Cereal Chem. 91(5):419-424The firmness of whole beans and of separated embryos and testas from 20 soybean cultivars grown in the same field conditions was estimated after 40 min cooking with AACC International Approved Method 56-36.01. There were considerable variations in the firmness of whole beans, embryos, and testas among cultivars. Testas were much firmer than embryos because of their leathery texture and resistance at slots in the shear cell during compression. For soft cultivars, the firmness after 10 min cooking was also measured, and an apparent first-order reaction kinetics model was applied to estimate the initial firmness at 0 min cooking and the softening rate constant from firmness data after 10 and 40 min cooking. The estimated initial firmness at 0 min cooking and softening rate constant of embryos and testas varied widely among seven cultivars, and these two parameters were considered to be controlled by different genetic mechanisms, because no correlation was found between the parameters. The softening rate constants of testas were much smaller than those of embryos, and the relative firmness of testas to embryos increased during cooking. The firmness of whole beans and embryos after 10 min cooking would be a useful characteristic for approximating their firmness after 40 min cooking.The firmness of cooked beans is an important quality characteristic determining the suitability for food use of soybeans (Glycine max [L.] Merr.). A soft and tender texture is generally preferable for cooked beans used to produce traditional soybean products, such as cooked and seasoned beans (nimame), fermented boiled beans (natto), and fermented bean paste (miso) (Taira 1990). The firmness of whole beans is a key characteristic to be measured and evaluated, because many soybean foods utilize whole beans. However, when the embryos (cotyledons and embryonic axis) of cooked beans have a pleasant soft texture, there is sometimes an unpleasant mouthfeel of the relatively firm testa (seed coat), which remains and packs into the molar teeth, as described by Stanley et al (1989). This sensory experience clearly indicates that cooked beans used as food should have a sufficient softness of the testa as well as the embryo.Legume seeds are composed of three major components: the cotyledon, embryonic axis, and testa (the first two components form the embryo). The embryo is developmentally derived from the zygote, and the testa is derived from integuments of the ovule. Therefore, the characteristics of these two parts are considered to be controlled by various different developmental and genetic mechanisms. All seed components (cotyledons, testa, and embryonic axis) are considered to contribute to the firmness of the cooked bean, but the extent and mechanism of the contribution of each component have not been fully characterized so far. The embryo has the predominant effect on the firmness of the cooked bean, because it is a major part of the seed. To genetically improve the firmness of cooked whole beans, the firmness of each...