Enzymatic hydrolyses of fibers from soy cotyledons and characterization of solid and soluble fractions

The objective of this work was to determine the best enzymatic hydrolysis conditions for dietary fiber from soybean cotyledons, original (ODF) and milled (MDF), and to characterize the solid and soluble hydrolytes. The samples were hydrolyzed with carbohydrase (200 mu L g(-1) for 12 hours, at 30 degrees C) or protease (150 mu L g(-1) for 5 hours, at 55 degrees C). The solid fraction of the samples treated with carbohydrase had a reduction of 73% for the carbohydrates and of 50% for the uronic acids of the initial material; there was an increase in protein concentration and in solubility and swelling volume in comparison to the nonhydrolyzed material. Soybean storage proteins - beta-conglycinin and glycinin - were extracted from nonhydrolyzed dietary fiber and identified by electrophoresis. Protease solubilized 54% of the sample's total protein content, formed peptides with molecular weight lower than 10 KDa, a band with molecular weight of 25 KDa probably cell-wall glycoprotein, and left a solid fraction with 76% total dietary fiber. Scanning electron microscopy showed physical alterations for ODF hydrolyzed with protease, with more superficial pores than MDF. The enzymatic treatment was effective in altering the chemical and structural composition of the fibers, resulting in new perspectives for technological applications.