Lactose

Milk has a sweet taste.

This taste comes from a sugar. This sugar is found in milk from many animals. It is made of two smaller sugars joined together.

Baby animals drink milk to grow. Their bodies use a special tool to break the sugar down. This tool turns the sugar into food.

Some people cannot break this sugar down. This can make their tummies feel bad.

This sugar is a white solid. It can also be used to make medicine. It is a very useful part of milk.

Milk has a sweet taste. This taste comes from a sugar called lactose.

Lactose is a white solid that dissolves in water. It is made of two smaller sugars. These are called glucose and galactose. Lactose makes up about 2% to 8% of milk. Many mammals have it in their milk. For example, cow milk has about 4.8% lactose. Rhesus macaque monkeys have 8% lactose. Some animals, like bears, have no lactose in their milk at all.

Baby animals drink milk to grow. Their bodies use a special tool to break the sugar down. This tool is an enzyme called lactase. The lactase splits the lactose into glucose and galactose. Then, the body can use those sugars for power.

In many animals, the body stops making lactase as they grow up. This happens when they stop drinking milk. Some people can still make lactase as adults. This is common in parts of Europe and Africa. Other people cannot break the sugar down. This is called lactose intolerance. It can cause tummy pain or bloating.

Lactose is also very useful. It is used to make baby formula. It can even be used to make medicine. Some beers use it to add sweetness.

Lactose is a special kind of sugar found in milk. It is a white solid that dissolves easily in water. This sugar has a mildly sweet taste. Scientists call it a disaccharide. This means it is made of two smaller sugars joined together. Those two sugars are called glucose and galactose.

Lactose is very important for many living things. It provides energy to baby animals as they grow. It is also used by people in many different ways today.

Inside the body, lactose works through a specific way it works. When a mammal drinks milk, the sugar enters the digestive system. The small intestine has tiny parts called villi. These villi release a special tool called the enzyme lactase. This enzyme performs a job by cleaving the lactose molecule. It splits the big sugar into its two parts, glucose and galactose. Once they are split, the body can absorb them for energy.

People have been studying this sugar for a long time. In 1633, a doctor named Fabrizio Bartoletti published a way to find it. He called it the "manna of whey." Later, in 1780, Carl Wilhelm Scheele identified it as a sugar. In 1812, Heinrich Vogel found that lactose could turn into glucose. Louis Pasteur helped more in 1856 when he found galactose. Finally, Jean Baptiste André Dumas gave it the name lactose in 1843.

Lactose appears in different amounts in different animals. For example, cow milk has a concentration of about 4.8%. Rhesus macaque monkeys have even more at 8%. However, some animals like bears produce milk with no lactose at all. In the food industry, lactose is often made from whey. Whey is the liquid left over when making cheese. This liquid can be evaporated and cooled to create pure lactose crystals.

We see lactose used in many items in our daily lives. It is a key part of infant formula to match human milk. Some people make stout beer with lactose to add sweetness. It is also used in the pharmaceutical industry. It helps hold medicines together in tablets or capsules. While some people cannot digest it well, it is very useful. It even helps the body absorb minerals like calcium and magnesium.

Lactose is a disaccharide, which is a type of sugar made of two smaller sugar units. Its chemical formula is C12H22O11. It is a white, water-soluble solid that tastes mildly sweet. The name comes from the Latin word for milk, *lac*, plus the suffix *-ose* used for sugars. This substance is found in the milk of many different mammal species. It serves as a vital energy source for nursing infants.

Lactose is composed of two specific sugars: galactose and glucose. These two units are joined by a β-1→4 glycosidic linkage. This means the galactose and glucose are connected at specific points in their molecular structures. Because of how they are joined, lactose can exist in different forms. It can be α-lactose or β-lactose depending on the shape of the glucose ring. The galactose part stays in the β-pyranose form. This complex structure determines how the sugar behaves in chemical reactions.

To use this sugar for energy, the body must break it down. This process is called hydrolysis. In the digestive system, the intestinal villi secrete an enzyme called lactase, or β-D-galactosidase. This enzyme acts like a pair of molecular scissors. It cleaves the lactose molecule into its two subunits, glucose and galactose. Once separated, these simple sugars are small enough to be absorbed into the bloodstream. If the enzyme is not present, the lactose remains whole and moves through the gut. This can provide food for gas-producing bacteria, causing bloating or diarrhea.

Lactose concentrations vary significantly across the animal kingdom. For example, bovine milk, or cow milk, contains about 4.8% lactose by mass. Rhesus macaque monkeys have a much higher concentration at 8%. However, some mammals, such as bears, produce milk that contains no lactose at all. In the dairy industry, lactose is often extracted from whey. Whey is the liquid left after milk is curdled to make cheese. Scientists can purify lactose from whey permeate by evaporating it to 60–65% solids and then crystallizing it as it cools.

Humans have studied this sugar for hundreds of years. In 1633, physician Fabrizio Bartoletti published a method to isolate a substance he called the "manna of whey." In 1780, Carl Wilhelm Scheele identified it as a sugar. Later, in 1812, Heinrich Vogel discovered that glucose is produced when lactose is hydrolyzed. In 1843, the chemist Jean Baptiste André Dumas gave it the name "lactose." By 1856, Louis Pasteur crystallized galactose, the other part of the sugar. Finally, Emil Fischer established the exact molecular configurations of the component sugars by 1894.

Lactose has many specific biological and chemical properties. Its sweetness is relatively low, measuring only 0.2 to 0.4 compared to sucrose. When fully digested, it provides 4 kcal/g of energy. However, if it is not fully digested, its caloric value can range from 2 to 4 kcal/g. It also has a glycemic index between 46 and 65. This is lower than the index for glucose, which is 100 to 138. Interestingly, lactose has low cariogenicity, meaning it is less likely to cause tooth decay. This is because oral bacteria do not ferment it rapidly.

Today, lactose is used in many different industries. In the food industry, it is used in infant formula to match the composition of human milk. It is also used to sweeten certain types of beer, like milk stouts. In the pharmaceutical industry, lactose is a common ingredient in tablets and capsules. It acts as a carrier or stabilizer for various drugs, such as atorvastatin. Because it is a stable solid, it helps hold medicine together. It can even be used to help the body absorb minerals like calcium and magnesium.