Jump to content

Course:FNH200/Projects/2025/Natto

From UBC Wiki

Introduction

Natto is a traditional Japanese fermented soybean product known for its pungent smell, slimy texture, and distinctive taste.[1] The exact origin of natto is unclear; however, it is believed to have been accidentally discovered by Hachimantaro Yoshiie.[2] Legend has it that he wrapped steamed soybeans in rice straw and stored them on his horse, where the warmth created the ideal environment for fermentation to occur.[2] Today, natto is commonly eaten for breakfast in Japan, often served atop a bowl of rice or miso soup with condiments such as mustard, soy sauce, and/or green onion.[3]

Natto topped with green onion[4]

Studies have shown that natto is rich in protein, fiber, vitamin K2, and some minerals.[1][5] These nutrients are associated with many health benefits, including improved cardiovascular health, enhanced immune function, fat reduction, and promotion of bone growth.[5][6] Due to its high nutritional value, natto has gained increasing popularity worldwide. However, there is also evidence suggesting that natto may pose risks for certain individuals, particularly those taking blood-thinning medications due to nattokinase, an enzyme in natto that has anticoagulation properties.[6]

Fermentation

Natto is produced through the bacterial fermentation of green or black soybeans using Bacillus subtilis.[7] Unlike many other fermented foods that rely on mixed microbial communities, natto fermentation is dominated by this single bacterial species.[8] B. subtilis is an aerobic, gram-positive bacterium capable of forming endospores under harsh environmental conditions. Its optimal growth temperature ranges from 30 to 35°C.[9][10] The strain used in most natto production is B. subtilis natto.[11] In the fermentation process, the bacterium secretes enzymes that break down soybean proteins into peptides and amino acids.[7] Poly-γ-glutamic acids are also produced by the bacterium during this time, ultimately resulting in the formation of sticky long threads that give natto its unique texture.[11] Secondary fermentation should be avoided, as it will result in the production of ammonia and promote spoilage-causing organisms.[11] Natto can also be produced through fermentation by mould cultures, such as Aspergillus oryzae, Rhizopus oligosporus, and Mucor racemosus.[11]

Processing

Natto wrapped in rice straw[12]

Traditionally, natto was made by wrapping cooked soybeans in rice straw, which served as a natural source of B. subtilis spores.[11] Before use, the straw was typically boiled for 15 minutes to reduce unwanted microbes while preserving the heat-resistant B. subtilis spores.[13] Steamed soybeans were then placed inside the straw after cooling and incubated at around 40°C for 24 hours, allowing the spores to germinate and ferment the sugars in the soybeans to transform them into natto.[14] In the early 20th century, scientists were able to isolate B. subtilis from rice straw, leading to more standardized and hygienic production.[13] Therefore, the rice straw has now been replaced with sterile containers, and pure B. subtilis cultures are added directly to sterilized soybeans to produce natto.[11]

Today, the main steps for making commercial natto are: washing, soaking, steaming, fermentation, and maturation. Soybeans are first sorted to remove damaged beans and foreign materials, then thoroughly rinsed to eliminate any dirt or fine particles clinging to their surfaces.[11] While soybean size varies, smaller beans are commonly used for natto. Cleanly washed soybeans are soaked in water for 10–12 hours to ensure adequate moisture absorption, which allows for more uniform cooking during steaming.[8] After the process of soaking, hydrated soybeans are steamed in a pressure cooker. This not only softens the beans but also destroys any residual bacteria on the surface, creating an ideal environment for B. subtilis to access nutrients and release enzymes for fermentation.[11] The steamed beans are cooled before they are inoculated with B. subtilis, portioned into small polystyrene (Styrofoam) trays, and incubated at 40–42°C for 18–24 hours.[7][11] The humidity should be initially maintained at 85-90%, then reduced to 75% after 16 hours.[11] Following fermentation, the natto is cooled within four hours to 10°C or below to limit the production of ammonia and stored at 0–5°C for 1–2 days for maturation.[11] The final product is a slime-coated product in which the beans remain visible and separate.

Packaging and Storage

Natto packaged in a small polystyrene tray[15]

Proper packaging and storage are essential for preserving natto’s distinctive umami flavour and stringy texture. As mentioned previously, natto is commonly packaged in small individual polystyrene trays that insulate against temperature swings.[7] With each containing 30–50 grams of natto, these trays are heat-sealed with a thin plastic film to prevent contamination from external microorganisms, minimize moisture loss, and maintain a semi-anaerobic environment.[11] An alternative packaging method for natto is micro-perforated lidding films, a type of modified atmosphere packaging that regulates gas exchange to allow excess carbon dioxide to escape while limiting oxygen entry.[16] This can slow spoilage and thus extend shelf life of the natto.

Typically, natto has a shelf life of about 7–12 days when stored below 10°C, which helps slow the growth of B. subtilis and enzymatic activity.[11] For long-term storage, natto can be frozen at –18°C to retain its quality for several months.[11]

Regulations and Safety Guidelines

Natto, as well as other imported food, must meet Canadian food safety standards when imported or sold. Under the Safe Food for Canadians Regulations, importers are required to obtain a license, ensure products are traceable, and comply with proper labeling in both English and French.[17] The product must be transported at 4°C or lower to prevent bacterial growth, and any imported natto may be inspected by the Canadian Food Inspection Agency for compliance with safety and quality requirements.[17]

Safety concerns with natto mainly involve microbial contamination during production or storage. Harmful bacteria such as Clostridium perfringens and Bacillus cereus can grow if soybeans are improperly processed.[11] To reduce risk, it is recommended to use commercial starter cultures instead of traditional rice straw, which can carry unwanted microbes. Cooking soybeans under pressure (15–20 psi) for 20–30 minutes eliminates most pathogens, followed by rapid cooling to 10°C or below within four hours.[11] By following these regulations and control points, natto can be safely imported and consumed.

Types of Natto

Hikiwari natto[18]

There are four main types of natto, each with distinct characteristics:[19][20]

  1. Itobiki natto, or stringy natto, is made by fermenting whole steamed soybeans with natto bacteria. It is the most common type of natto found in supermarkets. The name stringy natto refers to the sticky strings that form when the beans are mixed well. Commercially sold versions often include tare sauce and mustard, though nutritional analyses typically exclude these condiments.
  2. Hikiwari natto, or ground natto, is a variant of itobiki natto made from crushed soybeans with the skin removed. Because of the smaller size and lack of skin, it is easier to digest and slightly higher in nutrients than regular itobiki natto.
  3. Goto natto is a traditional type of natto from the Yonezawa area of Yamagata Prefecture. It is made by adding koji, or rice malt, and salt to itobiki natto, then allowing further fermentation. This natto can be eaten without any seasoning, as it has a strong umami flavour from the added salt and fermentation.
  4. Tera natto, or temple natto, originates from Kyoto. It is produced by malting the soybeans that are used for itobiki natto, salting, maturing, and finally drying them. Depending on the product, the final water and salt content can vary.

Potential Exam Question

Question: Which of the following is/are required for the fermentation of soybeans into traditional natto? (Select ALL that apply)

A. Cooked soybeans

B. Ethanol

C. A pure culture of Bacillus subtilis natto

D. An environment with the right temperature and humidity for Bacillus subtilis natto to grow

E. Sugar

Correct Answers: A, C, D

Explanation: Cooked soybeans are required because natto is made from fermented soybeans. A pure culture of Bacillus subtilis natto is also essential because it serves as the starter culture responsible for the fermentation of soybeans into traditional natto. In addition, the fermentation process requires a warm and humid environment to support the optimal growth and metabolic activity of the bacteria, ultimately resulting in the final product. Ethanol and sugar are not the ingredients used in the traditional natto fermentation process.

Why this question should be on the final exam: This question connects our project directly to what we learned in Lesson 9.3 – Fermentation, specifically regarding some of the essential components required for food fermentation: raw materials, a specific microbial starter culture, and appropriate environmental conditions to support microbial growth.

References

  1. ↑ 1.0 1.1 Chan, E.W.C.; Wong, S.K.; Kezuka, M.; Oshiro, N.; Chan, H.T. (May 30, 2021). "Natto and miso: an overview on their preparation, bioactive components and health-promoting effects". Food Research. 5 (3): 446–452. line feed character in |title= at position 75 (help)
  2. ↑ 2.0 2.1 Shurtleff, William; Aoyagi, Akiko (February 15, 2012). "History of Natto and Its Relatives (1405-2012)". SoyInfo Center. Retrieved August 4, 2025.
  3. ↑ "Learn about Japan's Unique Superfood, Natto". Japan National Tourism Organization. August 2, 2022. Retrieved August 4, 2025.
  4. ↑ yoppy (January 27, 2007). "おれのダイエット食(1)". Flickr. Retrieved August 4, 2025.
  5. ↑ 5.0 5.1 Afzaal, Muhammad; Saeed, Farhan; Islam, Fakhar; Ateeq, Huda; Asghar, Aasma; Shah, Yasir Abbas; Ofoedu, Chigozie E.; Chacha, James S. (October 21, 2022). "Nutritional Health Perspective of Natto: A Critical Review". Biochemistry Research International.
  6. ↑ 6.0 6.1 Wang, Chunfang; Chen, Jinpeng; Tian, Wenguo; Han, Yanqi; Xu, Xu; Ren, Tao; Tian, Chengwang; Chen, Changqing (May 26, 2023). "Natto: A medicinal and edible food with health function". Chinese Herbal Medicines. 15 (3): 349–359.
  7. ↑ 7.0 7.1 7.2 7.3 Stanton, W.R.; Owens, J.D. (2003). Encyclopedia of Food Sciences and Nutrition (Second Edition). Academic Press. pp. 2344–2351.
  8. ↑ 8.0 8.1 Guo, Mingruo (2009). Functional Foods: Principles and Technology. Woodhead Publishing. pp. 237–277. ISBN 978-1-84569-592-7.
  9. ↑ Kubo, Yuji; Rooney, Alejandro P.; Tsukakoshi, Yoshiki; Nakagawa, Rikio; Hasegawa, Hiromasa; Kimura, Keitarou (September 8, 2011). "Phylogenetic Analysis of Bacillus subtilis Strains Applicable to Natto (Fermented Soybean) Production". Applied and Environmental Microbiology. 77 (18): 6463–6469.
  10. ↑ Su, Yuan; Liu, Chuan; Fang, Huan; Zhang, Dawei (September 3, 2020). "Bacillus subtilis: a universal cell factory for industry, agriculture, biomaterials and medicine". Microbial Cell Factories. 19.
  11. ↑ 11.00 11.01 11.02 11.03 11.04 11.05 11.06 11.07 11.08 11.09 11.10 11.11 11.12 11.13 11.14 11.15 McIntyre, L.; Yang, T. (December, 2024). "Assessing risks in fermented food processing practices and advice on how to mitigate them" (PDF). BC Centre for Disease Control. Retrieved August 4, 2025. Check date values in: |date= (help)
  12. ↑ 森川, 賢太郎 (February 21, 2017). Flickr https://www.flickr.com/photos/65875362@N02/33033106095/. Retrieved August 4, 2025. Missing or empty |title= (help)
  13. ↑ 13.0 13.1 Petre, Alina (April 9, 2025). "Why Natto Is Super Healthy and Nutritious". Healthline. Retrieved August 4, 2025.
  14. ↑ Batt, Carl A.; Tortorello, Mary Lou (2014). Encyclopedia of Food Microbiology Second Edition. Academic Press. pp. 846–851. ISBN 978-0-12-384733-1.
  15. ↑ Gleam (May 16, 2004). "これから日本の食卓にあがる、工業的に大量生産された一般的な納豆。メーカーのロゴが入らない形態で撮影しました。". Japanese Wikipedia. Retrieved August 4, 2025.
  16. ↑ "Enhancing Freshness with Micro-perforated Lidding Film". Associated Labels and Packaging. March 14, 2025. Retrieved August 4, 2025.
  17. ↑ 17.0 17.1 "Safe Food for Canadians Regulations". Government of Canada. July 31, 2025. Retrieved August 4, 2025.
  18. ↑ Ocdp (July 27, 2017). "おかめ納豆のひきわり納豆". Wikimedia Common. Retrieved August 4, 2025.
  19. ↑ "納豆の栄養素を成分ごとに徹底解説！ひきわり納豆との違いもご紹介". 株式会社丸美屋. February 17, 2025. Retrieved August 4, 2025.
  20. ↑ "Standard Tables of Food Composition in Japan, 2020" (PDF). Ministry of Education, Culture, Sports, Science and Technology, Japan. Retrieved August 4, 2025.
This Food Science resource was created by Course:FNH200.
Retrieved from "https://wiki.ubc.ca/index.php?title=Course:FNH200/Projects/2025/Natto&oldid=869003"