lactose

lactose or milk sugar, white crystalline disaccharide (see carbohydrate ). It has the same empirical formula (C ₁₂ H ₂₂ O ₁₁ ) as sucrose (cane sugar) and maltose but differs from both in structure (see isomer ). It yields the simple sugars D-glucose and D-galactose on hydrolysis , which is catalyzed by lactase, an enzyme found in gastric juice. People who lack this enzyme after childhood cannot digest milk and are said to be lactose intolerant. Lactose is formed in the mammary glands of all lactating animals and is present in their milk. It is produced commercially as a byproduct of milk processing. When milk sours, the lactose in it is converted by bacteria to lactic acid. Lactose is less sweet-tasting than sucrose and is not found in plants.

lactose (milk sugar) A disaccharide sugar comprising glucose and galactose; it is the principal sugar in milk.

lactose (milk sugar) A sugar comprising one glucose molecule linked to a galactose molecule. Lactose is manufactured by the mammary gland and occurs only in milk. For example, cows' milk contains about 4.7% lactose. It is less sweet than sucrose (cane sugar).