DISACCHARIDES

• They are oligosaccharides composed of two monosaccharide residues .
• Three common disaccharides are   sucrose (glucose + fructose) = cane suger maltose (glucose + glucose) = malt sugar lactose (glucose + galactose) = milk sugar
• Common formula is C_n(H₂O)_n-1.

SUCROSE

• Commercial or Table sugar.
• Obtained from stems of Sugarcane (Saccharum officinarum) and roots of Beet sugar (Beta vulgaris).
• Sucrose is a non-reducing sugar.
• Sweetness index of sucrose is 100.
• Formed of two molecules each of glucose and fructose.
• It has neither aldehyde group nor keto group.

MALTOSE

• Malt Sugar
• It is a disaccharide formed of two molecules of glucose which are connected to each other through the a -1, 4 D-glycosidic linkage.
• It is present in Barley.
• Maltose is formed during hydrolysis of starch.
• It is found in germinating cereals.
• The sugar is present in malt, and is therefore, also called malt sugar.
• Sweetness index is 30.
• Maltose is a reducing surgar.

LACTOSE

• Milk Sugar.
• It is a disaccharide sugar present in milk upto the extent of 5%.
• Lactose is formed of D-galactose and D-glucose, both in pyranose state, through the b-1, 4 glycocydic bond.
• The monosaccharide galactose is also synthesised from glucose inside the mammary glands.
• Sweetness index of lactose is 16.
• Like maltose, lactose is a reducing sugar.
• Souring of milk occurs when bacteria convert lactose into lactic acid.
• Present only in mammals.

TREHALOSE

• It is a disaccharide sugar made of two glucose residues which was originally obtained from cocoon of Trehela (weevil Larinus species) as sweetening agent.
• Trehalose is found in haemolymph of some insects and fungi including yeast.