Classification and Properties of Carbohydrates

Classification of Carbohydrates:

Carbohydrates have been classified into two groups:

  • Simple Carbohydrates
  • Complex Carbohydrates

Simple Carbohydrates:

Simple carbohydrates are sugars chemically referred to as monosaccharides and disaccharides. They are also known as single and double sugars respectively.

i. Monosaccharide: The simplest forms of carbohydrates are the monosaccharide. They include glucose, galactose, and fructose and they all have the same empiric formula, C6H12O6. Because of the six carbon atoms, they are all known as Hexoses. They differ in the arrangement of the groupings around the carbon atoms. They are distinctive in their physical properties such as solubility and sweetness. Glucose, galactose, and mannose possess an aldehyde grouping (CHO) and are known as Aldohexoses. Fructose possesses a ketone grouping (CO) and is known as Ketohexoses.

ii. Disaccharide: This group of carbohydrates is composed of 2 monosaccharides joined together, which split upon digestion. The most common are sucrose, lactose, and maltose. These three are called disaccharides or double sugars formed from the combination of two hexoses with the loss of one molecule of water. They are water-soluble, diffusible, and crystalizable and vary widely in their sweetness. They are broken into simple sugars by acid hydrolysis or by digestive enzymes.

Complex Carbohydrates:

Complex carbohydrates are sugars chemically referred to as oligosaccharides and polysaccharides.

i. Oligosaccharides: These are carbohydrates that comprise 3-10 monosaccharides. A good example is Honey, which is made up of plant nectar and contains sucrose and small amounts of starch that are harvested by the honeybee. The honeybee secretes sucrase which is also known as invertase and amylase, which together hydrolyze sucrose and starch into glucose and fructose. It helps to increase the sweetness of the product. Approximately 40% of the sugar in natural honey is free fructose.

ii. Polysaccharides: These carbohydrates are complex compounds composed of many molecules of simple sugars. They have a relatively high molecular weight that is known as amorphous. It is not sweet, is insoluble in water, and is digested with varying degrees of completeness. Starches, dextrins, glycogen, and several indigestible carbohydrates are of nutritional interest.