Non-Starch Polysaccharides

Non-starch polysaccharides (NSPs) is the name of a category of chemicals found naturally in plants.

Non-starch polysaccharides (NSPs) are also known collectively as:

• dietary fibre (British English spelling)
• dietary fiber (American English spelling), and
• roughage (older term in wide colloquial use).

In terms of both chemistry and diet and nutrition, non-starch polysaccharides are a type of carbohydrate.

When to say "non-starch polysaccharides" and when to say "dietary fibre" (or equivalent):

Although these expressions refer to the same chemicals, some textbooks use them inter-changeably.

In general, 'dietary fibre' is used when describing and discussing NSPs in the diet, e.g. their functions and benefits and how they are processed by the human digestive system. 'Non-starch polysaccharides' are usually referred to when describing and explaining the chemistry, and therefore also the chemical reactions of NSPs. Obviously these areas are closely related because the digestive process includes chemical digestion e.g. due to the actions of acids, enzymes and bile.

• The page about dietary fibre mentions types of dietary fibre, the functions and benefits of dietary fibre and sources of dietary fibre with examples of high fibre foods and low fibre foods.
• This page about non-starch polysaccharides explains the general chemical structure of NSPs as compared with e.g. monosaccharides and disaccharides. It also lists examples of specific NSPs.

Polysaccharides compared with other carbohydrates:

As explained on the page about types of sugar (monosaccharides and disaccharides), there are 4 general categories of carbohydrates which can be listed in increasing size and complexity as:

1. Monosaccharides soluble in water, therefore a type of sugar Simple 'unit' sugar molecules. 2. Disaccharides soluble in water, therefore a type of sugar Consist of molecules whose form is that of two monosaccharide molecules joined together. 3. Oligosaccharides often only partially digestible by humans Consist molecules whose form is that of 3-10 monosaccharide molecules joined together. 4. Polysaccharides insoluble in cold water tasteless either partially digestible or indigestible to humans Consist molecules whose form is that of many monosaccharide molecules joined together.

The table above helps to explain the "polysaccharide" part of the term non-starch polysaccharides.

That is:

Although the general properties of polysaccharides include insolubility in cold water, no taste, and indigestible to humans, polysaccharides do play an important role in the human digestive system - as described on the page about dietary fibre.

Main types of polysaccharides:

There are many types of polysaccharides found in plant materials commonly included in human diets.

Important examples include:

1. Starch Chemically, consists of long chains of glucose (a monosaccharide, see above) molecules Formed by plants during photosynthesis Present in many plant-based food sources, such as root vegetables. e.g. potatoes, cereals e.g. and pulses. 2. Dextrin Formed when starchy foods (i.e. foods that contain starch, such as bread or potatoes) are baked or toasted. Dextrin is formed as part of the dry 'crust' Dextrin is more soluble than starch 3. Cellulose Chemically, consists of long chains of glucose (a monosaccharide - see above) molecules Forms the structure of some plants Indigestible by humans but digestible by some other animals. Valuable in human diet as source of dietary fibre - which used to be known as "roughage" 4. Pectin Present in the roots and/or fruits of certain plants e.g. types of plums and apples Pectin forms a gel in water and has uses for setting jam and making various sweet foods. Sometimes used as a vegan alternative to gelatin (also known as gelatine) in the preparation of "set" or glazed foods because the beef (cow) or pork (pig) origin of gelatin is not acceptable as an ingredient in food products to some people. Pectin forms a complex polysaccharide 5. Glycogen The stored form of glucose (glucose is a monosaccharide - see above) present in animals including humans. Energy store within the body, stored within muscles and the liver and brain Humans store sufficient glycogen for 24 hours

For comparison:

Starch is the most common carbohydrate in the human diet. It is one type of polysaccharide. There are many different starches. Their sizes and shapes are characteristic of the plant that produced them, e.g. potatoes, bananas, beans (e.g. lentils, peas and chickpeas), barley, breadfruit, oats, oca, chestnuts, water chestnuts, wheat, yams, corn (maize) and rice. In all cases pure starch is a white, tasteless and odourless powder that is insoluble in cold water or alcohol. Starch is not readily digested by humans but it is more easily digested after it has been cooked in the presence of water e.g. in bread, pancakes, noodles, pasta and porridge.

Glycogen has a similar composition to that of starch. An important difference is that it is made (from glucose) by animals rather than by plants. Although small amounts of glycogen are stored in the body as an energy reserve it is insignificant in terms of humans dietary intake because glycogen stored in animal tissue breaks back down to glucose after an animal's physical death.

Examples of non-starch polysaccharides:

This list of compounds classed as non-starch polysaccarides (NSP)s is not complete but includes examples of common NSPs.

• alginates
• arabinoxylans
• beta-glucans
• cellulose
• chitins
• gellan
• guar
• inulin
• lignin
• pectin
• xanthan

and some other carbohydrates with β-glycosidic linkages.

Some sources also include certain oligosaccharides as 'types of non-starch polysaccharides'. That is understandable because oligosaccharides consist of molecules whose structure is more than two monosaccharide molecules joined together. However, oligosaccharides are increasingly classified separately from polysaccharides so their inclusion in lists of 'examples of NSPs' might cause confusion.

See also dietary fibre, carbohydrates, fatty acids, fats, proteins and water in the diet.