Lactose is a disaccharide consisting of galactose and glucose, linked by a β-L-4 glycosidic bond. Its systematic name is β-0-D-galactopyranosyl-(1–4)- α-D-glucopyranose (α-lactose) or β-0-D-galactopyranosyl-(1–4)-β-D-glucopyranose (β-lactose).
Lactose is a disaccharide, composed of two molecules of monosaccharides; glucose, and galactose. Lactose is readily fermented by the lactic acid fermenting bacteria producing lactic acid and has significance in milk and milk products.
Lactose in solid form can either be in a crystalline state or in an amorphous state. Crystalline lactose can exist in a number of distinct forms. Most well-known are α-lactose monohydrate and β-lactose. Β form is more soluble than the α form in water.
Neither α-lactose hydrate nor β-lactose is hygroscopic. However, anhydrous α-lactose is strongly hygroscopic and can absorb moisture from the air, forming the hydrate that occupies more volume than the anhydrous form.
Lactose is not digested until it reaches the small intestine, where the hydrolytic enzyme lactase is located. Lactase (β-galactosidase), which is located in brush border epithelial cells of the small intestine, catalyzes the hydrolysis of lactose into its constituent monosaccharides. Only monosaccharides among the carbohydrates are absorbed from the intestines.
Characteristics of lactose
