What are the four types of disaccharides?

November 25, 2025 •

2 min read

Did you know that sucrose is just one of many different disaccharides found in nature? The four types of disaccharides are double sugars formed from two linked monosaccharides, with their distinct properties defined by their specific building blocks and bonding.

Quick Summary

Explains the four major types of disaccharides: sucrose, lactose, maltose, and cellobiose. Covers their unique monosaccharide composition, glycosidic linkages, and functions.

Key Points

Sucrose is Non-Reducing: As table sugar, sucrose is composed of glucose and fructose linked by an α-1,β-2 glycosidic bond, which involves both anomeric carbons, making it non-reducing.
Lactose is Milk Sugar: Lactose is a reducing disaccharide made of galactose and glucose, linked by a β-1,4-glycosidic bond, and is the primary sugar in milk.
Maltose is Malt Sugar: Maltose is a reducing disaccharide consisting of two glucose units connected by an α-1,4-glycosidic bond, found in grains.
Cellobiose comes from Cellulose: Cellobiose consists of two glucose units with a β-1,4-glycosidic bond and is the product of cellulose degradation, indigestible by humans.
Linkage Type is Critical: The specific type of glycosidic linkage, whether alpha or beta, determines the overall structure, properties, and digestibility of each disaccharide.

Disaccharides, also known as 'double sugars,' are carbohydrates formed by the joining of two monosaccharide units through a glycosidic linkage. This bond is created during a dehydration synthesis reaction. The specific monosaccharides and the type of glycosidic bond determine the unique characteristics, functions, and sources of each disaccharide. While numerous disaccharides exist, the four most commonly discussed types are sucrose, lactose, maltose, and cellobiose.

Sucrose

Common table sugar, sucrose, is composed of glucose and fructose linked by an α-1,β-2 glycosidic bond. This bond involves both anomeric carbons, classifying sucrose as a non-reducing sugar. It is naturally present in plants like sugar cane and sugar beets and serves as an energy transport molecule.

Lactose

Lactose, or 'milk sugar,' is a reducing disaccharide found in milk, essential for infant nutrition. It consists of galactose and glucose joined by a β-1,4-glycosidic bond. The free hemiacetal group on glucose makes it a reducing sugar. Lactose intolerance results from the inability to digest this β-1,4 linkage due to insufficient lactase enzyme.

Maltose

Maltose, 'malt sugar,' is a reducing disaccharide produced during starch breakdown and found in grains. It is composed of two glucose molecules linked by an α-1,4-glycosidic bond. This alpha linkage is easily broken down by maltase during digestion.

Cellobiose

Cellobiose is a reducing disaccharide resulting from cellulose breakdown, the main structural component of plants. It is made of two glucose units connected by a β-1,4-glycosidic bond. Unlike maltose, this beta linkage makes cellobiose indigestible by human enzymes. It is primarily used in chemical analysis.

The Function and Significance of Disaccharides

The four types of disaccharides serve diverse biological roles:

Energy: Sucrose and maltose provide readily available energy.
Nutrient: Lactose is a crucial energy source for young mammals.
Digestion Intermediate: Maltose is an intermediate step in starch digestion.
Structural Indicator: Cellobiose indicates cellulose degradation.

A Comparison of the Four Types of Disaccharides


Feature	Sucrose	Lactose	Maltose	Cellobiose
Monosaccharide Units	Glucose + Fructose	Galactose + Glucose	Glucose + Glucose	Glucose + Glucose
Glycosidic Linkage	α-1,β-2	β-1,4	α-1,4	β-1,4
Reducing/Non-Reducing	Non-Reducing	Reducing	Reducing	Reducing
Common Source	Table sugar, fruits	Milk	Malted grains, cereals	Cellulose hydrolysis
Digestible by Humans?	Yes	Yes (with lactase)	Yes	No

Conclusion

The exploration of what are the four types of disaccharides—sucrose, lactose, maltose, and cellobiose—reveals the structural and functional diversity possible from combining simple sugar units. The specific monosaccharides and their glycosidic bonds dictate the unique properties of each disaccharide, impacting everything from their taste to how they are metabolized. This foundational knowledge is critical in various scientific disciplines, including nutrition and material science. Further details on these structures can be found at Chemistry LibreTexts.

Frequently Asked Questions

A reducing disaccharide, like lactose or maltose, has a free hemiacetal unit that can donate electrons, causing it to react with certain chemical reagents. A non-reducing disaccharide, like sucrose, lacks this free unit because both anomeric carbons are involved in the glycosidic bond, preventing it from acting as a reducing agent.

Sucrose is made of glucose and fructose. Lactose is composed of galactose and glucose. Maltose consists of two glucose molecules.

Disaccharides are formed when two monosaccharides join together via a dehydration synthesis (or condensation) reaction. During this process, a hydroxyl group from one monosaccharide and a hydrogen from another are removed, forming a water molecule and a glycosidic bond between the two sugars.

Disaccharides primarily serve as an energy source, which is released when they are broken down into monosaccharides during digestion. They also act as transport sugars in plants, storage forms of energy, and are used as sweeteners in food products.

Lactose intolerance is a digestive disorder caused by the body's inability to produce sufficient amounts of the lactase enzyme. Without lactase, lactose cannot be properly broken down into glucose and galactose, leading to digestive issues when consuming dairy products.

Cellobiose is not typically found free in nature but is produced during the breakdown (hydrolysis) of cellulose, the tough structural component of plant cell walls.

No, not all disaccharides are sweet. While sucrose is very sweet and maltose has a noticeable sweetness, lactose is only slightly sweet. Cellobiose also has a mild, less palatable sweetness.