. Chemical composition and stimulating effect of Citrus hystrix oil on humans. Flavour Frag J. 2007;22(5):443-449.