The analysis of dietary fibre—the choices for the analyst

Abstract The analysis of dietary fibre (which is defined as the sum of lignin and the polysaccharides not digested by the endogenous secretions of the human digestive tract) presents several problems to the analyst. Dietary fibre is a mixture of substances derived from the structural materials of the plant cell wall and a range of polysaccharides of a non‐structural nature either present naturally in foods or derived from food additives. The complete analysis of such a complex mixture would be difficult and time consuming and a number of practical alternatives have been used. These include methods based on the enzymatic removal of protein and starch to give an ‚indigestible residue’︁ and procedures based on extraction with neutral detergent solutions. These procedures in their present form do not measure water‐soluble components and therefore underestimate dietary fibre. More detailed methods in which the water‐soluble and water‐insoluble non‐cellulosic polysaccharides, cellulose and lignin were measured separately are described. In these the non‐cellulosic fraction was characterised in terms of its component sugars. It is suggested that methods of this type are necessary to characterise dietary fibre analytically in order to account for the properties of dietary fibre.