Development of Breeding Method by Controlling Lipoxygenase Activity in Soybeans for Rising and Diversifying the Taste and Flavor of Tofu.

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Examination of lipoxygenase (Lox) activity of soybean varieties produced in breeding stations throughout Japan showed that there is a marked tendency for higher Lox activities at the both of pH 7.0 and pH 9.0 in the varieties produced in cool regions than those produced in warm regions. We found that cv.Shintanbaguro has low levels of Lox activity. Genetic study revealed that the low Lox activity of cv.Shintanbaguro is due to genetic factor(s).By the use of single nucleotide polymorphisms (SNPs) of the DNA sequences of structural gene and of promoter region, we developed DNA marker of L2 gene and L3 gene to breed effectively the lipoxygenase lacking variety of various types.We analyzed oxylipin metabolism in soybean homogenates containing different set of lipoxygenase isozymes (L1, L2 and L3), namely, Suzuyutaka (L-123) ; Yumeyutaka (L-1) ; Kanto102 (L-2) ; Kyushu119 (L-3) ; and Ichihime (lacks all the three isozymes : L-0). With every cultivar, amounts of oxidized fatty acids in ester … More ified form were higher than those in free form. Kanto102 formed highest amounts of oxidized lipids, and Yumeyutaka and Ishihime formed the lowest. With Kanto102 and Kyushu119 high amounts of keto fatty acids were formed, while they were undetectable with Yumeyutaka and Ichihime. Lower amounts of oxidized lipids again made Yumeyutaka and Ichihime good cultivar for food processing.Using normal (L-123) and Lox-deficient (L-1, L-2, L-3, L-0) lines of soybeans, the aroma constituents of tofu were investigated. The aroma constituents, especially hexanal, 1-hexanol and hexanoic acid were contained more amounts in the tofus made from L-123 and L-2 compared with those of the other Lox-deficient lines (LOX-1, LOX-3, LOX-0). The tofu prepared by the non heat-squeezing method contained more hexanoic acid and tasted more mouthful (rich) and sweeter compared with that by the heat-squeezing method. The amounts of hexanal, hexanoic acid and maltol increased in the tofu made from the stored soybean under the condition of higher temperature and humidity. This means that the harvest and storage condition of soybeans is important factors affecting the flavor of tofu.From the above results it can be concluded that manipulation of Lox activity in soybeans enables us to diversify the taste and flavor of tofu. Less