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 (RSDR) values for SDS obtained in a previous collaborative study. The foods to be analyzed were apricots, carrots, chickpeas, onions, raisins, and the sugar beet fiber Fibrex. IDF, TDF, and SDF were calculated as the weight of residue minus the weight of protein and ash on a dry weight basis. RSDR values of the IDF results averaged 8.02%, with only 1 food having an RSDR > 10%. The RSDR values for the TDF results averaged 4.97%, and all foods had an RSDR < 7%. Although the RSDR values for SDF averaged 14.17%, 4 of the 6 foods had an RSDR < 10%, and 1 of the 2 remaining foods that had a high RSDR had an SDF content of only 1.2%.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of insoluble, soluble, and total dietary fiber in foods and food products: interlaboratory study.

A collaborative study was conducted to determine the insoluble dietary fiber (IDF), soluble dietary fiber (SDF), and total dietary fiber (TDF) content of food and food products by using a combination of enzymatic and gravimetric procedures. The method was basically the same as that developed for TDF only, which was adopted official final action by AOAC, except for changing the concentration of buffer and base and substituting hydrochloric acid for phosphoric acid. These changes were made to improve the robustness of the method. Duplicate blind samples of soy isolate, white wheat flour, rye bread, potatoes, rice, corn bran, oats, Fabulous Fiber, wheat bran, and a high fiber cereal were analyzed by 13 collaborators. Dietary fiber values (IDF, SDF, and TDF) were calculated as the weight of residue minus the weight of protein and ash. The coefficients of variation (CVs) of both the independent TDF determination and the sum of IDF and SDF were better than 15 and 18%, respectively, with the exception of rice and soy isolate. These 2 foods, however, contained only about 1% TDF. The CVs of the IDF were equally good, except for Fabulous Fiber, for which filtration problems occurred. The CVs for the SDF were somewhat high, but these products had very low SDF content. There was excellent agreement between the TDF determined independently and the TDF determined by summing the IDF and SDF. The method for separate determination of IDF and SDF requires further study. The modifications (changes in concentration of buffer and base and the use of hydrochloric acid instead of phosphoric acid) to the official final action method for TDF have been adopted.

Determination of total dietary fiber in foods and food products: collaborative study.

A collaborative study was conducted to determine the total dietary fiber (TDF) content of food and food products, using a combination of enzymatic and gravimetric procedures. The method was basically the same as published earlier (J. Assoc. Off. Anal. Chem. (1984) 67, 1044-1052), with changes in the concentration of alcohol and buffers, time of incubation, sample preparation, and some explanatory notes, all with the intent of decreasing the coefficient of variation (CV) of the method. Duplicate blind samples of soy isolate, white wheat flour, rye bread, potatoes, rice, wheat bran, oats, corn bran, and whole wheat flour were analyzed by 9 collaborators. TDF was calculated as the weight of the residue minus the weight of protein and ash. CV values of the data from all laboratories for 7 of the samples ranged from 1.56 to 9.80%. The rice and soy isolate samples had CV values of 53.71% and 66.25%, respectively; however, each sample contained only about 1% TDF. The enzymatic-gravimetric method for determining TDF has been adopted official first action.

Comparative effects of chitosan and cholestyramine on lymphatic absorption of lipids in the rat.

The effects of chitosan and cholestyramine on intestinal absorption of oleic acid and cholesterol were assessed in adult male rats with cannulae in the thoracic duct lymphatic channel. In acute studies, 50 mg of either cholestyramine or chitosan were included in the test emulsion for intragastric administration. Over a 24-h lymph collection period, cholestyramine caused a 47% depression of cholesterol absorption and a 32% interference with oleic acid absorption. Chitosan had a similar effect on the absorption of both lipids under these conditions (51 and 41% depression, respectively). Studies were also conducted in animals fed for 4 wk on defined diets containing 1 and 5% levels of the test materials. Absorption of lipids from the standard aqueous emulsion was tested in lymph duct cannulated rats which had been fasted overnight. In these animals, prefeeding either cholestyramine or chitosan at the 1% level caused an 18 to 28% reduction in absorption of both lipids with greater variability in the chitosan-fed group. When either test material was fed at the 5% level, absorption of cholesterol was reduced by 63 to 69% and absorption of oleic acid by 58 to 62%. Although these agents may act by different mechanisms, the data suggest that chitosan is as effective as cholestyramine in its acute effects on lipid absorption and that, with chronic feeding, both materials cause equivalent adaptive changes in intestinal transport of administered fatty acid and cholesterol.