Lactic acid is a metabolic waste product and is responsible for the burning sensation in your muscles when you're working hard. Additionally, however, it's a common component of many foods because it occurs naturally when food has been fermented by bacteria and adds a tangy flavor to fermented foods.
Lactic Acid
Lactic acid is a small molecule made up of carbon, oxygen and hydrogen. It's related to acetic acid, which is the acid in vinegar, and to citric acid, which you find in oranges and many other fruits. Like acetic acid, which occurs in foods primarily as the result of fermentation processes, lactic acid is a metabolic waste product of both animals and many bacteria and occurs in food that bacteria have cultivated, explain Drs. Mary Campbell and Shawn Farrell in their book "Biochemistry."
Fermentation
You, like other animals, produce the majority of your energy by burning nutrient compounds in oxygen. The waste products of this process are carbon dioxide and water. When you produce energy without sufficient oxygen, however, the waste product is lactic acid, which accumulates in muscles and causes a burning sensation. Some bacteria also make lactic acid as a byproduct of energy production. Lactobacillus acidophilus, used to make yogurt, and other similar species are among these, explain Drs. Reginald Garrett and Charles Grisham in their book "Biochemistry."
Fermented Dairy
Lactic acid is most common as part of the human diet in fermented dairy products. Some bacteria can survive in milk and break down the milk sugar, called lactose, for energy. As a byproduct of this reaction, they produce lactic acid. The acid reacts with the proteins in milk, clumping them together. This produces the creamy texture associated with yogurt and can also produce curds, as in cottage cheese. The lactic acid has a sour taste characteristic of yogurt.
Misconceptions
Because lactic acid's name sounds similar to the word "lactose," many people incorrectly assume that if you're lactose intolerant, you have to avoid lactic acid. There's no truth to this; the two molecules are different. Actually, many lactose intolerant individuals are able to consume fermented, lactic acid-containing milk products because bacteria have broken down much of the lactose, leaving behind a mixture that the lactose intolerant individual can digest.
References
- "Biochemistry"; Mary Campbell, Ph.D. and Shawn Farrell, Ph.D.; 2005
- "Biochemistry"; Reginald Garrett, Ph.D. and Charles Grisham, Ph.D.; 2007
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