Sudachi (Citrus sudachi; Japanese: スダチ or 酢橘) is a small, round, green, Japanese citrus fruit that is a specialty of Tokushima Prefecture in Japan. It is a sour citrus, not eaten as fruit, but used as food flavoring in place of vinegar.
Cultivated for centuries in parts of Japan, and perhaps nearly as well known as another sour citrus, the yuzu in that country, it has been considered an "indispensable companion" to eating matsutake mushroom. The ponzu (ポン酢?, "pon vinegar"), the squeezed citrus juice used as an alternative to vinegar uses sudachi among other bitter oranges (kabosu or yuzu juices, and daidai) as an ingredient.
The fruit is also the symbol of the prefecture of Tokushima where the majority of the fruit is cultivated. Cultivation is centered mainly in the communities of Sanagouchi-son, Kamikatsu-cho and Kamiyama-cho. The plant has white flowers which bloom in May and June. The fruits form in bunches, or tight clusters, and are harvested in the fall. Though sudachi fruits will eventually develop a yellow-orange rind color, they are normally harvested and used while still green. They contain large smooth seeds, containing a green polyembryo.
A half-slice of this fruit is served as garnish with many traditional Japanese dishes which include fish, soba, udon, nabe, and even some alcoholic beverages. It is considered to have a zestier flavor and aroma than lemons or limes. It also boasts a higher calcium and ascorbic acid (vitamin C) content than lemons. Sudachi flavored products (such as ice cream, vodka coolers, ice pops, and soft drinks) can also be found in Japan, particularly in Tokushima Prefecture, where the fruit is sold cheaply. The actual fruit is regarded as a delicacy in other parts of Japan, and is often expensive. Compared to the related kabosu, sudachi is much smaller at 20-25 to 40 grams as compared to 100 to 140 grams.
Its species name was published by Mitsutaro Shirai (1933), but most modern scientists, even while still using this nomenclature by habit or as legacy, do not consider it as a bona fide species, but regard it as a cultivar  of unknown parentage, or a cultigen of the yuzu
The sudachi is classed within the Papeda subgenus in the Swingle scheme, and in the more complicated Tanaka scheme within the Eusmocitrus or true yuzu subgenus, under the Osmocitrus or yuzu section.
The flavonoid eriocitrin abundant in lemon and lime juices is present in comparable concentrations in sudachi juice, but is lacking in yuzu or kabosu juices. Also, neoeriocitrin (characteristic in bergamot daidai) is found in sudachi juice and rind  Eriocitrin is an antioxidant reported to combat lipid peroxidation and like neoeriocitrin is said to block the formation of lipoxygenases involved in allergies and atherosclerosis.。
Also, the flavonoid narirutin is said to be the active chemical in the Wakayama Prefecture specialty citrus jabara juice (ja:ジャバラ) that is said to diminish the effects of pollen allergies. The jabara advertises that it contains 6 times the narirutin in yuzu, but sudachi juice also contains about 3 times as much as yuzu juice (20.1 mg per 100 ml, vs. 6.6 mg). But it should be noted this substance is quite abundant in the rind of yuzu and kabosu.
The ability of the sudachi to promote the body's calcium absorption has been studied as well.。
In 2006, a Tokushima University research team published a report which suggests that the fruit may be effective in lowering glucose levels in diabetic patients. The team gave rats sudachi zest over a one year period and found the glucose levels fell and the health of the rats to improve.）
- A discourse on Japanese names of trees (Jumoku Wamei Ko) 114, index 8. 1933, "Citrus sudachi hort. ex Shirai". Germplasm Resources Information Network (GRIN) online database.
- Schmadel 2012, p. 815
- Iuchi, Akira; Hayashi, Katsuo; Tamura, Katsuhiro; Kono, Toshitaka (1996). "Technique of quality control for Sudachi (Citrus sudachi Hort. ex Shirai) juice by high pressure treatment". In Balny, R.; Hayashi. Dictionary of Minor Planet Names (sixth edition). High Pressure Bioscience and Biotechnology. Mitsuo MIyashita, Swapan K. Chakraborty (Elsevier). p. 387. ISBN 9780080544618.
Sudachi (Citrus sudachi Hort. ex Shirai) is a cultivated variety of sour orange which is grown in Tokushima Prefecture, Japan. The juice of this fruit is widely used as an acidulantinstead of brewed vinegar..
- Tanaka & Taninaka 1960, p. 10
- Okuyama, Masuaki (奧山益朗) (2001). Mikaku hyōgen jiten (味覚表現辞典) (SNIPPET). 松茸には欠かせないスダチの風味: 東京堂出版. p. 224.
- Wardowski, Wilfred F.; Nagy, Steven; Grierson, William (1986). Fresh citrus fruits - 150 (SNIPPET). AVI Pub. Co.,. p. 150. ISBN 9780870555190.
Sudachi bears small fruit (20-25 g) and is traditionally grown in Tokushima Prefecture. The fruit are harvested only at the green stage and are served in cut halves as a garnish
- Tanaka & Taninaka 1960, p. 12
- Tanaka & Taninaka 1960, pp. 9–10
- Miyake, Yoshiaki (2006). "Characteristics of Flavonoids in Niihime Fruit - a New Sour Citrus Fruit" (PDF). Food Science and Technology Research (Food Sci. Technol.) 12 (3): 186–193. doi:10.3136/fstr.12.186. JOI:JST.JSTAGE/fstr/12.186.
- Kawaii, S. (1999b). Tomono, Y., Katase, E., Ogawa, K. and Yano, M.. "Quantitation of flavonoid constituents in citrus fruits. J.". Journal of Agricultural and Food Chemistry 47: 3565–3571. doi:10.1021/jf990153+. also reports eriocitrin in sudachi.
- (Miyake 2006, p. 186)
- Japan's NARO (National Agriculture and Food Research Organization) site：近畿中国四国農業研究センター (2005). "エリオジクチオール及びその配糖体のアラキドン酸代謝系リポキシゲナーゼ阻害効果".
- 野方, 洋一 (Nogata, Yoh-ichi) (2002-09-30). "機能性成分を高濃度に含有するポンカン果汁の製造法 (特集 果実・果汁の機能性成分とその利用(2)". The Food industry 45 (18): 27–34. ISSN 0559-8990. NAID 40005445401., etc.
- Nii, Yoshitaka (新居佳孝). Fukuta, K., Sakai, K. and Yamamoto, S.. "Japanese citrus fruit (sudachi) juice is associated with increased bioavailability of calcium from whole small fish and suppressed bone resorption in rats (スダチ果汁添加による小魚カルシウムの吸収促進および骨吸収抑制効果)". Journal of nutritional science and vitaminology (J. Nutr. Sci. Vitaminol. 50 (3): 177–183. ISSN 0301-4800. doi:10.3177/jnsv.50.177.
- 田中直伸; 中川博之 (October 2006). 橋田 和佳, 佐藤 昌俊, 奥瀬 由惟, 田岡 千明, 岩永 智史, 土屋 浩一郎, 高石 喜久. "スダチ (Citrus sudachi)の含有成分並びに血糖値上昇抑制作用について (Sudachi (Citrus sudachi) no ganyū seibun narabi ni kettōchi jōshō yokusei sayō ni tsuite)". 第一回食品薬学シンポジウム (1st food-product pharmaceutics symposium).. This is no a CiNii databased paper.[dead link]
- "スダチの搾りかすに血糖値抑制効果、徳島大教授ら発表 : ニュース : 医療と介護 (Sudachi no shibori kasu ni kettōchi yokusei kōka, Tokushimadai kyōju ra happyō)". 読売新聞（YOMIURI ONLINE）. 2006-08-30.[dead link]
- Tanaka, Tyozaburo; Taninaka, Tokio (1960-03-31). "A Revision of Osmocitrus, a section of the genus Citrus : Revisio Aurantiacearum XIII" (PDF). Bulletin of the University of Osaka Prefecture. Ser. B, Agriculture and biology (64): 9–13. pdf
- Schmadel, Lutz D. (2012). Dictionary of Minor Planet Names (sixth edition). Springer. p. 815. ISBN 9783642297182.
- Sudachi at Citrus Variety Collection website
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