Determination of the non-starch polysaccharides in plant foods by gas-liquid chromatography of constituent sugars as alditol acetates
A method is reported for the measurement of non-starch polysaccharides (NSP) from plant foods. NSP are the major components of “dietary fibre.” The polysaccharides are divided into cellulose and non-cellulosic material and the constituent sugars are determined by gas-liquid chromatography. Starch is removed, after gelatinisation, by incubation with hog pancreatic α-amylase together with pullulanase. The enzyme preparations are shown to be specific for the hydrolysis of α-1,4- and α-1,6-glucosidic bonds, and not to affect NSP. The starch-free material is then analysed by three separate but complementary procedures: (A) hydrolysis with 1 M sulphuric acid after solubilisation of cellulose with 12 M sulphuric acid; (B) hydrolysis with 1 M sulphuric acid; and (C) extraction with phosphate buffer at pH 7 and 100 °C, solubilisation of cellulose with 12 M sulphuric acid and then hydrolysis with 1 M sulphuric acid. Neutral sugars are measured by gas-liquid chromatography as alditol acetates and uronic acids by a colorimetric method. Starch made resistant to α-amylase digestion by food processing is identified by additional steps in procedure B, and measured as “resistant starch.” Procedure A gives total NSP and procedure B neutral non-cellulosic polysaccharides. A value for cellulose is obtained as the difference between glucose measured in procedures A and B. Procedure C gives NSP insoluble in phosphate buffer at pH 7. Soluble NSP is the difference between total NSP and insoluble NSP. Results for the NSP analysis of selected foods are given.