Some foods, fermented foods, are produced or preserved by the action of microbes, usually yeasts and bacteria. Fermentation is an ancient practice, and results in enhanced taste, nutritional value, preservative, and medicinal properties. There has been widespread fermentation of a great variety of food types, including cereals, dairy, vegetables, fish, seafood and meats, which have all been a significant part of ancestral dietary practices. Examples of fermented foods include those which are fermented by bacteria (e.g. lactobacillus), such as yogurt and sauerkraut, and those which are made by yeasts (e.g. Saccharomyces cerevisiae) fermenting sugar into alcohol or CO2 (e.g. beer, wine, bread).
Other foods made by microbes include a wide variety of milk products (http://www.milkingredients.ca/index-eng.php?id=180 ) such as cheeses, sour cream, crème fraiche and buttermilk, and there is evidence that fermented milk products have been produced sine the 10th century BC. Cocoa bean fermentation is used in some chocolates. The traditional method for making cod liver oil used a method which fermented cod and sea water for up to a year before removing the oil. Kefir is a fermented beverage made from a sugary liquid, such as milk, soy milk or fruit juices which is fermented with kefir grains, which contain a mixture of bacteria and yeasts.
As our knowledge of the human microbiome increases, it is becoming increasingly clear that there are untold connections between our resident microbes and many aspects of physiology. We are also discovering the ways in which fermentation alters foods pre-consumption, and how chemicals produced in fermented foods (e.g. lactoferrin, bioactive peptides) may act on our gut microbes.
The consumption of fermented foods may be particularly relevant to emerging research linking traditional dietary practices and positive mental health. Some traditional foods may help mitigate inflammation and oxidative stress, possibly through our gut microbes. There is also some emerging evidence that suggests that some bacteria, Lactobacillus and Bifidobacteria species, associated with fermented foods may also influence brain health via direct and indirect pathways.
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Please take a see the following graphics, produced by The International Scientific Association for Probiotics and Prebiotics (ISAPP) on Food-related Microbes