Methods to determine food inulin and oligofructose

The fructans, inulin and oligofructose, were known to possess many of the physiologic properties of dietary fiber (DF) but were not listed as DF on the labels of foods that contained them because they did not precipitate in 78% ethanol as prescribed in the AOAC International methods for DF. In the latter part of 1995, the Food and Drug Administration (FDA) agreed to consider fructans as DF if an AOAC-accepted analytical method could be successfully developed for fructans. Six blind duplicate pairs of foods, containing from 4 to 40% of inulin or oligofructose, were sent to nine collaborators in five countries for assay. These foods included a low fat spread, cheese spread, chocolate, wine gum, dry ice mix powder and biscuits. In the proposed method, the samples were treated with amyloglucosidase and inulinase, and the sugars released were determined by ion-exchange chromatography. The concentration of the fructan was calculated by the difference in sugars present in the two enzymic treatments and the initial sample. The repeatability standard deviations (RSDr) for the inulin and oligofructose ranged from 2.9 to 5.8% and the reproducibility standard deviations (RSDR) for these fructans ranged from 4.7 to 11.1%. The method was accepted by the AOAC as an official first action.