COMPARISON OF A COMMERCIAL SOYBEAN CULTIVAR AND AN ISOLINE LACKING THE KUNITZ TRYPSIN-INHIBITOR - COMPOSITION, NUTRITIONAL-VALUE, AND EFFECTS OF HEATING

The content and heat stability of protease inhibitors of a standard cultivar (Williams 82) and an isoline (L81-4590) lacking the Kunitz trypsin inhibitor (KTI) were measured by using enzyme inhibition and enzyme-linked immunosorbent assays (ELISA). The KTI content of the isoline was less than 0.2% compared to Williams 82, with the exact content depending on the extent of cross-pollination of the soybeans. Steam heating of the isoline flour (121-degrees-C, 20 min) resulted in a near-zero level of trypsin inhibitory activity, while 20% remained in the Williams 82 sample. The raw soy flour prepared from the isoline was nutritionally superior to the raw flour prepared from the standard variety, as measured by PER and pancreatic weights. The increased PER was likely due to the lower level of trypsin inhibitory activity in the isoline. Steam heating the flours for up to 30 min at 121-degrees-C progressively increased the PER for both strains. Screening of several accessions from the USDA Soybean Germplasm Collection showed variation in the content of trypsin inhibitor, sulfur amino acids, and lectins, indicating that further screening studies could lead to the discovery of soybeans which yield flour that is safe and nutritious, with minimal heating.