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Carbohydrates are organic compounds which consist of carbon, hydrogen and oxygen. Usually, hydrogen: oxygen atoms are in the ratio of 2:1. They are naturally occurring carbon compounds that also contain several hydroxyl groups. They are polyhydroxy aldehydes or ketones, or compounds that can be hydrolyzed to them. Carbonyl compounds of carbohydrates include ketones and aldehydes. Carbohydrates are the most abundant organic molecules in nature. They are also referred to as saccharides. Carbohydrates are technically hydrates of carbon. The empirical formula is Cn(H2O)n. Carbohydrates are also considered the most abundant biomolecules in terms of mass in our bodies.
Sources of Carbohydrates
Plants are the main source of carbohydrates. Some of the other sources are as follows:
1. Grain products
The leading source of carbohydrates includes grain products that we have in our diet. They mainly have a high concentration of starch which breaks down into sugar and acts as a source of carbohydrates in our body. Common grains include wheat, oats, rice and barley.
2. Starchy vegetables
Starchy vegetables include potatoes and corn. They have high levels of complex carbohydrates which are converted into sugar in our body.
3. Fruits
Almost all the fruits that we eat in our day-to-day life contain carbohydrates in the form of natural sugars.
4. Beverages
Among beverages, milk is one of the important sources of carbohydrates that is derived from animals.
5. Sweets and added sugars
Sweets are also a source of carbohydrates. Carbohydrates are added to many processed foods.
Classification of Carbohydrates
Carbohydrates are classified as Monosaccharides, Disaccharides and Polysaccharides.
1. Monosaccharides
Monosaccharides are the simplest form of sugar. They cannot be hydrolysed into smaller units. They are also called simple sugars. They possess a free aldehyde or Ketone and two or more hydroxyl groups. Monosaccharides having an aldehyde group as the carbonyl group are called aldoses. Monosaccharides having a Ketone group as the carbonyl group are called ketoses. Monosaccharides consist of a single polyhydroxy aldehyde or ketone unit. The most abundant monosaccharide in nature is the six-carbon sugar D-glucose, sometimes referred to as dextrose.
2. Disaccharides
Disaccharides are the form of carbohydrates that are composed of two monosaccharides. Disaccharides can be of two types- reducing disaccharides and non-reducing disaccharides.
3. Polysaccharides
Polysaccharides are the form of carbohydrates that contain more than ten monosaccharides bonded together by glycosidic bonds. They are also called glycans. They are a long chain of monosaccharides.
4. Aldoses
Monosaccharides having an aldehyde group as the carbonyl group are called aldoses. Their formula is Cn(H2O)n.
Structure of Aldoses
- They have an asymmetrical carbon centre which is why all aldoses usually exhibit stereoisomerism
- Depending on the chirality of the asymmetric carbon, they can exist in either L-form or D-form
- The determination of the D-form or L-form is done on the chirality of the asymmetric carbon farthest from the aldehyde end
- The simplest possible aldose is the triose glyceraldehyde
- It only contains three carbon atoms
- Usually, formaldehyde and glycolaldehyde are not considered carbohydrates, hence we cannot consider them as aldose
- Examples of aldoses are – glyceraldehyde, ribose, glucose, erythrose and galactose
Nomenclature of Aldoses
The number of carbons in the main chain helps us to differentiate different aldoses. The only aldotriose is glyceraldehyde.
Ketose
- A monosaccharide containing one ketone group per molecule is known as a ketose
- Dihydroxyacetone is the simplest form of ketone, containing only three carbon atoms and it is the only ketose with no optical activity
- Ketoses are generally classified on the basis of the number of carbons in the main chain
- Examples of ketoses are dihydroxyacetone, erythrulose, ribulose, xylulose, fructose, sorbose, nanose
Maltose
Maltose was discovered by French chemist Augustin-Pierre Dubrunfaut. The name maltose has been derived from the word ‘malt’ which means germinated grain, for use in brewing. Maltose is a disaccharide which is formed from the two units of the glucose molecule. Maltose is also known as malt sugar. It is prepared from starch by diastase. Maltose appears as white powder or crystals in nature.
Maltose Structure
Maltose is a disaccharide as it is made up of two glucose units. The formula of maltose is C12H22O11. Isomaltose is an isomer of maltose.
Properties of Maltose
- Maltose is a reducing sugar (like glucose)
- Maltose appears as white powder or crystal in nature
- The heat capacity of maltose is 298.15 K
- Maltose is soluble in water
- When sulphuric acid reacts with maltose, it forms carbon dioxide water and Sulphur dioxide
- Maltose forms ethanol and carbon dioxide when it undergoes hydrolysis
- It exhibits mutarotation in an aqueous solution
Uses of Maltose
- Maltose can be used as a carrying material for flavouring materials
- Maltose can be used in infant foods
- They are generally used for brewing
- Maltose is also used for the protection of the liver
- It is used for bakeries, soft drinks and sweets
Production of Maltose
They can be easily produced by the enzymatic hydrolysis of starch. Enzyme amylase is used as a catalyst in it.
Sucrose
One molecule of glucose and one molecule of fructose join together to form sucrose. Sucrose is a disaccharide that is composed of two monosaccharides.
Structure of Sucrose
- The molecular formula of sucrose is C12H22011
- It is a non-reducing disaccharide
Properties of Sucrose
- It is also known as table sugar or cane sugar
- It appears as a white crystalline solid in nature
- When sucrose undergoes a combustion reaction it forms carbon dioxide and water and when it reacts with chloric acid, it forms hydrochloric acid, carbon dioxide and water
Uses of Sucrose
- Sucrose is used in many pharmaceutical products
- It acts as a sweetening agent and acts as the most important component of many beverages
- It also acts as a food stabilizer, food preservative and antioxidant
Lactose
Lactose is a disaccharide which is composed of galactose and glucose. The name lactose has been derived from the lasting word ‘lac’ which means milk.
Structure of Lactose
It consists of one galactose and one glucose molecule and they are bound together by a glycosidic bond.
Uses of Lactose
- It is mainly used in pharmaceutical products
- It has some industrial applications also
- Lactose is also added to many products to carry and stabilize the aromas
Conclusion
Carbohydrates are considered the most abundant organic molecules in nature. They are also referred to as saccharides. Carbohydrates are technically hydrates of carbon. The empirical formula is Cn(H2O)n. Carbohydrates are also considered as the most abundant biomolecules in terms of mass in our body. Carbohydrates are classified as Monosaccharides, Disaccharides and Polysaccharides. Monosaccharides are the simplest form of sugar. They cannot be hydrolysed into smaller units. They are also called simple sugars. Disaccharides are the form of carbohydrates that are composed of two monosaccharides. Disaccharides can be of two types- reducing disaccharides and non reducing disaccharides. Polysaccharides are the form of carbohydrates that contain more than ten monosaccharides bonded together by glycosidic bonds. They are a long chain of monosaccharides.
Maltose is a disaccharide as it is made up of two glucose units. The formula of maltose is C12H22O11. They appear as white powder or crystal in nature. Maltose can be used as a carrying material for flavoring materials. They are also used for infant foods and for brewing.
Sucrose is a disaccharide which is made up of one molecule of glucose and one molecule of fructose. It is also known as table sugar and it appears as a white crystalline solid in nature. It can be used in many pharmaceutical products and as a food stabilizer.
Lactose is a disaccharide which is made up of one molecule of galactose and one molecule of glucose; it is mainly used in pharmaceutical products and in some industries.
Although sucrose, maltose and lactose are carbohydrates, they have a few differences. Lactose is a primary ingredient in the milk but it is not sweet whereas sucrose is well known for its sweetness, on the other hand maltose is also called malt sugar but it is not as sweet as sucrose.
