Dietary Fiber Analysis as Non‐Starch Polysaccharides

Abstract

AbstractThe original hypothesis on fiber, that a diet with a high content of unrefined plant foods was linked to a low incidence of Western diseases, has been largely confirmed. The plant cell wall encapsulates and thus controls the release of nutrients, including free sugars and starch, from the plant tissue and thereby influences the glycemic response. This ability to influence digestion and absorption, and thus the physiological effects of other nutrients, is an important property of dietary fiber. The other main properties of a high‐fiber diet are increased fermentation and fecal bulk, and binding of potentially toxic substances, e.g. lectins, thus affecting large gut physiology and health. Naturally high‐fiber diets have low contents of fat and sodium, and are a good source of vitamins and minerals. The national dietary guidelines recommend a diet rich in fruit, vegetables and whole‐grain cereals, and thus naturally rich in plant cell‐wall material, the major constituents (approximately 90%) of which are nonstarch polysaccharides (NSP). Food labeling for dietary fiber should help the consumer in the choice of the recommended unfortified, high‐fiber diet. Analysis of NSP represents a good measure of endogenous plant cell‐wall material for most plant foods and NSP values thus provide a very good marker for a high‐fiber diet.The Englyst procedure for the measurement of dietary fiber as NSP involves enzymatic hydrolysis of starch, precipitation of NSP in ethanol, acid hydrolysis of the NSP and measurement of the released constituent sugars by gas–liquid chromatography (GLC), high‐performance liquid chromatography (HPLC) or colorimetry. Values for total, soluble and insoluble NSP may be obtained using any of the end‐point techniques. The detailed information obtained from the chromatographic methods, which identify and quantify the individual constituent sugars, is particularly useful in studies of the relation between intakes of NSP and health; values for the constituent NSP sugars have been published for a wide range of foods.