MACRONUTRIENTS (CARBOHYDRATE)

CARBOHYDRATE

Carbohydrates are a group of nutrients important in the diet as a source of energy. They contain the elements carbon, hydrogen and oxygen and are produced in plants by the process of photosynthesis.

There are various different carbohydrates but they may be divided into three main groups according to the size of molecules.

MONOSACCHARIDES (SUGARS)

The monosaccharide sugars commonly found in food contain six carbon atoms and have the general formula C₆H₁₂O₆. 

The three most important members of this group are:

GLUCOSE

Glucose also known as dextrose found in fruits and vegetables. Large amount are found in fruits such as grapes and smaller quantities in vegetables such as young peas and carrots.

FRUCTOSE

Fructose also known as laevulose is chemically similar to glucose except the arrangement of molecules is slightly different. Fructose is found in many fruits and in honey.

GALACTOSE

Galactose also chemical similar to glucose. It does not exist as such in foods but is produced when lactose, a dissacharides is broken down during digestion.

DISACCHARIDES

These sugars have the general formula C₁₂H₂₂O₁₁. They are formed when two monosaccharaides  molecule combine with elimination of a water molecule.

           C₆H₁₂O₆  +  C₆H₁₂O₆  ------------> C₁₂H₂₂O₁₁ + H₂O

Three most important members of this group are:

SUCROSE

This is ordinary household sugar and is produced in plant by the condensation of glucose and fructose. Sucrose is found in sugarcane and sugar beet in relatively large amount and in some vegetables.

LACTOSE

This sugar is formed by the condensation of glucose and galactose. It is found only in milk where it is sole carbohydrate.

MALTOSE

A molecule of maltose is formed by the condensation of two glucose molecules.

POLYSACCHARIDES

Polysaccharides are the condensation polymers of monosaccharides and are made up of many molecules joined together with the elimination of one water molecule at each link. They have the general formula C₆H₁ₒO₅.

Following are the members of polysaccharides:

•        Starch
•       Glycogen 
•       Cellulose
•       Pectin
•       Gums, alginates and agar

STARCH

Starch is the major food reserve of plant. It is in fact a mixture of two polysaccharides.

Amylose: The amylose molecule consists of between 50 and 500 glucose units joined into a straight chain.

Amylopectin: This molecule consist of up to 100,000 glucose units joined in a branched chain structures.

The starch in many plants including wheat, rice, corn and potato consists of approximately 80% amylopectin and 20% amylose.

GLYCOGEN

This is the carbohydrate found only in animals.  It is the carbohydrate reserve in animals as the starch carbohydrate reserve in plants. Animals store glucose in muscles and liver, and required is converted into glucose which is then broken down to provide energy.

CELLULOSE

Cellulose is another polysaccharides consisting of long chains of glucose units. It acts as a structural material in plants, being found in cell-wall where it gives rigidity. It structure is similar to starch but glucose units are linked in different way. Human do not possess enzymes that are capable of breaking this type of linkage and therefore unable to use cellulose as food.

PECTIN

Pectin is a complex mixture of polysaccharides and found in many fruits and vegetables. Apples and peels of citrus fruits are particularly rich in pectin. Its main importance is a gelling agent, especially in jam making.

GUMS, ALIGANATES AND AGAR

Gums such as arabic and guar are produced by plants and are used in food manufacturing such as thickeners, stabilizers and gelling agents in a wide range of foods including ice cream, salad dressings, and fruits pie fillings. Agar is also used in the preparation of microbiological media