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Polysaccharides Definition and Structure

Polysaccharides [Greek poly = many; sacchar = sugar] are complex carbohydrates, composed of 10 to up to several thousand monosaccharides arranged in chains. The most common monosaccharides that appear as parts of polysaccharides are glucosefructose, galactose and mannose.

Polysaccharides examples and structure image

Picture 1. A polysaccharide example:
starch, made of glucose molecules

Three Main Polysaccharides

Three main polysaccharides related to the human nutrition include:

  1. Starch ─ an energy source obtained from plants
  2. Cellulose ─ a structural polysaccharide in plants; when consumed, it acts as a dietary fiber
  3. Glycogen ─ a storage form of glucose in the human liver and muscles

Chart 1. List of Polysaccharides and Food Examples

Starch Glucose 4.2 Cereal grains (wheat, oats, barley, corn, rice…) and their products (bread, pasta, pastries, cookies), potatoes, tapioca, yam, legumes
Dextrin (starch gum) Glucose 3.8 An artificially produced food additive
Glycogen Glucose 4 Shellfish, animal liver
Cellulose Glucose 0 Whole grains, green leafy vegetables, beans, peas, lentils
Hemicellulose Arabinose + xylose 0 Cereals bran
Polydextrose Glucose 1.2 A food additive
Inulin Fructose + glucose 1-2 Wheat, onions, chicory root, leeks; a food additive
Beta-glucan Glucose ~2 Barley, whole oats, supplements
Pectin Various monosaccharides 3.3 Fruits, carrots, sweet potatoes; a food additive
Psyllium husk mucilage Various monosaccharides Psyllium seed husk
Galactomannans or gums: beta-mannan, carob, fenugreek, guar and tara gum Galactose + mannose 1-4 A food additive derived from beans and seeds
Glucomannan or konjac gum Glucose + mannose 0 A food additive extracted from konjac plant
Other natural gums: gum acacia (arabic), karaya, tragacanth Various monosaccharides 1.7 Food additives
Artificially produced gums: arabinoxylan (soluble), gellan, xanthan Various monosaccharides <2 Food additives
Seaweed polysaccharides: agar-agar, alginate, carrageenan Galactose Food additives derived from marine algae
Chitin and chitosan Glucosamin Dietary supplements, derived from shells of crustaceans

Polysaccharides Types, Digestion, Function and Benefits

Digestible polysaccharides, such as starch, are digested (broken down) in the mouth and small intestine in several steps that eventually yield glucose, which is absorbed. They are a source of energy; they provide about 4 Calories (kilocalories) per gram. They also provide carbon atoms for the synthesis of fats, proteins and other substances in your body.

Non-digestible polysaccharides or dietary fiber, such as cellulose, promote the passage of food through the gut and thus help maintain bowel regularity. Some non-digestible polysaccharides, such as inulin, may also promote the growth of beneficial intestinal bacteria.

None of the polysaccharides are essential nutrients; you do not need to consume them in order to be healthy.

Non-Starch Polysaccharides

Plant and Animal Sources of Polysaccharides

Plant foods are by far the commonest source of polysaccharides:

  • Starch is in cereal grains (wheat, oats, rye, barley, buckwheat, rice, etc.), potatoes and legumes (beans, peas, lentils).
  • Fiber is mainly in whole grains (whole-grain bread, brown rice, etc.), legumes, vegetables and fruits.

Animal foods are a poor source of polysaccharides:

  • A small amount of glycogen is in shellfish and animal liver.
  • An indigestible fiber chitin and its derivative chitosan are in shells of crustaceans (crabs, shrimps).

Polysaccharides as Food Additives

Naturally-occurring or artificially produced polysaccharides added to commercial foods as thickeners or fibers include various types of starches, dextrin, polydextrose, inulin and gums.

Storage vs Structural Polysaccharides

Storage polysaccharides are a storage form of energy, for example cellulose in plants and glycogen in animals and humans.

Structural polysaccharides give structure to plants; examples include cellulose in plants and chitin in the shells of crustaceans.

Related Nutrients

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