: a disaccharide sugar C12H22O11 that is present in milk, yields glucose and galactose upon hydrolysis, yields especially lactic acid upon fermentation, and is used chiefly in foods, medicines, and culture media (as for the manufacture of penicillin)—called also milk sugar
Slightly sweet sugar (disaccharide) composed of two monosaccharides, glucose and galactose, linked together. Lactose-intolerant adults, and more rarely infants, cannot digest lactose because they lack the enzyme (lactase) that splits it into simpler sugars and suffer diarrhea and bloating when they eat foods containing it. Lactose, which makes up 2–8% of the milk of mammals, is the only common sugar of animal origin. Commercial lactose is obtained from whey, a liquid by-product of cheese. It is used in foods, in pharmaceuticals, and in nutrient broths used to produce penicillin, yeast, and riboflavin, and other products.