Polysaccharides are a class of biopolymers constituted with simple sugar monomers. It represents most of the structural and energy reserve carbohydrates found in nature.
Unlike protein, polysaccharides generally do not have definite molecular weight.
Many polysaccharides exist in the plant and animal kingdoms. However, only a few of these are known to be significant in mammalian nutrition, either as dietary constituents or as human cell metabolites.
The most common digestible polysaccharides in plant is starch, a polymer of glucose. It is composed of amylose and amylopectin. Starch is the energy compound stored predominantly in seeds and tubers. Glycogen is the animal counterpart of starch, but with shorter, more numerous branches.
The composition of starches also differs somewhat, but all types contain both amylase, a straight chain polymer of glucoses, and amylopectin, a branch chain polymer.
The average chain contains 20 to 25 glucose units with approximately 5 to 8 glucose molecules between branching points within the chain. On hydrolysis in the intestinal tract, starch yields dextrin and maltose and, eventually glucose.
Cellulose, the most abundant polysaccharide, is the structural component of plant tissues. It is the structural component of plant cell was, which consist of long chain of glucose residues.
Cellulose is not attacked by digestive enzymes of the human and although it provides bulk to the diet it does not contribute significantly to the nutrition of body cells.
It is fully permeable to water and solutes and therefore does not affect exchange of materials between the cells and the environment. Cellulose tends to be affected little by usual acid hydrolysis and requires the action of strong mineral acids.
Plants also contain indigestible hemicellulose, which are unrelated chemically to cellulose and are homopolysaccharides containing D-xylose. Homopolysaccharides are defined as polysaccharides formed from only one type of monosaccharide.
Pectin, present in fruit, is an indigestible heteropolymer and contains arabinose, galactose, and galacturonic acid. In general, heteropolysaccharides contain two or more different monosaccharides.
What does polysaccharide mean?
