Evaluation of Protein Solubility as an Indicator of Underprocessing of Soybean Meal

Abstract

Two experiments were conducted to compare urease activity, orange G-binding capacity, trypsin inhibitor activity (TIA), and protein solubility (PS) in a potassium hydroxide solution as indicators of underprocessed soybean meal (SBM). Subsamples of raw dehulled, hexane-extracted SBM (RSBM) were autoclaved for varying lengths of time at 121 C. Orange G binding capacity of the meal did not vary substantially and did not clearly differentiate between raw and heated SBM. Urease activity, TIA, and PS all reflected degrees of heat treatment. However, PS values were more closely correlated with chick performance and paralleled with trypsin inhibitor concentration in meals for all autoclaving times used. Chick growth was optimized when RSBM was autoclaved for 15 min with a resulting PS of 75%. Diets containing this meal gave lowest pancreas weight (as percentage of body weight). It appears that PS is of value in the detection of underprocessed SBM. Protein solubility values in excess of 85% or less than 70% indicate under- or overprocessing of SBM, respectively.