Determination of oligofructose, a soluble dietary fiber, by high-temperature capillary gas chromatography.

A high-temperature capillary gas chromatographic method was developed for the quantitative determination of oligofructose in foods and food products. Sample preparation involves oxymation and silylation of the extracted sugars. The oximetrimethylsilyl derivatives are analyzed on an apolar capillary column, with detection by flame ionization. The method is accurate, with recovery of spiked samples at >96%. Repeatability was excellent; RSD values of 1.1% were obtained. Other common oligosaccharides, such as malto-, isomalto-, and galactooligosaccharides, and levan do not interfere, making the method specific and reliable.

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.

On the presence of inulin and oligofructose as natural ingredients in the western diet.

The classic definitions of inulin and oligofructose are constructively criticized. It is observed that inulin cannot unequivocally be described as a polydisperse 1-kestose-based (GFn) beta (2-->1) linear fructan chain, but that inulin always contains small amounts of Fm and branched molecules. This review article describes the presence of inulin and oligofructose in common foodstuffs. Historical data on human consumption add an extra dimension. Modern analytical techniques (HPLC, LGC, HPAEC-PAD) are used to check the variety of data mentioned in the literature throughout the past century. Methods to determine inulin and oligofructose in natural foodstuffs (cereals, fruit, and vegetables) are optimized and used to determine the loss of inulin during storage and during preparation of the food. These findings allow quantification of the amount of inulin and oligofructose in the average daily western diet. The daily per capita intake is estimated to range from 1 to 10 g, depending on geographic, demographic, and other related parameters (age, sex, season, etc.). Inulin and oligofructose are not measured by classic methods of dietary fiber analysis and consequently are often not mentioned in food tables. Their significant contribution (1 to 10 g/d/per capita) to the dietary fiber fraction (recommended at 25 g/d/per capita) is not taken into account in any nutritional recommendations. In view of this, inulin and oligofructose deserve more attention, both in food composition tables and in diet or nutrition studies.