J. M. Pollock and W. F. Geddes. Copyright 1960 by the American Association of Cereal Chemists, Inc.
An unheated, defatted soy flour was fractionated by mild solvent separation, precipitation, and dialysis techniques. The baking performance of the flour and its fractions, employed at a level of 3% (wheat flour basis), was tested by a small scale procedure using several levels of potassium bromate. Chemical studies were made on the fractions in an attempt to relate their composition to baking performance. The raw soy flour caused reproducible adverse effects on leaf volume, but appropriate heat treatment improved loaf volume when baked with a satisfactory level of bromate. Heat treatment of several fractions adversely affected loaf volume; others were not significantly influenced, and one was improved. The most injurious fractions were encountered in the dialysate from the supernatant after precipitation of most of the protein at pH 4.2 from the water-soluble fraction. Still another dialysate fraction contained most of the undesirable flour, although it was otherwise of fair baking quality. A protein fraction, not preciptated at pH 4.2, was excellent in baking quality and showed high antitryptic activity. Analyses of various fractions demonstrated that chlorides, sugars, and sulfhydryl groups were not responsible for the poor baking quality of the fractions in which they were found. Effects of fractions on dough pH were eliminated as a cause of poor baking quality. Quantitative analysis of the two most injurious fractions indicated significant levels of zinc, calcium, magnesium, and phosphate ions. In baking tests only zinc and phosphate ions corresponding to the levels in 3% of the most injurious fraction were found harmful. Zinc and phosphate ions in the amounts employed in the baking tests (0.0048 and 0.60%, respectively, flour basis) retarded gas production; whereas the adverse effects of raw soy flour itself, and of the acid-precipitable protein, were primarily on gas retention. Thus, the inorganic constituents may be of relatively little importance in the performance of soy flour itself.