Determination of dietary fibre as non-starch polysaccharides with gas–liquid chromatographic, high-performance liquid chromatographic or spectrophotometric measurement of constituent sugars
Methods for the measurement of dietary fibre as non-starch polysaccharides (NSP) are described. A common enzymic removal of starch and acid hydrolysis of the NSP to their constituent sugars are followed by one of three alternative techniques, gas–liquid chromatography, high-performance liquid chromatography or spectrophotometry, for measurement of the released sugars. The results obtained by the three methods are in good agreement for a wide range of raw and processed foods. NSP compose approximately 90% of the plant cell-wall material and are therefore a good index of this material. Values for NSP therefore provide a good marker for a diet rich in fruit, vegetables and high-extraction cereal products associated with health and recommended in dietary guidelines. Values for total, soluble and insoluble NSP may be obtained with any of the end-point techniques, and the detailed information obtained from the chromatographic methods is useful in studies of the relationship between the intakes of various types of NSP and health. The causes of some potential interferences in the spectrophotometric assay, especially from processed foods, have been identified and eliminated. The rapid spectrophotometric version is suitable for food labelling purposes and for quality control, and the changes described have made it more robust.