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Home » Reducing and Non Reducing Sugars with Examples

Reducing and Non Reducing Sugars with Examples

    In this reducing and non reducing sugars with examples post we have briefly explained about reducing sugar structure, non reducing sugar structure, Maltose, Sucrose, Lactose, Inversion of sucrose.

    Disaccharides are the most common. As is evident from the name, a disaccharide consists of two monosaccharide units (similar or dissimilar) held together by a glycosidic bond. They are crystalline, water-soluble and sweet to taste. The disaccharides are of two types.

    Reducing disaccharides: Reducing disaccharides with free aldehyde or keto group e.g. maltose, lactose. Non-reducing disaccharides: Non-reducing disaccharides with no free aldehyde or keto group e.g. sucrose, trehalose.

    Disaccharides

    Disaccharides Examples

    Reducing and Non Reducing Sugars with Examples

    Maltose

    Maltose is composed of two a-D-glucose units held together by α (1 -> 4) glycosidic bond. The free aldehyde group present on C1 of second glucose answers the reducing reactions, beside the osazone formations (sunflower-shaped). Maltose can be hydrolysed by dilute acid or the enzyme maltase to liberate two molecules of α-D-glucose.

    In isomaltose, the glucose units are held together by o (1 -> 6) glycosidic linkage. Cellobiose is another disaccharide, identical in structure with maltose, except that the former has β (1 -> 4) glycosidic linkage. Cellobiose is formed during the hydrolysis of cellulose.

    Sucrose

    Sucrose (cane sugar) is the sugar of commerce, mostly produced by sugar cane and sugar beets. Sucrose is made up of α-D-glucose and β-D-fructose. The two monosaccharides are held together by a glycosidic bond (α1 -> β2), between C1 of α-glucose and C2 of β-fructose.

    The reducing groups of glucose and fructose are involved in glycosidic bond, hence sucrose is a non-reducing sugar, and it cannot form osazones. Sucrose is the major carbohydrate produced in photosynthesis. It is transported into the storage organs of plants (such as roots, tubers and seeds). Sucrose is the most abundant among the naturally occurring sugars.

    It has distinct advantages over other sugars as a storage and transport form. This is due to the fact that in sucrose, both the functional groups (aldehyde and keto) are held together and protected from oxidative attacks.

    Sucrose is an important source of dietary carbohydrate. It is sweeter than most other common sugars (except fructose) namely glucose, lactose and maltose. Sucrose is employed as a sweetening agent in food industry.

    Lactose

    Lactose is more commonly known as milk sugar since it is the disaccharide found in milk. Lactose is composed of α-D-galactose and β-D-glucose held together by β (1 -> 4) glycosidic bond. The anomeric carbon of C1 glucose is free, hence lactose exhibits reducing properties and forms osazones (powder-puff or hedgehog shape).

    Lactose of milk is the most important carbohydrate in the nutrition of young mammals. It is hydrolysed by the intestinal enzyme lactase to glucose and galactose.

    Inversion of sucrose

    Sucrose, as such is dextrorotatory (±66.5⁰). But, when hydrolysed, sucrose becomes levorotatory (±28.2⁰). The process of change in optical rotation from dextrorotatory (+) to levorotatory (-) is referred to as inversion. The hydrolysed mixture of sucrose, containing glucose and fructose, is known as invert sugar. The process of inversion is explained below. Hydrolysis of sucrose by the enzyme sucrase (invertasd or dilute acid liberates one molecule each of glucose and fructose.

    It is postulated that sucrose (dextro) is first split into α-D-glucopyranose (+52.5⁰) and β-D-fructofuranose, both being dextrorotatory. However, β-D-fructofuranose is less stable and immediately gets converted to β-D-fructopyranose which is strongly levorotatory (-92″). The overall effect is that dextro sucrose (+66.5⁰) on inversion is converted to levo form (-28.2⁰).

    Further Readings

    Reference

    1. https://umaine.edu/carbohydrates/carbohydrate-chemistry/oligosaccharides/
    2. http://www.citycollegiate.com/biochemistry2.htm