2026 Volume 95 Issue 2 Pages 162-168
Seed coat cracking of black soybeans during processing, resulting from microscopic seed coat crazing during harvesting and threshing, reduces product yield. We found that the occurrence of this crazing by an external force was affected by seed moisture content and differed with the cultivar and line. To breed cultivars resistant to this crazing, we developed a method to evaluate the resistance to seed coat cracking during processing. This method evaluates resistance using the external force tolerance index (EFTI), which is calculated from the ratio of beans exhibiting seed coat breakage after the application of an external force followed by immersion in water. The results of this evaluation for seven black soybean cultivars showed differences in EFTI at 9% and 14% moisture content levels. The EFTI at 9% moisture content is useful for assessing the risk of seed coat crazing during harvesting and threshing under excessively dry conditions, whereas the EFTI at 14% moisture content is useful for evaluating the risk under the recommended harvesting conditions. An appropriate amount of silica gel can be applied to adjust the evaluation samples to the target moisture content (9%, 14%). The required amount is calculated based on the original moisture content and the sample weight. Because of interannual differences in EFTI, multiyear trends should be analyzed using raw materials grown, harvested, and threshed under the same conditions.
