Disaccharide

A carbohydrate composed of two monosaccharide units joined by a glycosidic bond. Its properties depend on the sugars, linkage position, and anomeric configuration.

Monosaccharide: A simple sugar consisting of a single carbohydrate unit that cannot be hydrolyzed into smaller carbohydrates. Disaccharides form when two of these units are joined.
Sucrose: A nonreducing disaccharide of glucose and fructose joined through both anomeric carbons. Its two anomeric carbons are tied up in the bond, making sucrose nonreducing.
Condensation reaction: A reaction in which two molecules join while releasing a small molecule, often water. A condensation reaction can form the bond between two monosaccharides.
Lactose intolerance: A condition in which insufficient lactase activity causes symptoms after lactose consumption. It links a specific disaccharide to a common digestive difficulty.
Polysaccharide: A carbohydrate composed of many monosaccharide units linked in chains or branched structures. It contrasts with disaccharides in chain length and structural complexity.
Glycosidic bond: A covalent bond linking a sugar’s anomeric carbon to another group, including another sugar. This bond connects the two monosaccharides in a disaccharide.
Lactose: A reducing disaccharide of galactose and glucose joined by a β(1→4) linkage. Its free glucose anomeric carbon allows reducing behavior.
Reducing sugar: A sugar capable of reducing certain reagents because it has a free anomeric carbon or can form one. Whether a disaccharide has a free anomeric carbon determines if it is reducing.
Lactose-free milk: Milk in which lactose has been hydrolyzed or removed to reduce its lactose content. Lactase treatment converts lactose into more readily absorbed sugars.
Oligosaccharide: A carbohydrate composed of a small number of monosaccharide units, typically more than two. Disaccharides sit at the smallest end of the oligosaccharide range.

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