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Variation in Firmness of Whole Beans, Embryos, and Testas of Cooked Soybean (Glycine max) Cultivars

¹NARO Institute of Crop Science, 1-18, Kannondai 2-chome, Tsukuba, Ibaraki 305-8518, Japan. ²Corresponding author. Phone: +81-29-838-8503. Fax: +81-29-838-7488. E-mail: yas@affrc.go.jp ³National Food Research Institute, 1-12, Kannondai 2-chome, Tsukuba, Ibaraki 305-8642, Japan.

The 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.