(Mar.22-Sep.24, 2022, Nagoya University Museum)
Special Display 3
The term “lactic acid bacteria” dates from 1857, when Louis Pasteur discovered the presence of microorganisms in soured milk and gave them this name. The current definition of “lactic acid bacteria” is microorganisms that ferment sugars to produce lactic acid and other organic acids, and does not indicate any specific group of microbes in microbiological taxonomy. Lactic acid bacteria are taxonomically scattered among several genera.**
In consuming fermented foods, the function of lactic acid bacteria as defined above is very important to us humans. This is because lactic acid bacteria produce lactic acid and other organic acids for us. When these build up in food, the environment within that food is exposed to acidity. Under acidic conditions, the growth of microorganisms harmful to humans is suppressed. To the degree that fermentation by lactic acid bacteria continues, that food can be anticipated to be edible. This makes long-term usage of that food possible.
In addition, the lactic acid bacteria themselves are living things, so they retain vitamins and polysaccharides, and are thought to contribute to the sustenance of human health. Vitamins are nutrients essential for our bodies’ maintenance but cannot be produced within our bodies, so they need to be obtained through food intake. Even if these vitamins are not present in the original food ingredients, lactic acid bacteria can produce them for us. Polysaccharides are known to contribute to immune strength and defense against diseases. Lactic acids and other organic acids have their own different flavors. It is thought they may contribute to food culture, i.e., the enjoyment of flavors.
In natural fermentation, it is very important for us humans to be able to reproduce identical fermented foods each time. Even though a certain degree of knowhow is needed, if the same product cannot be made each time, that knowledge will not be transmitted to subsequent generations and the product will not be recorded in history as a fermented food. Let us consider yogurt for an example. Lactic acid bacteria in milk break down the sugars, releasing lactic acid and other organic acids into the milk. As a result, the milk’s acidity rises little by little. Since the kinds of microbes that can grow in an acidic environment are limited, lactic acid bacteria become the dominant species in the milk, and the result is yogurt.
* The English title has slightly been changed from the panel.
** “Genus” (plural, “genera”) is a unit for groups of closely related species. The first name of a binomial scientific name indicates the genus (e.g., the genus of Lactococcus lactis, a lactic acid bacteria species, is “Lactococcus”).
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