What is a fermented food?
In the past, the majority of scientists believed that fermentation was merely the conversion of biological material generated by a chain of spontaneous chemical reactions occurring one after the other. It was not until Louis Pasteur, a French chemist and microbiologist (1822-1895), that the process of fermentation was considered to involve living matter. Nowadays, it is well known that fermentation is the breakdown of biological compounds mediated by microorganisms like bacteria and fungi, and their enzymes.
Fermentation is widely used in the food industry (for instance cheese and bread production or the production of some traditional foods) but there are also several other industries that make use of the process (including for the production of ethanol, drugs like antibiotics, treatment of sewage).
Fermentation is a food processing technique widely used across the globe for millennia. The major reasons to ferment food are:
• To extend shelf life
• To increase food safety or to avoid contamination
• To vary the taste, digestability and consistency
• To improve the nutritional value (bioavailability of amino acids, isoflavones, vitamins etc)
Even if they did not know exactly what was behind the processing, the Egyptians were fermenting food during the 4th millennium BC. They brewed beer, produced wine and baked bread with at that time undiscovered microorganisms.
Furthermore, in ancient Greece, fermented milk products were appreciated, especially cheese. In an interesting way, Homer describes in his epic poem ‘The Odyssey’ how to produce feta cheese by acidification of milk from sheep and goats.
In Asia, a tradition of fermenting vegetables or tea leaves has been taking place for many centuries. A cheese-like product originating in China, Sufu (Furu), is reported to exist at least since the Wei Dynasty in China (220–265 BC). Literally translated, Sufu means “moulded milk” and it is produced from the fermentation of soybeans.
The popularity of fermented food has increased in the recent years across the globe. Consumers interested in a healthy diet are attracted because of their potential benefits, especially by their possible role in improving the functioning of the gut.
Do all fermented foods contain live microbes?
Fermented foods must undergo a microbial conversion, either naturally or through the addition of a starter culture. However, some products may be treated (pasteurised, baked, or filtered) in a way that ultimately kills any live microbes before we consume them.
For example, sourdough. When the dough is used to make bread it will be baked, and this exposure to heat will kill the microbes. Some yoghurts are also heat treated, especially if fresh fruits have been added.
As well, some fermented vegetables are packaged in jars and may be heat treated as a means of extending its shelf life. This may not always be the case, so it is important for consumers to read the label to see if it is a source of active microbes.
For more information on fermented foods visit: https://isappscience.org/fermented-foods/
Are there any health benefits of consuming fermented foods?
Fermented foods have been consumed for thousands of years but have regained popularity recently in Western diets. This is partly because fermentation can change the foods taste, texture and digestibility but also because people are interested in their health-promoting potential (Marco et al. 2017).
Fermented foods and approved health claims
Fermented dairy products in particular have received attention for their potential benefits, and in fact live yoghurt has a European Food Safety Authority approved health claim (EFSA 2010), stating that ‘live yogurt cultures in yogurt improve digestion of yogurt lactose in individuals with lactose maldigestion’. In order to use this claim, the product should contain at least 108 colony forming units (CFU) of the live starter microorganisms (Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus) per gram.
Fermented foods around the world
Here we share with you some examples of popular fermented foods
(Table 1) followed by a brief introduction to some fermented foods with a rich cultural heritage behind them.
Table 1: Examples of fermented foods (adapted from Chilton et al. (2015) Nutrients 7(1): 390-404)
Kefir is a viscid and tart-like food that originated from the Caucasus region. For the fermentation, cow milk was originally mixed together with the so-called kefir nodule: a community of different bacteria and yeasts (Lactobacillus, Lactococcus, Streptococcus, Leuconostoc, Saccharomyces, Kluyveromyces, Candida). The exact composition of these nodules varied depending on the region and season, and they have a different effect on the resulting taste of the kefir. Today strictly defined starter cultures are used.
Kimchi belongs to the daily Korean menu. Basically, all kind of vegetables that have been fermented with lactic acid bacteria are called Kimchi. The most widely used ingredients are Chinese cabbage or radish but every Korean family has their own traditional recipe and their very own mix of spices.
Lactic acid bacteria that have been isolated from fermented kefir or kimchi produce considerable amounts of antimicrobial substances effective against bugs like Listeria monocytogenes or Salmonella typhimurium.
Idli is a breakfast food produced from the fermentation of rice (Oryza sativa) and black gram dhal (Phaseolus mungo). The fermented dough is consumed after steaming and is a popular dish in India and Sri Lanka. The mainly active microorganisms from Idli are the lactic acid bacteria Leuconostoc mesenteroides, Lactobacillus delbrueckii, Lactobacillus fermentum, Lactobacillus lactis, and Streptococcus faecalis.
During the production of Idli, the lactic acid bacteria do not only produce lactic acid but also carbon dioxide. As a result, the dough is loose and the low-oxygenic conditions of the fermentation process are improved. The content of soluble vitamins (B1, B2 and B12), folic acid, as well as the release of essential amino acids (lysine, cysteine, and methionine) increases during the fermentation of Idli improving its nutritional value.
Miso soups are well-known in Japanese restaurants. Miso is prepared from the fermentation of soybeans (Glycine max) together with rice (Oryza sativa), oat (Avena sativa) or wheat (Triticum aestivum). Fermented soy foods such as miso contain isoflavones, which have an anti-oxidant effect.
Chilton et al. (2015) Inclusion of Fermented Foods in Food Guides around the World. Nutrients 7(1): 390-404
EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA); Scientific Opinion on the substantiation of health claims related to live yoghurt cultures and improved lactose digestion (ID 1143, 2976) pursuant to Article 13(1) of Regulation (EC) No 1924/2006. EFSA Journal 2010;8(10): 1 763. [18 pp.]. Available online: https://efsa.onlinelibrary.wiley.com/doi/epdf/10.2903/j.efsa.2010.1763
Marco et al. (2017) Heakth benefits of fermented foods: microbiota and beyond. Current Opinion in Biotechnology 44:94 -102