Lactic acid bacteria are microorganisms that live everywhere in nature and in ourselves, such as on the skin and in our intestines. Here they perform a number of tasks.
In short, lactic acid bacteria converts carbohydrates into lactic acid and other substances, such as amino acids and vitamins.
Lactic acid bacteria actually feed on the food, nutrients and fibers that our bodies need degraded in order to digest it, and from these foods and nutrients they form new substances that our bodies use for other purposes, such as regulating our pH levels.
The same principle applies when you ferment a product. By adding lactic acid bacteria to the food (or using naturally present bacteria), which then consume carbohydrates and converts them into the organic acids. The organic acids alter the taste and texture, but also lowers the pH to a level at which harmful bacteria cannot thrive.
Therefore, lactic acid bacteria are used to preserve foods and give it a different taste experience. Foods such as salami, olives and yogurt is usually produced by a fermentation process.
Lactic acid bacteria are named so, because they produce lactic acid. They have nothing in itself to do with milk or dairy, and can easily be consumed by people with lactose intolerance.