Evaluation of AOAC‐Method 2017.16: Detection of Oligosaccharides as Low Molecular Weight Soluble Dietary Fiber

Background and Objectives
In many countries, the Codex Alimentarius definition of dietary fiber has been adopted with the optional inclusion of oligosaccharides with a degree of polymerization (dp) of ≥ 3. These oligosaccharides are usually captured as low molecular weight soluble dietary fiber (LMWSDF). The suitability of the AOAC-method 2017.16 for the determination of LMWSDF was evaluated, focusing on the correct differentiation between LMWSDF and mono- and disaccharides using different groups of oligosaccharides.

Findings
Desalting of LMWSDF with ion exchange resins resulted in an expected, almost complete loss of uronic acid-based oligosaccharides. Due to their elution behavior in size exclusion chromatography, pentotrioses (arabinotriose, xylotriose) were excluded from LMWSDF. Differently, 1,6-linked hexobioses such as melibiose eluted earlier than 1,4-linked hexobioses (such as the standard maltose) and were incorrectly captured as LMWSDF.

Conclusions
A precise determination of LMWSDF content using AOAC-method 2017.16 depends on the sample to be analyzed. As LMWSDF cannot always be analyzed correctly, these data raise additional questions about the suitability of the dietary fiber definition.
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Significance and Novelty
This study indicates that data of the AOAC-method 2017.16 applied to samples containing rather unusual oligosaccharides have to be carefully interpreted.