Nattō (なっとう or 納豆?) is a traditional Japanese food made from soybeans fermented with Bacillus subtilis. Some eat it as a breakfast food. Nattō may be an acquired taste because of its powerful smell, strong flavor, and slimy texture. In Japan nattō is most popular in the eastern regions, including Kantō, Tōhoku, and Hokkaido.
Sources differ about the earliest origin of nattō. The materials and tools needed to produce nattō commonly have been available in Japan since ancient times. There is also the story about Minamoto no Yoshiie who was on a battle campaign in northeastern Japan between 1086 AD and 1088 AD when one day they were attacked while boiling soybeans for their horses. They hurriedly packed up the beans, and did not open the straw bags until a few days later, by which time the beans had fermented. The soldiers ate it anyway, and liked the taste, so they offered some to Yoshiie, who also liked the taste. It is even possible that the product was discovered independently at different times.
One significant change in the production of nattō happened in the Taishō period (1912–1926), when researchers discovered a way to produce a nattō starter culture containing Bacillus subtilis without the need for straw. This simplified production and permitted more consistent results.
Appearance and consumption
||This section possibly contains original research. (December 2012)|
Nattō is occasionally used in other foods, such as nattō sushi, nattō toast, in miso soup, tamagoyaki, salad, as an ingredient in okonomiyaki, or even with spaghetti. Sometimes soybeans are crushed and fermented. This is called 'hikiwari nattō'.
Many non-Japanese find the taste unpleasant and smelly, while others relish it as a delicacy.
Nattō is more popular in some areas of Japan than in others. Nattō is known to be popular in the eastern Kantō region, but less popular in Kansai. A 2009 internet survey in Japan indicated 70.2% of respondents like Natto and 29.8% do not, but out of 29.8% who dislike Natto, about half of them eat natto for its health benefits.
Nattō is made from soybeans, typically nattō soybeans. Smaller beans are preferred, as the fermentation process will be able to reach the center of the bean more easily. The beans are washed and soaked in water for 12 to 20 hours to increase their size. Next, the soybeans are steamed for 6 hours, although a pressure cooker may be used to reduce the time. The beans are mixed with the bacterium Bacillus subtilis, known as nattō-kin in Japanese. From this point on, care must to be taken to keep the ingredients away from impurities and other bacteria. The mixture is fermented at 40 °C (104 °F) for up to 24 hours. Afterward the nattō is cooled, then aged in a refrigerator for up to one week to allow the development of stringiness.
In Natto making facilities, these processing steps have to be done by avoiding incidents in which soybeans are touched by workers. Even though workers use B. subtilis natto as the starting culture which can suppress some of other undesired bacterial growth, workers pay an extra-close attention not to introduce skin flora onto soy beans. 
To make nattō at home, a bacterial culture of B. subtilis is needed. B. subtilis natto is weak in lactic acid, so it is important to prevent lactic acid bacteria from breeding. Some B. subtilis natto varieties that are more odorless are usually less active, raising the possibility that minor germs will breed. Bacteriophages are dangerous to B. subtilis.
Historically, nattō was made by storing the steamed soybeans in rice straw, which naturally contains B. subtilis natto. The soybeans were packed in straw and left to ferment.
Today's mass-produced nattō is sold in small polystyrene containers. A typical package contains two, three, or occasionally four containers, each 40 to 50 g. One container typically complements a small bowl of rice.
Natto has a different nutritional makeup from raw soy beans, losing Vitamin A and several other vitamins and minerals. However, the calorie content of natto is lower than that of raw soy beans. While soy beans are highly nutritious, the nutrition is packed in the bean's hard fiber. Natto includes the benefits of nutritious soy and softer dietary fiber without the high sodium content present in many other soy products, notably in miso. Natto contains no cholesterol and is a significant source of iron, calcium, magnesium, protein, potassium, vitamins B6, B2, E, K2 and more.   When Natto is mixed with egg and eaten with rice, Japanese call the dish a perfectly nutritious meal, covering all nutritional needs.
When Bacillus subtilis natto breaks up soy protein, the bacteria creates chains of polyglutamic acid, Gamma polyglutamic acid. This polypeptide chain is unusual in that the peptide bond is found between the nitrogen and the R-group’s carboxyl acid.
The Japanese media frequently claim, especially in television shows for health-concerned viewers, that nattō is health-enhancing and that these claims are backed by medical research.[original research?]
Medicinal isolates of nattō include pyrazine and tetramethylpyrazine. Pyrazine is a compound that, in addition to giving nattō its distinct smell, reduces the likelihood of blood clotting. It also contains a serine protease type enzyme called nattokinase which also may reduce blood clotting both by direct fibrinolysis of clots, and inhibition of the plasma protein plasminogen activator inhibitor 1. This may help to avoid thrombosis, as for example in heart attacks, pulmonary embolism, or strokes.
An extract from nattō containing nattokinase is available as a dietary supplement. Studies have shown that oral administration of nattokinase in enteric capsules leads to a mild enhancement of fibrinolytic activity in rats and dogs. It is, therefore, plausible to hypothesize that nattokinase might reduce blood clots in humans—although clinical trials have not been conducted. Another study suggests that Fibrinolysis Accelerating Substance (FAS) in natto is the substance which initiates fibrinolysis of clots, which accelerates the activity of not only nattokinase, but urokinase.
A 2009 study in Taiwan indicated that the nattokinase in natto has the ability to degrade amyloid fibrils, suggesting that it might be a preventative or a treatment for amyloid-type diseases such as Alzheimer's.
Natto is rich in vitamin K. It contains large amounts of vitamin K2, which is involved in the formation of calcium-binding groups in proteins, assisting the formation of bone and preventing osteoporosis. Vitamin K1 is found naturally in leafy greens, seaweed, liver, and some vegetables, while vitamin K2 (Menatetrenone) is found in fermented food products such as cheese, miso, and Nattō.
According to recent studies, polyamine suppresses excessive immune reactions, and nattō has a much larger amount of it than any other food. Dietary supplements containing the substances extracted from natto such as polyamine, nattokinase, FAS, and vitamin K2 are available.
Nattō contains chemicals alleged to prevent cancer, for example, daidzein, genistein, isoflavone, phytoestrogen, and the chemical element selenium, however, most of these chemicals also may be found in other soybean products, and their effect on cancer prevention is uncertain.
Natto’s polyglutamic acid is useful as an organic polymer coagulant. Polyglutamic acid is useful in making organic and inexpensive water cleaner products, PGα21Ca, sold as a powder.
Close relatives of natto
Many countries produce similar traditional soybean foods fermented with Bacillus subtilis, such as shuǐdòuchǐ (水豆豉) of China, cheonggukjang (청국장) of Korea, thuanao (ถั่วเน่า) of Thailand, kinema of Nepal and the Himalayan regions of West Bengal and Sikkim, hawaijaar of Manipur, akhuni of Nagaland, piak of Arunachal Pradesh, India. 
Nattō gunkan maki (Nattō sushi)
- Amanattō – is not nattō, but rather, beans sweetened with sugar
- Fermented bean paste
- Japanese cuisine – Other fermented soy foods include soy sauce, Japanese miso, Chinese dòuchǐ (fermented black soybeans), fermented tofu and (a subcategory) chòu dòufu (stinky tofu), Korean doenjang, Meju, and cheonggukjang, Nepalese kinema, and Indonesian tempeh and oncom.
- List of fermented soy products
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