DETERMINATION OF THE TOTAL PEPSIN-PANCREATIN INDIGESTIBLE CONTENT (DIETARY FIBER) OF SOYBEAN PRODUCTS, WHEAT BRAN, AND CORN BRAN

Successive pepsin and pancreatin digestions were used to determine indigestible content (IDC) of various soybean products and cereal brans. IDC included insoluble material as well as solubilized carbohydrate and protein separated by ultrafiltration (molecular weight above 5000). Total IDC as percent of dry matter was: corn bran, 97; soybean hulls, 86; wheat bran, 52; whole soybean, 23; soy protein concentrate, 40; and defatted soy flakes, 16. The IDC values include 3-25% soluble material recovered by ultrafiltration. Chemical analyses of the insoluble nondigestible fraction from soybean hulls indicated a composition of 71% cellulose, 20% hemicellulose, 9% lignin plus ash. The percent protein digestibility was estimated as: whole soybean, 68; defatted soy flakes, 81; soybean hulls, 60; soy protein concentrate, 61; corn bran, 43; and wheat bran, 60. The large values for undigested protein in soy protein products were unexpected. © 1979, American Chemical Society. All rights reserved.