Polysaccharides

The most common polysaccharides in nature

Carbohydrates of food interest can be divided into three categories: monosaccharides; oligosaccharides; polysaccharides. Monosaccharides include the simplest molecules, directly absorbable without the need for digestive process: the most common are glucose, fructose (present in fruit), galactose (which does not exist free in food, but is produced during the enzymatic digestion of lactose. in the intestine), mannose (which is bound to many proteins).

Oligosaccharides consist of a few units of monosaccharides: the most common are disaccharides (with two molecules of monosaccharides), including sucrose (formed by one molecule of glucose plus one of fructose), that is the common cooking sugar; maltose (formed by two glucose molecules), contained in cereals; lactose (made up of one molecule of galactose and one of glucose), whose only source is milk, human or animal. Polysaccharides are polymers produced by the aggregation of more than ten molecules of monosaccharides: the most important for nutrition are starch, glycogen, cellulose, all made up of long glucose molecules linked together in different ways. Starch is the most important reserve carbohydrate of the vegetable kingdom and is the main source of carbohydrates for human consumption (cereals, potatoes, legumes). Glycogen is a polysaccharide of the animal kingdom, contained in the liver and muscles as a storage form of carbohydrates: it has little nutritional importance. Cellulose constitutes the skeleton of vegetable fibers (woody and fibrous part of all plants): that contained in food is eliminated almost entirely with the faeces, to which it gives volume and consistency; only herbivorous animals have the enzymes to digest it.

Nutritional properties of polysaccharides

• ENERGY FUNCTION: they represent the main source of energy with rapid use and low cost.
• PLASTIC FUNCTION: they are constituents of nucleic acids, nucleotide coenzymes, glycolipids, glycoproteins, support and protective structures.
• REGULATORY FUNCTION of the metabolism as they determine a saving in the use of proteins for energy purposes.
• ANTICHETOGENIC FUNCTION: in case of glucose deficiency there is the formation of ketone bodies and metabolic acidosis.