OBJECTIVE: The objective of this work was to evaluate the protein quality of soybean flours that differs from each other in relation to the presence of lypoxigenases and/or Kunitz's Trypsin Inhibitor. METHODS: Biological assays with rats were carried out to evaluate Protein Efficiency Ratio, Net Protein Ratio, Net Protein Utilization and the digestibility. The determination of the aminoacid composition of the flours and the estimation of Chemical Score Corrected by Digestibility were carried out. RESULTS: The Protein Efficiency Ratio, Net Protein Ratio, Net Protein Utilization values for the soybean varieties were inferior to the values obtained for casein. Higher digestibility values were obtained for the flours lacking Kunitz's Trypsin Inhibitor than for the flours with Kunitz's Trypsin Inhibitor present, and those were very close to the values of casein. About the determination the aminoacid composition it was verified that the restraining amino acid of this soybean is lysine, not methionine, differently from what literature indicates. CONCLUSIONS: The genetic removal of Kunitz's Trypsin Inhibitor improves soybean protein digestibility considerably. Chemical Score Corrected by Digestibility results did not indicate difference between the flours lacking Kunitz's Trypsin Inhibitor and those derived from flours of lines with Kunitz's Trypsin Inhibitor present, as it was observed by the results of in vivo digestibility.
soybeans; Trypsin inhibitors; protein quality; Trypsin inhibitor; Kunitz soybean
