Disaccharids Sugars
The disaccharids sugars containing two hexose units-that are commonly encountered in foods include: sucrose (cane or beet sugar), maltose (malt sugar), and lactose (milk sugar). Disaccharides are hydrolyzed by specific enzymes in the digestive tract into monosaccharides or, commercially, by acid hydrolysis. Each of the three disaccharides has distinct characteristics that are of interest in human nutrition.
Sucrose-ordinary granulated, powdered, or brown sugar and molasses-is one of the sweetest forms of sugar. It is also found free in most fruits and vegetables. It s very soluble and on hydrolysis yields equal amounts of Zuctose and glucose, or invert sugar, as this mixture is commonly called.
Maltose, or malt sugar, does not occur free in nature it is manufactured from starch by enzyme or acid hyrolysis. It is less weet than sucrose and very soluble in water. Two molecules of glucose are formed by the hydrolysis of maltose. In the body it is an intermediate product in starch digestion.
Maltose, easily used by the body, is sometimes used in combination with dextrin, a polysaccharide, as an ingredient in home-prepared infant formulas, where it is desirable to have a soluble form of carbohydrate which does at readily ferment in the digestive tract.
Lactose, or milk sugar, is the only one of the common sugars not found in plants. It is not very soluble and is the .east sweet of the sugars, only about one-sixth as sweet as sucrose; this gives milk its blandness. It is formed only in the mammary glands of lactating mothers, animal or human. When lactose is hydrolyzed, a molecule of glucose and a molecule of galactose are formed. In the souring or fermenting of milk to make buttermilk or yogurt, some of the lactose can be converted to lactic acid. For this reason these products generally contain less lactose than milk.
A trisaccharide called raffinose, containing the ~hree hexoses-glucose, fructose, and galactose-is :bund along with sucrose in molasses. Maltotriose, an mtermediate product formed during the digestion of starch, contains three glucose units.
