What is vitamin K2 extracted from?

While most people are familiar with vitamin K1 from leafy greens, a lesser-known fact is that vitamin K2 is primarily a product of bacterial synthesis. This unique fat-soluble nutrient, vital for bone and heart health, is extracted from specific fermented foods and certain animal products.

Quick Summary

Vitamin K2 is a fat-soluble nutrient sourced mainly from fermented foods, including natto and certain cheeses, and some animal products. Supplement-grade K2, particularly the MK-7 form, is commercially produced through microbial fermentation, notably using the bacterium Bacillus subtilis var. natto.

Key Points

• Bacterial Origin: Unlike vitamin K1 from plants, vitamin K2 is naturally synthesized by bacteria, and its production is key to both food-based and supplement-based sources.

• Natto is a Key Source: The traditional Japanese fermented soybean dish, natto, is the richest dietary source of K2 (specifically MK-7) due to fermentation by Bacillus subtilis.

• Commercial Production by Fermentation: For supplements, MK-7 is efficiently produced through large-scale microbial fermentation using select Bacillus strains under carefully controlled conditions.

• Extraction Process: The extraction of K2 from fermented broth involves multi-step processes including cell separation, cell wall disruption, solvent extraction, and purification to obtain a high-purity product.

• MK-4 vs. MK-7: The two most common forms, MK-4 and MK-7, have different origins; MK-4 is animal-derived, while MK-7 is primarily bacterially derived and has a longer half-life in the body.

• Food Variety Matters: Dietary K2 comes from a variety of sources, including fermented foods (natto, certain cheeses) for MK-7 and animal products (liver, eggs) for MK-4.

• Biotechnology Advances: Modern genetic and metabolic engineering techniques are being developed to create even more efficient microbial cell factories for K2 production.

The Bacterial Origin of Vitamin K2

Contrary to the plant-based origin of vitamin K1, vitamin K2 (menaquinone) is predominantly synthesized by bacteria. This microbial origin is the key to understanding where the nutrient is sourced. It is not naturally present in large quantities in most Western diets, which is why supplementation and consumption of specific fermented foods are important for maintaining adequate levels. There are several forms of vitamin K2, distinguished by the length of their side chain and denoted as MK-n (e.g., MK-4, MK-7, MK-9).

Key Natural Food Sources

Dietary sources of vitamin K2 can be broadly categorized into fermented foods and animal products. The bacterial action during fermentation is responsible for the high K2 content in foods like cheese and natto. The amount and type of menaquinone can vary greatly depending on the specific bacteria and fermentation process used.

• Natto: This traditional Japanese dish of fermented soybeans is, by far, the richest dietary source of vitamin K2, specifically the highly bioavailable MK-7 form. The fermentation is carried out by the bacterium Bacillus subtilis var. natto, and levels can reach over 1,000 micrograms per 100 grams.
• Cheeses: Certain aged and fermented cheeses contain significant levels of longer-chain menaquinones, such as MK-8 and MK-9. Examples include Gouda, Edam, and hard cheeses, with the bacterial starters playing a crucial role in their production.
• Animal Products: Some animal products contain the MK-4 form of vitamin K2, which is synthesized in animal tissues through the conversion of vitamin K1. Good sources include goose liver pâté, certain chicken parts (dark meat and liver), egg yolks, and high-fat dairy from grass-fed animals.

Commercial Extraction for Supplements

For mass-market supplements, natural sourcing from foods is inefficient and costly. Therefore, a robust industrial process is used, relying on controlled microbial fermentation.

1. Microbial Fermentation: The primary commercial method for producing MK-7 is large-scale microbial fermentation. Specialized, high-yielding strains of Bacillus subtilis are cultured in bioreactors under optimized conditions to maximize MK-7 production. The bacteria produce the menaquinone as a metabolite during their growth phase.

2. Downstream Processing and Extraction: After fermentation is complete, the valuable MK-7 must be separated and purified from the bacterial culture. This multi-step process involves several stages.

   • Cell Separation: The bacterial cells (or thalli) are separated from the fermentation broth, often using methods like ultrafiltration and centrifugation.
   • Cell Wall Disruption: Since a significant portion of the MK-7 is trapped within the bacterial cell membrane, techniques like thermo-acidic extraction or treatment with enzymes are used to break open the cell walls.
   • Solvent Extraction: Organic solvents, such as ethanol and hexane, are used to extract the fat-soluble MK-7 from the broken cells and the medium.
   • Purification and Crystallization: The extracted crude product undergoes further purification steps, such as chromatography, to remove impurities. Finally, crystallization yields a high-purity vitamin K2 crystal for use in supplements.

Comparison of MK-4 and MK-7 Extraction

Feature	MK-4	MK-7
Primary Source	Conversion from Vitamin K1 in animal tissues and dietary animal products (e.g., eggs, liver, butter).	Bacterial fermentation, especially Bacillus subtilis var. natto, and found in fermented foods.
Commercial Production	Typically produced via chemical synthesis from geraniol and isophytol, or from vitamin K1, for supplements.	Primarily produced via large-scale microbial fermentation using bacterial strains like Bacillus subtilis.
Side Chain Length	Shorter chain of 4 isoprenoid units.	Longer chain of 7 isoprenoid units.
Half-Life	Short half-life in the body, which requires more frequent dosing for supplements.	Long half-life, making it effective with once-daily dosing.
Absorption	Less readily absorbed compared to MK-7.	Absorbed more efficiently, with higher bioavailability for extrahepatic tissues.

Conclusion

In summary, the extraction of vitamin K2 is a sophisticated process that leverages nature's microbial ability to synthesize menaquinones. While traditional food sources like natto provide potent, natural MK-7, commercial production for supplements relies on advanced microbial fermentation technology using specific Bacillus strains. Understanding these sources and extraction methods is vital for both supplement manufacturers and health-conscious consumers. By utilizing these processes, companies can provide a consistent and bioavailable source of this crucial nutrient to support public health initiatives for bone and cardiovascular well-being.

For more in-depth information on the production of vitamin K by microorganisms, researchers can refer to detailed scientific reviews, such as the one published in the International Journal of Molecular Sciences.

Frequently Asked Questions

Which bacteria produce vitamin K2?

A wide variety of bacteria produce vitamin K2, most notably the Bacillus species. The bacterium Bacillus subtilis var. natto is particularly well-known for producing high levels of menaquinone-7 (MK-7) during the fermentation of soybeans.

Can humans produce their own vitamin K2?

Yes, bacteria in the human gut can synthesize some vitamin K2. However, the absorption from the distal colon, where most of this production occurs, is generally thought to be minimal and contributes little to the body's overall needs.

Are there different types of vitamin K2?

Yes, vitamin K2 exists as several subtypes, known as menaquinones (MK-n). These are distinguished by the length of their isoprenoid side chains, with MK-4 and MK-7 being the most well-known. Their side chain length affects their bioavailability and half-life in the body.

How are vitamin K2 supplements made?

Commercially, vitamin K2 supplements, especially MK-7, are produced using controlled microbial fermentation. High-yielding bacterial strains, typically Bacillus subtilis, are grown in large bioreactors, after which the MK-7 is extracted, purified, and formulated into supplements.

Is all vitamin K2 sourced from bacteria?

While the potent MK-7 form is bacterially derived, another important form, MK-4, is found in animal products and is also synthesized in animal tissues from dietary vitamin K1. Thus, K2 comes from both bacterial synthesis and animal conversion.

Which food is the best source of vitamin K2?

The Japanese fermented soybean product, natto, is the richest known dietary source of vitamin K2 (specifically MK-7). Other sources include certain fermented cheeses and animal products like liver and egg yolks, though with lower concentrations.

Why is microbial fermentation preferred for commercial K2 production?

Microbial fermentation allows for the production of specific, highly bioavailable forms of K2 like MK-7 in a controlled and scalable manner. It is often more sustainable and can produce a higher yield compared to extracting from natural food sources.