Oligosaccharides: Not So Simple, Not So Complex

Oligosaccharides are sugars, formed by the union of two to six monosaccharides, usually hexoses.

The prefix oligo is derived from Greek and means little. The most important oligosaccharides are disaccharides.

Sugars formed by the union of two monosaccharide units, such as sucrose, lactose and maltose. They are water soluble and have a sweet taste. For the formation of a disaccharide, reaction occurs between two monosaccharides, with release of a water molecule. It is common to use the term intermolecular dehydration for this type of reaction, where one water molecule results during the formation of one compound from two others.

Take the case of sucrose disaccharide, which is the most used sugar for the preparation of sweets, ice cream, to sweeten non-diet sodas and the "coffee". Its molecular formula is C12H22O11. This sugar is the result of the union of a fructose and a glucose. As seen in the previous table, both glucose and fructose have the molecular formula C6H12O6. As a water molecule is released to form sucrose, its molecular formula has two hydrogens and one less oxygen.

Disaccharide Constitution Biological paper Sources
Sucrose glucose fructose energetic sugar cane, sugar beet and rapadura
Lactose glucose-galactose energetic milk

Polysaccharides: The Most Complex

As the name suggests (poly is a Greek term meaning many), polysaccharides are macromolecular compounds (giant molecules) formed by the union of many (hundreds) monosaccharides. The three best known polysaccharides of living things are starch, glycogen and cellulose.

Unlike glucose, its polysaccharides have no sweet taste, nor are they water soluble.

Polysaccharide What is important to know


It is a polysaccharide of energetic reserve of the vegetables. Potatoes, rice and cassava are full of starch, stored by the vegetable and consumed at unfavorable times by the plant. The man knew how to take advantage of these characteristics and started to grow the starchy vegetables. The breads and cakes we eat are made from starchy flour. Remember that for starch to be used by our body, it has to be digested, which occurs first in the mouth and then in the intestine, with the addition of water and the participation of organic catalysts, ie substances that favor or accelerate the chemical reactions.


is an energy reserve polysaccharide of animals; therefore equivalent to vegetable starch. In our body, glycogen synthesis occurs in the liver from glucose molecules. Therefore, liver and chicken liver are foods rich in glycogen.


It is the structural role polysaccharide, that is, it participates in the plant cell wall. Few living things can digest it, including some microorganisms that inhabit the digestive tract of certain insects (termites) and that of ruminants (oxen, goats, sheep, deer, etc.).