Measuring dietary fiber

Abstract

In this review of methods for fiber analysis, selected steps were evaluated and different methods of analysis were compared. Efficacy of starch hydrolysis from peas after a short incubation with pepsin, pH 1.5, was comparable to that obtained after treatment with DMSO. A single step hydrolysis with dilute sulfuric acid was adequate to hydrolyze the soluble fraction of fiber. Replacement of a secondary step of 3 h at 100°C with one of 0.5 h at 121°C had no effect on the yield or composition of the insoluble fraction of fiber. Chemical analysis of neutral detergent fiber residues suggests that for a few foods the neutral sugar and uronic acid composition and yield are similar to those obtained upon analysis of the insoluble fraction of dietary fiber recovered by the methods of Theander and Southgate. Chemical analysis of total dietary fiber residues obtained by the AOAC gravimetric procedure indicate that when food containing substantial amounts of simple sugars are analyzed, some of these sugars are recovered in the 80% ethanol insoluble fiber residue and inflate the fiber value. A major cause of differences among the four methods of analysis that were compared was in the recovery of material insoluble in 72% sulfuric acid, i.e. Klason lignin. Indirect evidence suggests that in some instances, this material represents Maillard reaction products and in others, unhydrolyzed protein.