Dietary fibers from soybean cotyledons classified as original (ODF) and milled (MDF) were fractionated and evaluated as to fractions and monosaccharide composition. The major constituent was hemicellulose, 59% in ODF and 51% MDF, pectin was in average 14% and cellulose, 8.5%. Both samples had 17 mg.g-1 uronic acids and the same composition in monosaccharides: galactose, glucose and arabinose/rhamnose, after hydrolysis. Protein fractions extracted from protein concentrate, defatted flour and dietary fibers were evaluated for protein solubility in different solvents (NaCl, water, ethanol and NaOH) and for molecular weight. Defatted flour had the highest concentration of proteins soluble in saline solution, while protein concentrate and dietary fibers had the highest protein solubility in alkaline solution. Residual protein, not extracted with any of the solvents used, remained in the insoluble fraction and the highest concentration was in the protein concentrate, followed by MDF, defatted flour and ODF. Protein electrophoresis of the four food ingredients showed subunits that constitute the fractions β-conglycinin and glycinin. Protein extracted from the dietary fibers showed bands with molecular weight of about 30 kDa, probably glycoproteins from cell wall material, rich in hydroxyproline.
cell wall fractionation; monosaccharides; uronic acids; protein classification; electrophoresis; hydroxyproline
