Antinutrient occurrence and some physicochemical properties of the protein fractions of five Brazilian soybean varieties.

Protein solubility under different pH conditions, amino acid composition of proteins in the flours, and proteins isolated at a pH of 4.5 (P.I.), as well as trypsin inhibitor and hemagglutinin activities were studied in five Brazilian soybean varieties. The levels of protein and non-protein amino compounds were similar for all varieties. More protein was extracted in slightly alkaline (pH 8.5) water solution than with plain water. Lowering the pH of the extract to 4.5 caused the precipitation of 83% to 86% of the protein. Of the nitrogen remaining in the whey 31% to 39% could be precipitated with 5% trichloroacetic acid. Protein isolated inhibited amino acid patterns similar to those of defatted flours. Trypsin inhibitor activities were higher in the plain water extracts than in the extracts at pH 8.5. Most of the trypsin inhibitory activity was associated with the whey fraction, soluble at a pH of 4.5, while the hemagglutinin activities decreased considerably in the pH 4.5 supernatant, indicating precipitation of the hemagglutinins in this pH.