Polysaccharides

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 glucose, fructose, galactose and mannose.

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

Three Main Polysaccharides

Three main polysaccharides related to the human nutrition include:

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

Chart 1. List of Polysaccharides and Food Examples

POLYSACCHARIDE	COMPOSITION	Kcal/g	FOOD SOURCE
DIGESTIBLE
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
NON-DIGESTIBLE (DIETARY FIBER)
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

Glycogen
Dietary fiber (cellulose, inulin, pectin, gums…)

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.