What is Vitamin K2 and How is it Produced?
Vitamin K is a fat-soluble vitamin essential for several physiological processes, including blood clotting and bone metabolism. It exists in two main forms: K1 (phylloquinone), found primarily in leafy greens, and K2 (menaquinones), mainly found in animal products and fermented foods. The K2 in fermented foods is a direct byproduct of bacterial metabolism. Unlike the K1 naturally present in fresh cabbage, the K2 is synthesized during fermentation by the action of specific bacteria, most notably lactic acid bacteria (LAB).
During fermentation, microbes such as Lactococcus species and Propionibacteria convert the raw material into new compounds. These bacteria, which are used to ferment milk and vegetables, possess the metabolic pathways to produce menaquinones, the compounds that make up vitamin K2. The specific forms of K2 produced can vary. For instance, Bacillus subtilis, used to make natto, is a prolific producer of the MK-7 form, while some LAB strains produce MK-8 and MK-9.
Factors Influencing K2 Content in Fermented Cabbage
The amount of K2 in fermented cabbage is not static. Several key factors can significantly influence the final concentration of menaquinones:
- Bacterial Strains: The type of bacteria used for fermentation is the most critical factor. Different strains of LAB have different capacities for producing K2. Some starter cultures are specifically selected for their higher yield of K2.
- Fermentation Time: Extending the fermentation time can increase the yield of K2. A longer fermentation period allows the K2-producing bacteria to multiply and synthesize more menaquinones.
- Temperature and Oxygen Levels: Research has shown that temperature and the presence of oxygen (aeration) during fermentation can alter both the quantity and specific forms of K2 produced. Some studies suggest that aerobic fermentation can lead to a shift towards longer-chained menaquinones.
- Other Ingredients: The addition of different carbon sources during fermentation can also affect K2 production. For example, some studies on fermented dairy products found that using fructose resulted in higher vitamin K2 content compared to glucose.
How much K2 is in fermented cabbage?
Based on various studies, the K2 content in typical fermented cabbage products like sauerkraut is modest when compared to other sources but is a meaningful addition to a healthy diet. Reports suggest a half-cup serving (around 70-75 grams) can contain between 2.75 and 6 micrograms (mcg) of Vitamin K2. In contrast, a 100-gram serving of the Japanese fermented soybean dish, natto, can contain over 1,000 micrograms of K2 (MK-7).
Comparison of K2 Sources
To put the K2 content of fermented cabbage into perspective, consider a comparison with other common food sources. The following table highlights the significant variation in K2 concentration across different foods.
| K2 Source | Typical K2 Content (per serving) | Key K2 Form | Notes |
|---|---|---|---|
| Natto (fermented soybeans) | 1,000+ mcg (per 100g) | MK-7 | Richest source of K2, though taste may not appeal to all. |
| Fermented Cabbage (sauerkraut) | ~2.75–6 mcg (per half-cup) | Variable (often MK-8, MK-9) | Content varies based on fermentation process. |
| Hard Cheeses (e.g., Gouda) | ~75 mcg (per 100g) | MK-9 | Aged cheeses are a notable source of K2. |
| Egg Yolk (from grass-fed chicken) | ~15.5 mcg (per yolk) | MK-4 | Higher content if chickens are pasture-raised. |
| Butter (from grass-fed cows) | ~15 mcg (per 100g) | MK-4 | As with eggs, content depends on the animal's diet. |
Health Benefits of K2 from Fermented Foods
Including fermented cabbage and other sources of vitamin K2 in your diet offers several potential health benefits:
- Supports Bone Health: Vitamin K2 activates proteins like osteocalcin that help bind calcium to the bone matrix, promoting higher bone mineral density and reducing fracture risk, especially in postmenopausal women.
- Promotes Heart Health: K2 helps prevent the calcification of arteries by activating matrix Gla protein (MGP), which inhibits calcium buildup in blood vessels. This contributes to better cardiovascular health and reduced risk of heart disease.
- Enhances Dental Health: The same osteocalcin activation that benefits bones also plays a role in dental health, aiding in the mineralization of dentin and enamel.
- Improves Gut Health: As a fermented food, cabbage provides probiotics that support a healthy gut microbiome. A balanced gut can not only aid digestion but may also help the body produce its own K2.
Conclusion
Fermented cabbage provides a modest but variable amount of vitamin K2, which is synthesized by lactic acid bacteria during the fermentation process. While not as potent a source as natto, it offers meaningful levels of K2, which is vital for bone and heart health. The specific K2 content is influenced by factors such as bacterial culture, fermentation time, temperature, and aeration. Incorporating fermented cabbage into a balanced diet, alongside other fermented foods and animal products, contributes to overall health by providing beneficial probiotics and a valuable, naturally produced dose of vitamin K2. For individuals seeking to maximize their K2 intake, considering more concentrated sources or exploring longer fermentation techniques may be beneficial. For more information, the National Institutes of Health provides extensive resources on vitamin K and its functions.
