Disaccharide known as double sugar, a saccharide compound, 十 composed of two monosaccharide molecules. Sucrose, lactose and maltose are common disaccharides. Sucrose is obtained from the dehydration condensation of one molecule of glucose and one molecule of fructose, or can be obtained from extracting from sugar cane or beet. Sucrose is the most common sugar in human life, and in the intestine it can be hydrolyzed into monosaccharides by the enzymatic of sucrose to be absorbed. Lactose is obtained from the dehydration condensation of one molecule of glucose and one molecule of galactose, and in the intestine it can be hydrolyzed into monosaccharides by the enzymatic of lactose to be absorbed. Lactose is only found in animal or human milk, milk contains 4% lactose, and human milk contains 5.7%. Lactose, owning the smallest sweetness in disaccharides, is particularly important for infant nutrition; it can also be used in high glucose energy liquid diet for athletes. Maltose obtained from the dehydration condensation of two molecules of glucose, is the product of grain germination. Malt, starch, glycogen can generate a small amount of maltose after hydrolyzed by amylase. Human saliva and pancreatic amylase hydrolyze starch can also generate maltose. Maltose is hydrolyzed into two glucose molecules by the enzymatic of maltose. The sweetness of maltose is about one-third of glucose, with the refreshing taste, and non-stimulation to gastric mucosa, it can be applied in athletes nutrition.
Free maltose and cellobiose do not exist in nature, the former is a partial hydrolyzate of starch, and the latter is a part of a cellulose hydrolysis product. Sucrose, lactose and maltose are good food, also used as industrial raw materials. Sucrose is usually used as raw materials to produce dextran in pharmacy. Lactose is used as tablets, powders, excipients or diluents.
Disaccharides are divided into two categories: reductive maltose-type and non-reductive trehalose-type. Maltose and lactose belongs to the former type. Maltose is the hydrolysate of starch, consisting of two molecules of glucose. Lactose presents in human and animal milk specifically, consisting of one molecule of glucose and one molecule of galactose. Sucrose, belonging to the latter one, is obtained from the condensation of one molecule of glucose and one molecule of fructose. There are specific enzymes breaking down the disaccharide in animals digestive tract, such as maltase, lactase and sucrase.
