Sudachi (Citrus sudachi Hort. ex Shirai) is a small, round, green citrus fruit of Japanese origin. Tokushima Prefecture produces 98% of the sudachi grown in Japan. The fruit weighs 20-25 g, and up to 40 g. It is normally harvested and used while still green, although it eventually develops a yellow-orange rind. The plant has white flowers which bloom in May and June. The fruits form in bunches and are harvested in the fall. The fruit contains large smooth seeds with a green polyembryo.
Genetic analysis shows sudachi to be the product of a cross between a yuzu and another citrus fruit akin to the koji and tachibana orange. Most modern scientists do not consider it a bona fide species, but a cultivar or a hybrid of uncertain parentage.
Classification and Cultivation
In the Swingle scheme the sudachi was classed within the Papeda subgenus, and in the more complicated scheme of Tyozaburo Tanaka it falls within the Eusmocitrus or true yuzu subgenus, under the Osmocitrus or yuzu section. Both sudachi and kabosu are descendants of yuzu and relatives of the Unshū mikan, yet each has markedly different aromas, flavors and textures.
Despite its small size the fruit holds plenty of seeds. The top producing communities are the township of Kamiyama-cho and the village of Sanagouchi-son, which together accounted for almost half of the prefecture's annual production in 2008. Tokushima is also one of the prefectures with the largest citrus-growing areas of Japan, together with Wakayama, Shizuoka, Kochi, Oita, Miyazaki and Ehime.
Production and Geographical Indication
The fruit is harvested when the skin is dark green, and consumers value it for its refreshing aroma and acidity. Commercial cultivation began around 1965; Tokushima then developed and selected superior varieties, and the fruit has since spread across the country.
Chemistry
Sudachitin, a polymethoxyflavone, is found in the peel of Citrus sudachi. 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. Neoeriocitrin, a flavonoid characteristic of the daidai, is also found in sudachi juice and rind. Sudachi juice contains about 3 times as much narirutin as yuzu juice, at 20.1 mg per 100 ml against 6.6 mg.
The peels of sour citruses such as sudachi contain essential oils like limonene and a variety of other aromatic components. Enantioselective gas chromatography of sudachi peel oils showed highly significant differences between the two isomers of linalool and α-pinene in both odor detection thresholds and odor qualities. By limited odor units, linalool, octanal, limonene, α-pinene, p-cymene, γ-terpinene, myrcene, 1,8-cineole, citronellal, decanal, α-phellandrene and dodecanal contribute to the aroma of Citrus sudachi.
Eriocitrin is an antioxidant reported to combat lipid peroxidation. Narirutin is quite abundant in the rind of yuzu and kabosu. Sudachitin is 5,7,4'-trihydroxy-6,8,3'-trimethoxyflavone and is structurally similar to nobiletin. The ability of the sudachi to promote the body's calcium absorption has been studied. The refreshing flavor of sour citruses such as sudachi comes from high levels of citric and malic acids and amino acids, and the fruits are full of vitamin C.
Among the odor-contributing compounds of the peel oil are both enantiomers of linalool, (3S)-(+) and (3R)-(−), as well as (4R)-(+)-limonene, (1R,5R)-(+)-α-pinene and (3R)-(+)-citronellal. Cumin aldehyde, dill ether, diisopropyl disulfide, (E,E)-α-farnesene and (E)-β-farnesene were newly selected as aroma-active compounds of sudachi essential oil.
Culinary Use
Sudachi is sour and is not consumed whole, but normally squeezed like a lemon or lime to flavor food. A half-slice of the fruit is served as garnish with many traditional Japanese dishes, including fish, soba, udon and nabe. In Tokushima, sudachi vinegar is the standard choice for sushi, and in Osaka bold sudachi ponzu is preferred. Sudachi has a higher calcium and ascorbic acid content than lemons. Sudachi-flavored products such as ice cream, vodka coolers, ice pops and soft drinks can be found in Japan.
Japan has over 40 varieties of highly acidic sour citrus used primarily for flavoring, and sudachi is one of them. The flesh of such fruits is too acidic to be eaten as it is; the aromatic peels and sour juices accentuate other foods, much as lemons or limes do in the West. The juice of these fruits has long been used in place of vinegar, and in landlocked areas where fresh fish was unavailable it served as a preservative against food poisoning from perishable animal meats. Harvested before it ripens fully, the tart sudachi flavors sauces and marinades, desserts and drinks in place of lemon or lime, and its juice serves as an acidulant instead of brewed vinegar. Ponzu, a citrus-based Japanese sauce, often includes sudachi along with other bitter oranges.
The fruit is also a match for alcoholic drinks such as shōchū with soda, and it is used to add aroma to noodles like soba, sōmen and udon. In Tokushima the fruit is sold cheaply, while in other parts of Japan it is considered a delicacy and is often expensive.
