Water-soluble Oligosaccharides of Murasakizukin, Immature Black Soybeans (Glycine max Merrill Kuromame Makino), at Different Maturities, and Changes of Their Oligosaccharides by Boiling.

Murasakizukin is a bean eaten as the immature black soybean (Glycine max Merrill Kuromame Makino), of which the name was derived from their characteristic surface color of the cotyledon. The surface color of the cotyledon turns from green to purple during maturation. In this study, we classified their maturity into five stage (stage 1-5) according to their surface colors, and examined the contents of water-soluble oligosaccharides by HPLC. In Murasakizukin, soybean oligosaccharides, raffinose, and stachyose, were detected in the cotylendon from stage 3. Although the contents of these oligosaccharides were decreased by boiling, the increase of the contents of sucrose and maltose were observed, which might contribute to the good taste, sweetness, of Murasakizukin, when eating. The sensory evaluation of the Murasakizukin at different maturities showed no significant differences in preference among them.