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What Are Oligosaccharides?
Oligosaccharides are carbohydrates that contain two or more than two monosaccharides (2-10 units of monosaccharides). Oligosaccharides may contain any sugar monomer, but fructooligosaccharides (e.g., oligofructose) and galactooligosaccharides are mostly researched. Some oligosaccharides get absorbed in the small intestine after getting hydrolsed, for example, maltotriose.
Classification of Oligosaccharides
The classification depends on the number of sugar units they are made up of. These include the following:
Trisaccharides: These types of oligosaccharides are made up of three monosaccharides linked together. Raffinose is an example of a trisaccharide which is composed of glucose, galactose and fructose.
Tetrasaccharides: These are composed of four sugar units. Sesamose, which is made up of four monosaccharides — 2 galactose units, one unit of fructose and one glucose unit.
Pentasaccharides: They are composed of five monosaccharides. Examples include verbascose, which is composed of three units of galactose, one unit of fructose and one unit of glucose.
Hexasaccharides: These are made up of six sugar units.
Similarly, Heptasaccharides have seven sugar units, octasaccharides have eight monosaccharides, etc.
Examples of Oligosaccharides
Raffinose family of oligosaccharides
Raffinose, a trisaccharide having formula C18H32O16 is formed with three sugar units – fructose, glucose, and galactose. It produces D-galactose and sucrose when it gets hydrolysed with α-galactosidase enzyme. It is found in legumes, beetroots, cabbage, cottonseed, broccoli, etc.
Fructooligosaccharides
Fructooligosaccharides are plant-derived oligosaccharides. They are also termed as oligofructans and are considered to be storage saccharides. These are short chains of fructose residues which are common in plants. Examples include Agave tequilana, Helianthus tuberosus, banana, onion, wheat, barley, etc. They are commercially used as food additives to enhance colour and texture, and also as artificial sweeteners.
Galactooligosaccharides
Galactooligosaccharides are made up of galactose molecules. Example: Human milk oligosaccharides (HMOs). They are present in breast milk. They are derived from lactose. 2′-fucosyllactose, i.e., a trisaccharide composed of fucose, galactose, and glucose accounts for 30% of all HMOs.
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