natto, known as nattō-kin in Japanese. Other ingredients may be added by some manufacturers. From this point on, care has to be taken to keep the ingredients away from impurities and other bacteria. The mixture is fermented at 40°C for up to 24 hours. Afterwards the natto is cooled, then aged in a refrigerator for up to one week to add stringiness. During the aging process at a temperature of about 0°C, the Bacilli develop spores, and enzymatic peptidases break down the soybean protein into its constituent amino acids.
Historically, natto was made by storing the steamed soy beans in rice straw, which naturally contains B. natto. The natto was packed in straw and then left to ferment by itself. The fermentation was done either while the beans were buried underground underneath a fire or stored in a warm place in the house as for example under the kotatsu.
End product
Today's nattoToday's mass-produced natto is usually sold in small polystyrene containers. A typical package contains 2 or 3 containers, occasionally 4 containers, each of 40 to 50 g. One container typically complements a small bowl of rice. It usually includes a small packet of tsuyu and another packet of yellow mustard. Other flavors of sauce, such as shiso, are available.
Mito City and Kumamoto Prefecture are famous as natto-producing districts. Outside of Japan, natto is sometimes sold frozen, and must be thawed before consumption.
History
The materials and tools needed to produce natto (soybeans and straw) were commonly available in Japan since ancient times, so the discovery could have happened as early as in the Jomon period. It may also be possible that the product was discovered independently by numerous people at different times. The sources differ about the earliest origin of natto. One source puts the first use of natto in the Jomon period between 10,000 BC to 300 BC. According to other sources the product may also have originated in China during the Zhou Dynasty (1134 BC - 246 BC). Another story is that Yoshiie Minamoto was on a battle campaign in northeastern Japan between 1056 and 1063 and another campaign between 1086 and 1088 when one day in 1083 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, at which time the beans had fermented. The soldiers ate it anyway, and liked the taste, so they offered some to their commander Yoshiie Minamoto who also liked the taste. A third source calls the origin of natto fairly recent from the Edo period (1603 to 1867).
One significant change in the production of natto happened in the Taisho period (1912 - 1926), when researchers discovered a way to produce the natto yeast containing the Bacillus natto without the need for straw. This greatly simplified the production process and enabled more consistent results.
Medical benefits
Natto is claimed to have many medical benefits, and Japanese often say that eating natto is good for your health. Some of these claims are backed by medical research. Natto for example contains a compound Pyrazine, which not only gives natto its distinct smell, but also reduces the likelihood of blood clotting. It also contains a serine protease type enzyme called nattokinase which may also 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 natto containing nattokinase is available as a dietary supplement. Studies have shown that oral administration of nattokinase 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.
Natto also contains large amounts of Vitamin K, 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 seaweed, liver and some vegetables, while vitamin K2 is found in fermented food products like cheese and miso. Natto has very large amounts of vitamin K2, approximately 870 micrograms per 100 grams of natto.
Natto also contains many chemicals alleged to prevent cancer, as for example daidzein, genistein, infrabin, phytoestrogen, and the chemical element selenium. However, most of these chemicals can also be found in other soy bean products, and their effect on cancer prevention is uncertain at best. Some sources also claim that natto has a cholesterol-lowering effect.
Natto is also said to have an antibiotic effect, and was used as medicine against dysentery by the Imperial Japanese Army before World War II. Furthermore, natto is said to improve digestion, reduce the effects of aging, and to prevent obesity (also possibly due to a low calorie content of approximately 90 calories per 7-8 grams of protein in an average serving), although this seems to be based only on an analysis of the chemicals contained in natto, and not on any medical study.
Natto is also sometimes used as an ingredient of pet food, and it is claimed that this improves the health of the pets.
Natto is known to reverse hair loss in men due to phytoestrogens, which can lower testosterone that causes baldness. |
