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Resumen:
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Three experiments were conducted to compare urease activity (UA), orange G-binding capacity (OGBC), and protein solubility (PS) in a potassium-hydroxide solution of soybean meal (SBM) as indicators of overprocessing. In two additional experiments, amino-acid supplementation was employed in an attempt to overcome the growth depression associated with overheating SBM. Subsamples of commercially prepared lots of dehulled SBM were heated for varying periods of time in an autoclave at 121 C. In Experiments 1, 2, and 3, UA dropped to zero (pH change) after approximately 10 min of cooking. The assay was unable to differentiate between meals that were heated for longer periods. The OGBC of SBM was decreased by autoclaving. However, the narrow range of the orange G values that corresponded to degrees of heat treatment indicated that this test may be of limited value in identifying overprocessed SBM. By contrast, PS values decreased with each increase of autoclaving time, and did not approach zero even with 80 min of heating. Adding .2 % lysine either singly or in combination with .2% arginine or. 1% methionine, or both, totally overcame the growth depression due to overprocessing. The weight gains and feed conversions of broiler chicks were negatively correlated with autoclaving times in excess of 10 minutes. In all experiments, PS values more closely reflected the impaired chick performance from overheated SBM than UA or OGBC. The PS values below 70% suggested overprocessed SBM.
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