Examples of fermented food The range of health benefits of fermented foods
The synthesis of nutritive and bioactive compounds
Addition of commensal microbes to the gastrointestinal tract
Probiotic characteristics of fermented food microorganisms
References
Further reading

Fermented food or food fermentation is a food processing technology that harnesses the growth and metabolic activity of microorganisms for the stability and transformation of food. Historically, fermentation was predominantly utilized for stabilizing perishable agricultural products. Since then, technology has evolved to widen the utility of food fermentation beyond preservation, to produce organoleptic, functional, and nutritional characteristics in food.

Fermented food products comprise a significant component of diets in developing countries, and there has recently been renewed interest in fermented food products driven by supported health benefits. It is projected that this trend will continue to rise as a consequence of the increasing prevalence of metabolic syndrome (obesity, allergies, and intolerances, encompassing lactose, gluten, nut, etc.), alongside shifting patterns in lifestyle choices to include veganism and vegetarianism.

Examples of fermented food

Fermented foods exact their effects through several mechanisms of action, including their impact on the body's microbiota. There is mounting evidence for the effects on gastrointestinal health and disease in humans. Of the fermented food groups, evidence for the effects of dairy-based products such as yogurt and cheese has been extensively reviewed.

Other common foodstuffs more prevalent in the East include kombucha, sauerkraut, tempeh, natto, miso, kimchi, and sourdough. Below outlines the basis of these fermented foods alongside an example of the bacterial starter culture used to produce them.

• Kefir: This is a fermented milk beverage that originates in the Caucasus, and the source of microorganisms used to produce it originates from a starter culture. The microorganisms identified in the final product include Lactobacillus kefiri, Lactobacillus paracasei, Lactobacillus parabuchneri, Lactobacillus casei, Lactobacillus lactis, Lactococcus lactis, Acetobacter lovaniensis, Kluyveromyces Lactis, Saccharomyces cerevisiae
• Kombucha is a fermented tea beverage from China, and the source of microorganisms used to produce it originates from a starter culture. The microorganisms identified in the final product include Komagataeibacter xylinus, Saccharomyces cerevisiae, Zygosaccharomyces bailii. Brettanomyces bruxellensis, Acetobacter pasteurianus, Acetobacter aceti, Saccharomyces cerevisiae, Zygosaccharomyces bailii, Brettanomyces bruxellensis, Acetobacter xylinum, Zygosaccharomyces spp., Acetobacter, Gluconacetobacter
• Sauerkraut is fermented cabbage that originated in China. The source of microorganisms is spontaneous
• Natto is a fermented soybean that originated in Japan. The starter culture includes bacillus subtilis
• Miso is a form of fermented soybean paste which originated in Japan. The starter culture is aspergillus oryzae
• Kimchi is a fermented vegetable dish from Korea. The starter culture is spontaneous
• Sourdough bread is bread produced from a longer fermenting. And originates from the Middle East and Europe. The starter culture is spontaneous or ‘back slopping,’ a fermentation technique in which a small quantity of the previous fermentate is used as the raw material for the next fermentation step

The range of health benefits of fermented foods

Fermented foods have a reduced risk of contamination as they are enriched in antimicrobial end-products. These end-products include organic acids, ethanol, and bacteriocins. Other non-health-related effects of fermentation include the introduction of desirable tastes and textures that differs substantially from those present in the starting food. For example, fermented olives typically result in microbial-induced removal of bitter-tasting phenolic compounds.

Fermented foods also have characteristics known to promote human health; these characteristics are not attributed to the basic nutrition present in the starting food.

Large cohort investigations have demonstrated a strong correlation between the consumption of fermented dairy food and the ability to maintain weight. In addition, long-term prospective studies have also shown the capability of fermented foods to reduce the risk of cardiovascular disease, overall mortality, and type 2 diabetes, as a result of increased yogurt consumption.

The benefits produced from yogurt consumption are thought to be a result of immediate physiological responses. This is indicated by improved glucose metabolism following fermented milk consumption and reduced muscle soreness induced by resistance exercise. To support the role of fermented foods in metabolism, there is evidence to suggest the anti-diabetic and anti-obesity benefits of kimchi.

In addition, fermented foods play a fundamental role in conditions associated with inflammation. In immune-related pathologies such as inflammatory bowel disease, arthritis, and sclerosis, there is evidence to suggest the role of decreasing the inflammatory response induced by the consumption of fermented foods; however, clinical data has not yet been reported. 

Fermented foods also produce a probiotic effect, changing the proportion of microbiota in the gastrointestinal tract by introducing microbial species.

The synthesis of nutritive and bioactive compounds

Fermentation results in the formation of new compounds which can modulate health. One of these components includes lactic acid; this has been recently shown to reduce pro-inflammatory cytokines and secretion of toll-like receptor activated, bone marrow-derived macrophages, and dendritic cells depending on the dose. Lactate can modify the redox status by altering the quantities of reactive oxygen species in intestinal cells. 

While lactic acid is relatively high in quantity, other microbial-derived compounds produced during fermentation are usually dependent on the strain of bacteria. The B vitamins, which include folate, B12, and riboflavin, are produced from several non-vitamin precursors by dairy and plant foods bacteria.

Amino acids and their derivatives exert functional effects in immunomodulation and neurotransmission and are also produced during fermentation. Some secretions may also possess antioxidant activity (proteins and exopolysaccharides), prevent pathogenic adhesion to the intestinal mucosa, or confer hypocholesterolemic or immune stimulatory activity. Polysaccharides produced may also act as prebiotics, providing input material for producing short-chain fatty acids by the intestinal microbiota.

Addition of commensal microbes to the gastrointestinal tract

The hallmark distinction of fermented foods relative to their fresh counterparts is the presence of viable microorganisms. Fermented foods, most prominently sauerkraut, kimchi, yogurt, kefir, cheese, kombucha, miso, and dry fermented sausage, contain viable microbial cells ranging between  10⁶ and 10⁹ cells/g or cells/ml. A fraction of these microbes can reach the human digestive tract. The addition of fermented foods to the diet serves as a potential source of microbial consumption, increasing the number of microbes in the diet by 10,000. These microbes are already sizable yet transient means of increasing the intestinal microbiota.

This is particularly impactful in western societies, where highly processed and sanitized foods limit microbial entry. This hygiene hypothesis suggests start exposure to microbes is essential for developing the immune system, alongside neural function. Therefore, by consuming fermented foods, an indirect means of circumventing this sterility is presented.

Probiotic characteristics of fermented food microorganisms

Bacterial species found in fermented foods are similar to the species that generally promote gastrointestinal tract health. This concept is consistent with the emerging perspective that the health benefits of probiotic cultures can be attributed to a certain bacterial species rather than a specific strain of a specific species. Consequently, when fermented foods contain large numbers of live cells belonging to a species known for health benefits, they should be considered to have similar benefits to those found by probiotic bacteria of the same species.

Similar to existing probiotic strains, microbes from fermented foods could produce the same effects on intestinal epithelial, immune, and enteroendocrine cells – which until recently had been attributed to specific strains. However, the impact of the changes produced by fermentation-associated microorganisms and the importance of their probiotic efficacy is contested.  

Fermented foods are becoming increasingly recognized as playing a role in human health. Therefore, fundamental research is necessary to complement existing research on the fermentation-associated strains; this will aid in determining the core properties expressed as they relate to the transformation of compounds in foods, the production of additional compounds, and the impact on the host-microbe interactions in the gastrointestinal tract.

References

• Dimidi E, Cox SR, Rossi M, et al. (2019) Fermented Foods: Definitions and Characteristics, Impact on the Gut Microbiota and Effects on Gastrointestinal Health and Disease. Nutrients. doi:10.3390/nu11081806.
• Marco ML, Heeney D, Binda S, et al. (2017) Health benefits of fermented foods: microbiota and beyond. Curr Opin Biotechnol. doi:10.1016/j.copbio.2016.11.010.

Further Reading

• All Food Content
• Health Benefits of Chia Seeds
• What are Functional Foods?

Written by

Hidaya Aliouche

Hidaya is a science communications enthusiast who has recently graduated and is embarking on a career in the science and medical copywriting. She has a B.Sc. in Biochemistry from The University of Manchester. She is passionate about writing and is particularly interested in microbiology, immunology, and biochemistry.