RESEARCH ON SOME CHEMICAL ANALYSIS METHODS FOR EVALUATING THE SOYBEAN MEAL QUALITY

Rodica Caprita, A. Caprita

Abstract
Heat treatment of soybeans can reduce the activity of trypsin inhibitors and thereby improve the digestibility of protein. Overheating, however, may destroy or reduce the availability of certain heat sensitive amino acids and reduce the nutritional value of soy protein. The objective of our study was to compare three different chemical analysis methods for evaluating the soybean meal quality, and to establish the most suitable for evaluating over processing. Commercial SBM and raw soybean (granulation 200μ) were heated in a forced air oven at 120 °C for varying periods: 5, 10, 15, 20, 25, and 30 minutes. The urease index (UI), the KOH protein solubility and the Protein Dispersibility Index (PDI) were determined. Protein was determined by the burette method. We observed that the UI is useful to determine if the soybean meal has been heated enough to reduce the antinutritional factors, but it is not very useful for determining if soybean meal has been over-processed. A UI value of zero does not necessarily indicate over processing of SMB. KOH protein solubility is not a sensitive index for monitoring under processing of soybean meal. The KOH protein solubility changed very little up to first 10 minutes of heating and then decreased to a solubility of 65.20%. The PDI is the best method of evaluating these soybean ingredients for both under heating and over heating. PDI decreased incrementally from 78% to 20% for the heating times from 0 to 30 minutes. PDI is also the simplest measurement procedure of those that were evaluated.

Key words: urease index, protein solubility, soybean meal, protein digestibility