Color, trypsin inhibitor and urease activity [soybean meal] as it affects growth of broilers

In five experiments, the relationships among trypsin inhibitor contents, urease index and color in soybean meal (SBM), and the effects of those relationships on broiler chick performance were determined. Raw, solvent‐extracted SBM was dehydrated to 2% moisture; then 0, 4, 8, 12, or 16% moisture was added and autoclaved at 120 C in sealed containers from 0 to 135 min with 15‐min intervals. Urease and trypsin inhibitor contents decreased with either increasing moisture content or cooking time. With 16% added moisture, 30 min of cooking time was required to decrease urease index to an acceptable level, and 45 min was required to decrease trypsin inhibitor contents. Raw SBM autoclaved with less than 12% added moisture contained urease and trypsin‐inhibitor contents that were not considered undesirable, regardless of cooking time used. Increased moisture and cooking time resulted in decreased trypsin inhibitor and urease contents, increased broiler growth, improved feed efficiency and decreased pancreas hypertrophy. Commercial SBM, containing 12 ug trypsin inhibited per mg of protein (µ/mg), a tristimulus+α (redness) color value of +3.21, and a urease index of 0.19 ΔpH, was autoclaved for 0–25 min with 5‐min intervals to determine the effect of additional heat on broiler performance and SBM color. The commercial SBM, heated an additional 10 min, contained 1.77 µg trypgin inhibitor per mg of protein, a+a color value of +4.76, and urease index of 0.02 ΔpH. Broiler growth and feed efficiency were improved when the commercial SBM was heated an additional 10 min. Results of this study show that color is a good predictor of trypsin‐inhibitor content and broiler chick performance. Color may be used to predict underprocessing, adequate, and overprocessing of SBM; however, trypsin inhibitor and urease index do not show the effect of overprocessing.