Nutritional improvement of soy flour

Heating soy flour at 45 degrees C in pH 8.5 Tris buffer for 1 hour in the presence of cysteine or N-acetylcysteine followed by dialysis to remove unreacted thiols resulted in the introduction of new half-cystine residues and lowered trypsin inhibitor content from 37.5 to 6.8 or 4.8 mg/g, respectively, compared to only 14.8 mg/g in the absence of sulfhydryl compounds. Presence of cysteine or N-acetylcysteine during treatment increased protein efficiency ratio (PER) from 0.95 to 2.01 or 2.20, respectively. Corresponding values at 65 degrees C are 1.61, 2.43 and 2.02; and at 75 degrees C, 2.14, 2.53 and 3.19, respectively. Proteins are modified through formation of mixed disulfide bonds, which leads to loss of inhibitory activity and increased protein digestibility and nutritive value.