Fiber (Insoluble, Soluble, Total - Resistant Oligosaccharides Method) Test

Method description

This method determines traditional total dietary fiber (TDF), soluble dietary fiber (SDF), insoluble dietary fiber (IDF), and digestion-resistant oligosaccharides (ROs) in both food ingredients and food products. Samples (defatted if necessary) are first run by a traditional dietary fiber method, in which digestion with three enzymes (protease, amylase, and amyloglucosidase) is carried out in a phosphate buffer. Any solid particles not in solution after digestion are considered insoluble dietary fiber and are filtered off and measured gravimetrically. The filtrate from this first filtration is collected and ethanol is added to precipitate the soluble dietary fiber. The soluble fraction is then filtered and measured gravimetrically. The final filtrate solution from the soluble dietary fiber analysis is collected after filtering off the precipitated soluble fiber fraction. Resistant oligosaccharides are soluble in this alcoholic solution, so in order to quantitate them, the filtrate is evaporated to 20 mL. Deionized through a series of anion and cation exchange columns to remove interferences from buffers, salts, amino acids, peptides, and protein and then reconcentrated to 10 mL. The solution is mixed well and syringe filtered prior to analysis by size exclusion HPLC. The size exclusion HPLC columns separate sample solution components into peaks based on molecular weight. The peaks corresponding to oligosaccharides larger than DP2 are quantitated, summed, and reported as total resistant oligosaccharides.

Acceptable matrices

Food and Food Ingredients

Unacceptable matrices

Baking powder, Samples containing more than 2% stevia

Limit of quantitation

Total Dietary Fiber - 0.2% Soluble Fiber – 0.2% Insoluble Fiber – 0.1% Resistant Oligosaccharides - 0.1%

Equipment

General Gravimetric Analytical Chemistry Equipment HPLC-Refractive Index Detector

Method reference

AOAC 2001.03 with AOAC 991.43 digestion

Reportable unit

%

Sample size requirements

25 g

Information required by submitter

please supply expected estimates. Indicate matrix type, and indicate if samples are high in fat (>5% fat). Indicate whether the sample contains stevia, fructans (inulin or fructooligosaccharides (FOS)), psyllium, flax, and gum (i.e. guar gum)

Additional information

This test is ISO/IEC 17025 accredited through A2LA, Certificate # 2769.01. Dietary Fiber is the portion of the carbohydrates which is not digested in the human gut. It is composed of both soluble and insoluble components. These methods are applicable to all food products, however samples containing psyllium or fructans should be submitted under specific test codes. High-fat (>5%) samples require special handling. Resistant oligosaccharides are polysaccharides from DP3 and higher which are soluble in ethanol and are resistant to digestion by amylase under the conditions of the traditional dietary fiber analysis (AOAC 991.43). In the past, this analysis has gone by names such as “fibersol” and “resistant maltodextrins.” At Medallion Labs, we feel that these terms are limiting because we know that other polysaccharides, such as polyfructans are also included in this result. We are using AOAC method 2001.03, but have renamed the result “resistant oligosaccharides” because we feel this is the proper, general classification for the molecules that are being measured.