Lactic acid

Tiny things in our bodies make acid. This acid comes from the food we eat. It can also live in sour milk.

When you run very fast, your body needs energy. Sometimes your body does not have enough air to help. Then, your muscles make this acid to keep going.

Small living things can also make this acid. They turn sugar into acid. This can happen in your mouth. It can cause tiny holes in your teeth.

Doctors use this acid in medicine. They put it in fluids for people who are hurt. It helps them feel better.

This acid is very useful in our world. It can even help make plastic that breaks down easily.

Lactic acid is a special kind of acid. It is white and solid. It also mixes well with water. This acid can be made by people in labs. It can also be made by nature.

Our bodies make lactic acid. This happens when we use our muscles for hard work. When you sprint, your body needs power. Sometimes, there is not enough oxygen for your cells. To keep going, your cells turn sugar into lactate. This is a type of lactic acid. This process helps your body keep making power during exercise.

Tiny living things called bacteria also make this acid. They eat simple sugars like glucose. They turn those sugars into lactic acid. This happens in sour milk. It also happens in your mouth. These bacteria can cause cavities in your teeth.

Lactic acid is very useful today. People use it to make plastic. This kind of plastic is biodegradable. This means it can break down naturally.

Doctors also use it in medicine. They use it in fluids for patients. These fluids help people who have lost blood from injury or surgery.

Lactic acid is a very interesting organic acid. In its solid form, it looks like a white substance. It is also miscible with water, which means it can dissolve easily. When it dissolves, it creates a clear liquid called a colorless solution. This acid is special because it is an alpha-hydroxy acid. This means it has a specific group of atoms near another group. Scientists use it in many different industries to make new things. It is a very important part of both nature and human technology.

Our bodies use lactic acid to keep us moving. When you do intense exercise like sprinting, your muscles need energy fast. Sometimes, your body cannot get enough oxygen to your cells quickly enough. To solve this, your cells use a process called fermentation. An enzyme called lactate dehydrogenase helps turn a substance called pyruvate into lactate. This step is very helpful because it helps your cells keep making energy. This allows you to continue your hard work even when oxygen is low.

Many people have studied this acid over a long time. A Swedish chemist named Carl Wilhelm Scheele first found it in 1780. He found it inside sour milk. The name comes from the Latin word for milk. Later, in 1808, Jöns Jacob Berzelius found it in muscles. He saw that it was made during hard work. In 1856, Louis Pasteur discovered that tiny bacteria help make it. Finally, Johannes Wislicenus worked out its exact structure in 1873.

Lactic acid is produced in huge amounts around the world. In the early 2020s, global production was more than 1.5 million tonnes. This is a big jump from 275,000 tonnes in 2006. Bacteria like Lactobacillus are used to make it from sugars. These bacteria can eat glucose or sucrose to create the acid. In the Soviet Union, leaders invested in these bacteria to make acid more cheaply. Today, companies like NatureWorks LLC make huge amounts of it. One large facility in Blair, Nebraska, can make 140,000 tonnes every year.

We can see the effects of lactic acid in our daily lives. It is used to make biodegradable plastics that break down naturally. This helps reduce waste in our environment. Doctors also use it in special medical fluids for patients. These fluids help people who have lost blood from surgery or injury. You might also find it in your mouth. Bacteria in your mouth eat sugar and make acid. This acid is what causes cavities in your teeth.

Lactic acid is a vital organic acid with the molecular formula C3H6O3. In its solid state, it appears as a white substance. It is miscible with water, meaning it dissolves easily to form a colorless solution. Chemically, it is classified as an alpha-hydroxy acid (AHA). This term describes a molecule where a hydroxyl group sits adjacent to a carboxyl group. This specific structure makes it much more acidic than acetic acid. In fact, it is ten times more acidic because of intramolecular hydrogen bonding. In a solution, the acid can lose a proton to become a lactate ion. This ion is also known as 2-hydroxypropanoate.

Lactic acid is a chiral molecule, which means it exists in two different mirror-image forms called enantiomers. One form is known as (S)-lactic acid, or (+)-lactic acid. The other is (R)-lactic acid, or (−)-lactic acid. When these two forms exist in equal amounts, the mixture is called racemic lactic acid. The specific type of acid produced depends on its source. For example, fermentation of milk often produces a racemic mixture. However, certain bacteria produce only the (S) form. In animal muscles, the (R) enantiomer is produced. This muscle-derived version is sometimes called "sarcolactic" acid, a name taken from the Greek word for flesh.

In the human body, lactic acid plays a critical role in energy metabolism. During intense exercise like sprinting, the demand for energy is very high. Cells break down glucose into a substance called pyruvate. Normally, cells use oxygen to turn pyruvate into energy through the Krebs cycle. However, if oxygen supply is limited, the body uses fermentation to keep going. An enzyme called lactate dehydrogenase (LDH) reduces pyruvate into lactate. This reaction uses NADH as an electron donor and regenerates NAD+. This regeneration is essential because it allows glycolysis to continue producing energy under anaerobic conditions.

Lactate does not simply build up indefinitely in the body. It is constantly being produced and removed. The concentration of blood lactate is usually low at rest. During intense exertion, it can rise to over 20mM. It can reach as high as 25mM immediately afterward. The body manages these levels through several mechanisms. These include monocarboxylate transporters and the oxidative capacity of different tissues. Once produced, lactate can be used in two main ways. Well-oxygenated cells in the heart, brain, and muscles can oxidize it back into pyruvate. Alternatively, the liver can convert it into glucose through a process called gluconeogenesis via the Cori cycle.

Industrial production of lactic acid relies on two main methods: fermentation and chemical synthesis. Most industrial lactic acid, between 70% and 90%, is produced through bacterial fermentation. Bacteria such as Lactobacillus casei and Lactococcus lactis consume carbohydrates like glucose, sucrose, or galactose. There are two types of bacteria used in this process. Homofermentative bacteria produce two moles of lactate from one mole of glucose. Heterofermentative species produce one mole of lactate, along with carbon dioxide and acetic acid or ethanol. Chemical synthesis is another option. This involves reacting acetaldehyde with hydrogen cyanide to create lactonitrile, which is then hydrolyzed.

History shows how our understanding of this acid has grown. The Swedish chemist Carl Wilhelm Scheele first isolated lactic acid in 1780 from sour milk. In 1808, Jöns Jacob Berzelius discovered that muscles also produce it during exertion. Later, in 1856, Louis Pasteur discovered the role of Lactobacillus in its synthesis. Johannes Wislicenus finally established its chemical structure in 1873. Even political history has touched this science. During the era of the Warsaw Pact, the Soviet Union faced shortages of other acids. They invested heavily in developing efficient Lactobacillus strains to produce lactic acid from molasses. This made lactic acid a much cheaper alternative to citric acid.

Today, the global demand for lactic acid is expanding rapidly. The industry sees an annual growth rate of 5% to 8%. This growth is driven by the need for biodegradable plastics and green solvents. Worldwide production exceeded 1.5 million tonnes by the early 2020s. This is a massive increase from the 275,000 tonnes produced in 2006. Major companies like NatureWorks LLC lead this production. One of their largest facilities is located in Blair, Nebraska. It has a production capacity of about 140,000 tonnes per year. This facility provides the materials needed for many biodegradable packaging and fiber applications.