DISACCHARIDES

DEFINITION
A disaccharides is the carbohydrate formed when two monosaccharides undergo a condensation reaction which involves the elimination of a small molecule, such as water, from the functional groups only. Like monosaccharides, disaccharides form an aqueous solution when dissolved in water. Three common examples are sucrose, lactose and maltose.
'Disaccharide' is one of the four chemical groupings of carbohydrates (monosaccharides, disaccharides, and polysaccharides)


 CONTENTS
There are two different types of disaccharides: reducing disaccharides, in which one monosaccharide, the reducing sugar, still has a free hemiacetal unit; and non-reducing disaccharides, in which the components bond through an acetal linkage between their anomeric centers and neither monosaccharide has a free hemiacetal unit. Maltose is examples of reducing disaccharides. Sucrose is examples of non-reducing disaccharides.


CLASSIFICATION
There are two different types of disaccharides: reducing disaccharides, in which one monosaccharide, the reducing sugar, still has a free hemiacetal unit; and non-reducing disaccharides, in which the components bond through an acetal linkage between their anomeric centers and neither monosaccharide has a free hemiacetal unit. Maltose are examples of reducing disaccharides. Sucrose and are examples of non-reducing disaccharides.


FORMATION
Disaccharides are formed when two monosaccharides are joined together and a molecule of water is removed, a process known as dehydration reaction. For example; milk sugar (lactose) is made from glucose and galactose whereas the sugar from sugar cane and sugar beets (sucrose) is made from glusose and fructose. Maltose, another notable disaccharide, is made up of two glucose molecules.The two monosaccharides are bonded via a dehydration reaction (also called a condensation reaction or dehydration synthesis) that leads to the loss of a molecule of water and formation of a glycosidic bond.


PROPERTIES
The glycosidic bond can be formed between any hydroxyl group on the component monosaccharide. So, even if both component sugars are the same (e.g., glucose), different bond combinations (regiochemistry) and stereochemistry (alpha- or beta-) result in disaccharides that are different chemical and physical properties.

Depending on the monosaccharides constituents, disaccharides are sometimes crystalline, sometimes water-soluble, and sometimes sweet-tasting and sticky-feeling.

MALTOSE

Maltose also known as maltobiose or malt sugar, is a disaccharide formed from two units of glucose joined with an α(1→4) bond, formed from a condensation reaction. The isomer isomaltose has two glucose molecules linked through an α(1→6) bond. Maltose is the second member of an important biochemical series of glucose chains. Maltose is the disaccharide produced when amylase breaks down starch. It is found in germinating seeds such as barley as they break down their starch stores to use for food. It is also produced when glucose is caramelized.

Maltose can be broken down into two glucose molecules by hydrolysis. In living organisms, the enzyme maltase can achieve this very rapidly. In the laboratory, heating with a strong acid for several minutes will produce the same result. Isomaltose is broken by isomaltase

SUCROSE

Sucrose is the organic compound commonly known as table sugar and sometimes called saccharos. A white, odorless, crystalline powder with a sweet taste, it is best known for its role in food. The molecule is a disaccharide composed of the monosaccharides glucose and fructose with the molecular formula C₁₂H₂₂O₁₁. The word was formed in the mid-19th century from Latin sucrum = "sugar" and the chemical suffix -ose. The abbreviated term Suc is often used for sucrose in the literature.

LACTOSE

Lactose is a disaccharide sugar derived from galactose and glucose that is found in milk. Lactose makes up around 2~8% of milk (by weight), although the amount varies among species and individuals. It is extracted from sweet or sour whey. The name comes from lac or lactis, the Latin word for milk, plus the -ose ending used to name sugars. It has a formula of C₁₂H₂₂O₁₁.