disacchariden

Disacchariden, commonly called disaccharides, are a class of carbohydrates consisting of two monosaccharide units joined by a glycosidic bond. They are formed by a condensation reaction that releases a molecule of water and are typically soluble in water and have a characteristic sweet taste. The most familiar disaccharides in nature and the human diet are sucrose, lactose, and maltose.

Common examples include maltose, a glucose–glucose disaccharide linked by an α1→4 bond; lactose, a galactose–glucose disaccharide linked by a β1→4 bond; and sucrose, a glucose–fructose disaccharide linked by an α1→β2 bond between the anomeric carbons of both sugars. Because the glycosidic bond in sucrose involves the anomeric carbons of both monosaccharides, sucrose is non-reducing, whereas lactose and maltose are reducing sugars due to a free anomeric carbon.

In digestion, disaccharides are hydrolyzed by specific brush-border enzymes in the small intestine: sucrase breaks down sucrose, lactase cleaves lactose, and maltase (along with isomaltase) hydrolyzes maltose and related sugars. The resulting monosaccharides—glucose, galactose, and fructose—are absorbed into the bloodstream and transported to the liver.

Nutrition-wise, disaccharides provide quick energy and occur in various foods: sucrose in sugar cane and beet sugar; lactose in milk and dairy products; maltose in germinating grains and malt products. Individual tolerance varies, notably with lactase deficiency leading to lactose intolerance in some people.