Research at the University of Illinois is investigating variation in the protein quality of soybean meal used in poultry ration formulations. Dr. Carl Parsons indicated in an article that soybean meal (SBM) is the most important source of dietary protein in poultry in the U.S. and most of the world. Even though SBM is one of the highest quality protein sources, variation in quality can be seen in the crude protein, amino acid levels and in the digestibility of the amino acids in SBM. Either insufficient heating (underprocessing) or excessive heating (overprocessing) will negatively impact amino acid digestibility. Overprocessing was shown to reduce the concentrations and digestibility of lysine and cystine, but did not reduce methionine or threonine levels.
The paper compared four assays used to detect differences in SBM quality. The urease assay is correlated to the destruction of trypsin inhibitors and lectins in SBM. The KOH protein solubility test is useful in detecting excess heating or overprocessing of SBM. The protein dispersibility index (PDI) and nitrogen solubility index (NSI) measure protein solubility in water. Dr. Parsons conducted several chick studies with SBM that was damaged by excessive autoclaving for different lengths of time. Results indicated that properly processed SBM might have an optimum urease value of 0.05-0.2 and the KOH solubility in the range of 70-85 percent. They found that DPI may be more sensitive than urease or KOH indexes for detecting the minimum heat needed to process SBM. Additional research is needed that compares commercial SBM with different PDIs in order to establish the optimum PDI value range for meals in poultry diet formulation.
Parsons, Carl M., 1998. Variation in protein quality of soybean meal for poultry. Proceeding Arkansas Nutrition Conference, September 15-17.