Comparison of Different Methods for Determination of Dietary Fiber

Abstract

Abstract Several methods are available for determination of dietary fiber. To increase insight into the relative merits of these methods, the acid-detergent fiber (ADF) and neutral-detergent fiber (NDF) methods of Van Soest et al., the Hellendoorn method, the method of Prosky et al. (AOAC method), and the Englyst method were compared with respect to the amount and the nonstarch polysaccharide (NSP) composition of dietary fiber determined in 4 food products. Our results show that the ADF/NDF detergent methods are inaccurate for the determination of cellulose, hemicellulose, and lignin, and that the NDF and Hellendoorn methods are less-suited for the determination of insoluble dietary fiber. There is a discrepancy between the amount and the NSP composition of the dietary fiber determined by the AOAC and Englyst methods. This is because of either overestimation of the amount of dietary fiber in the AOAC method (coprecipitation of oligosaccharides or Maillard reaction products) or to underestimation of the amount of dietary fiber in the Englyst method (loss of polysaccharides during hydrolysis or derivatization), or both. Differences in isolation methods lead to differences in amounts of soluble and insoluble dietary fiber found by different methods. For both the Englyst and the AOAC methods, calculation of the amount of soluble dietary fiber from the difference between total and insoluble dietary fiber is preferable, because large errors may occur in determining the soluble portion. We have shown that although different methods can yield comparable dietary fiber values, the NSP composition can vary greatly. Therefore, we recommend using those methods that determine specifically well-defined components of the dietary fiber. The chromatographic Englyst method is preferred for this reason, and because it gives insight into the type of polysaccharides present.