A disaccharide is a carbohydrate formed by the condensation of two cyclic monosaccharides (pyranoses or furanoses):
The maltose can be obtained from the hydrolysis of starch from various cereals such as maize or barley. The malted barley is naturally produced during germination, production is accelerated during the manufacture of beer or malted barley syrup. Maltose is found in beer, cereals, pasta, potatoes and many processed products that have been sweetened.
Cellobiose is obtained by hydrolysis of cellulose. Recent research considers the conversion into fuel or glucose.
Lactose is a sugar found in milk (from $ 20$ to $ 80 \ frac {g} {L}$), of which it takes its name (etymologically milk sugar). The lactose is degraded in the digestive tract by an enzyme called ß-galactosidase by hydrolysis into glucose and galactose which are then absorbed separately. ß-galactosidase is present in children in the first years of life, but among the many adults enzyme production disappears and lactose remains in the digestive tract causing lactose intolerance. Undigested lactose is then metabolized by certain bacteria of the digestive system that begin to produce hydrogen in the presence of lactose. Symptoms of lactose intolerance are mainly bloating, painful stomach cramps and diarrhea.
Sucrose is ordinary sugar. It is obtained from sugar beet or sugar cane.