Natto is possibly one of the smelliest foodstuffs around but it might just be the next superfood. It is a traditional dish with a strong flavour and slimy texture. The food was originally from northern parts of Japan where it has been part of their cuisine culture for absolutely ages. It was written about at least 1,000 years ago. The legend is that a military officer in the East-Northern District of Japan developed it as a military ration.
Essentially, natto is fermented soybean which is similar to tempeh. We already know that soybeans are healthy nutritious legumes in their own right with many benefits. I’m sure many of us have eaten edamame beans for example.
There are three types of natto: itohiki‐natto, yukiwai‐natto, and hama‐natto (daitokuji temple natto). Itohiki‐natto is nowadays the most popular and produced in large amounts. The word “natto” often refers to itohiki‐natto although it is possible to find the other forms (Fukushima, 1986). The itohiki form is an unsalted version whilst the hama version is salted.
One version known as cracked natto uses parched soybeans which are cracked.
We tend to think of yeast fermentation as the predominant method for fermenting foods but this is one that relies on a single bacterium known as Bacillus natto. This bacteria is related to Bacillus subtilis which is a common industrial bacteria for producing a range of proteases and other commercially important materials. The bacteria B. natto is an aerobic Gram‐positive rod.
Natto probably does not win awards for appearance. It has a particularly characteristic aroma and rather musty flavour. To some it reminds them of a highly pungent cheese and one in particular springs to mind which is Bishops Finger. The aroma is enough to put others off but for some it is an absolute delicacy. The flavour however is more nutty. It is also slimy because it is covered with sticky viscous polymers of glutamic acid. This slimy material is produced by the bacteria and confers the esteemed health properties. If you find it in Japanese supermarkets, it is usually sold covered with a white mucous like membrane. It should have the characteristic odour, be soft in texture but not gagging and a light yellow, almost beige colour. Chopsticks are the traditional implements to get this soybean to the mouth and it is often turned into a sticky, silky but glutinous mass when stirred in the bowl with these chopsticks. Serve with rice for a digestive especially at breakfast.
Fermentation Of Natto
Natto is relatively cheap to produce and the process of fermentation is not that complex either. Most households used to produce their own.
The basic method is to presoak the soybeans so as to soften them up. These are cooked until tender, drained and cooled to around 40 °C. The bacteria is added as a suspension and thoroughly mixed in. Natto used to be packed into wooden boxes for fermentation but polyethylene bags are preferred for convenience. These are incubated for between 40 and 45 Centigrade for 12 to 20 hours (Snyder & Kwon, 1987).
Different fermentation times produce different qualities depending on how much change is desired. The key is not just the nutritional quality but the final taste and texture. If the fermentation is only 6 hours, the natto has a taste similar to the soybean but without too much of the ‘cheesy’ smell. It is only in recent years that fermentation times have got longer to make the product more interesting in flavour.
Extremely complex biochemical reactions occur in natto production. The quality depends on the degree and relative rates of reaction taking place. These are all affected by soaking, salt content, steaming levels, type of fermentation and what bacteria strains are used (Wei et al., 2001).
The fermentation also produces an enzyme called nattokinase which has reported health benefits as a supplement.
Nutrition Of Natto
It contains a variety of nutrients, most of which are derived from the soybean itself. The compounds produced by the bacteria are important for optimal health. The high fiber content means that it is a good food for speeding up transit times through the gut. That implies it adds bulk to stools and promotes regular bowel movements and alleviates constipation.
The food is also high in vitamin K (menaquinone-7) which we know has benefits in calcium metabolism, bone growth and immunity. In Japan, a couple of studies showed that a regular natto intake was associated with reduced bone loss especially in those who were postmenopausal (Ikeda et al., 2006). The food conatins roughly 100 times for menaquinone-7 than certain types of cheese (Katsuyama et al., 2002).
The food composition is about 59.5% moisture, 16.5% protein, and 10.0% lipid (Ohta, 1986).
A 3.5-ounce (100-gram) portion provides the following:
- Calories: 212
- Fat: 11 grams
- Carbs: 14 grams
- Fiber: 5 – 5.4 grams
- Protein: 18 grams
- Manganese: 76% of the RDI
- Iron: 48% of the RDI
- Copper: 33% of the RDI
- Vitamin K1: 29% of the RDI
- Magnesium: 29% of the RDI
- Calcium: 22% of the RDI
- Vitamin C: 22% of the RDI
- Potassium: 21% of the RDI
- Zinc: 20% of the RDI
- Selenium: 13% of the RDI
The process of manufacture is through fermentation. This has been refined over many years and a number of innovations made to ensure the best quality and consistent natto is produced.
Nattokinase is an enzyme produced during fermentation which is used as a supplement. A small study with 12 young Japanese men showed that a single supplementation helped prevent and dissolve blood clots although further research is needed to corroborate such a finding (Kurosawa et al., 2015).
The enzyme is also associated with reducing blood pressure – diastolic and systolic. One study; an 8 week one in Japan showed that both diastolic and systolic blood pressure dropped by 2.84 and 5.55 mmHg, respectively (Kim et al., 2008). A later study reported in 2016 found similar benefits in a better controlled randomized, double-blind and placebo-controlled study in North America (Jensen et al. 2016). This 8 week study also showed a a drop of 3 and 4 mmHg respectively. This more extensive study revealed a potential enzyme addition for dissolving and breaking up blood clots.
References
. 1986. Soy sauce and other fermented foods of Japan. In: Mycologia Memoir. St. Paul : APS Press. pp. 121–49.
Ikeda, Y., Iki, M., Morita, A., Kajita, E., Kagamimori, S., Kagawa, Y., & Yoneshima, H. (2006). Intake of fermented soybeans, natto, is associated with reduced bone loss in postmenopausal women: Japanese Population-Based Osteoporosis (JPOS) Study. The journal of nutrition, 136(5), 1323-1328. https://doi.org/10.1093/jn/136.5.1323
Jensen GS, Lenninger M, Ero MP, Benson KF. (2016) Consumption of nattokinase is associated with reduced blood pressure and von Willebrand factor, a cardiovascular risk marker: results from a randomized, double-blind, placebo-controlled, multicenter North American clinical trial. Integr. Blood Press Control. Oct 13;9 pp. 95-104. doi: 10.2147/IBPC.S99553. PMID: 27785095; PMCID: PMC5066864 (Article).
Katsuyama, H., Ideguchi, S., Fukunaga, M., Saijoh, K., & Sunami, S. (2002). Usual dietary intake of fermented soybeans (Natto) is associated with bone mineral density in premenopausal women. Journal of Nutritional Science and Vitaminology, 48(3), pp. 207-215
Kim JY, Gum SN, Paik JK, Lim HH, Kim KC, Ogasawara K, Inoue K, Park S, Jang Y, Lee JH. (2008) Effects of nattokinase on blood pressure: a randomized, controlled trial. Hypertens Res. 2008 Aug;31(8):1583-8. doi: 10.1291/hypres.31.1583. PMID: 18971533.
Kurosawa, Y., Nirengi, S., Homma T, Esaki K, Ohta M, Clark JF, Hamaoka T. (2015) A single-dose of oral nattokinase potentiates thrombolysis and anti-coagulation profiles. Sci. Rep. Jun 25;5:11601. doi: 10.1038/srep11601. PMID: 26109079; PMCID: PMC4479826.
Ohta, T. (1986) Natto. Ch. 5 in Legume-based Fermented Foods NR Reddy, MD Pier- son. D Merle, DK Salunkhe, Ed. Boca Raton, FLA: CRC Press. p 85-93
, . 1987. Soybean utilization. New York : Van Nostrand Reinhold. 346 p. (Article)
, , . 2001. Natto characteristics as affected by steaming time, Bacillus strain, and fermentation time. J Food Sci 66:167–73 (Article
Yanagisawa Y, Chatake T, Chiba-Kamoshida K, et al. (2010) Purification, crystallization and preliminary X-ray diffraction experiment of nattokinase from Bacillus subtilis natto. Acta Crystallogr Sect F Struct Biol Cryst Commun. 66(12): pp. 1670–1673.
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