A disaccharide is a sugar (a carbohydrate) composed of two monosaccharides, such as glucose and fructose that make up the disaccharide sucrose. It is formed when two sugars are joined together and a molecule of water is removed. Due to this, disaccharides cannot hydrolyse, meaning their molecules are unable to be broken down through a reaction with water. For example, milk sugar (lactose) is made from glucose and galactose whereas cane sugar (sucrose) is made from glucose and fructose.
Common disaccharides
| Disaccharide | Unit 1 | Unit 2 | Bond | Notes |
| Sucrose (table sugar, cane sugar, saccharose, or beet sugar) | glucose | fructose | α(1→2) | Sucrose is found naturally in many food plants. |
| Lactose (milk sugar) | galactose | glucose | β(1→4) | Lactose is found in milk products. |
| Maltose | glucose | glucose | α(1→4) | Produced during the malting of barley |
| Trehalose | glucose | glucose | α(1→1)α | Present in fungi and insects. Successfully produced at an industrial scale by enzymatic treatment of starch for use as a food ingredient. |
| Cellobiose | glucose | glucose | β(1→4) | - |
Maltose and cellobiose are hydrolysis products of the polysaccharides, starch and cellulose, respectively. Some common Disaccharides are: Maltose, Lactose and Sucrose.