DETERMINATION OF SOLUBLE DIETARY FIBER IN FOODS AND FOOD-PRODUCTS - COLLABORATIVE STUDY

A collaborative study was conducted to determine the soluble dietary fiber (SDF) content of foods and food products by using a combination of enzymatic and gravimetric procedures. The method was basically the same as that employed for determining total dietary fiber (TDF), 985.29, and the method for insoluble dietary fiber (IDF), 991.42. Ten laboratories were each sent 13 test samples (6 blind duplicates and 1 standard [green beans] containing 29-33% TDF, 19-23% IDF, and 8-13% SDF) and were instructed to assay for IDF, SDF, and TDF independently. Included in the package were the 3 enzymes, namely alpha-amylase, amyloglucosidase, and protease, and the filter aid Celite, which was thought to be the major cause of high reproducibility relative standard deviation (RSD(R)) values for SDF obtained in a previous collaborative study. The foods to be analyzed were apricots, carrots, chickpeas, onions, raisins, and the sugar beet fiber Fibrex(TM). IDF, TDF, and SDF were calculated as the weight of residue minus the weight of protein and ash on a dry weight basis. RSD(R) values of the IDF results averaged 8.02%, with only 1 food having an RSD(R) >10%. The RSD(R) values for the TDF results averaged 4.97%, and all foods had an RSD(R) <7%. Although the RSD(R) values for SDF averaged 14.17%, 4 of the 6 foods had an RSD(R) <10%, and 1 of the 2 remaining foods that had a high RSD(R) had an SDF content of only 1.2%. In all cases, the RSD(R) values of the SDF content of the foods were less than the values for the same foods analyzed in a previous collaborative trial. The enzymatic-gravimetric method for the determination of SDF was adopted first action by AOAC INTERNATIONAL.