Factors affecting the isoflavone contents of soybean seeds were studied. Isoflavone contents of seeds of varieties grown at different locations, on different planting dates, and under different temperatures during seed development were determined by HPLC analysis. Fatty acid composition and contents of DDMP-conjugated saponin were also analyzed. The isoflavone content, together with the ratio of linoleic plus linolenic acid to total fatty acid, significantly decreased in the seeds harvested after growth at a high temperature for all soybean varieties tested. A general decrease was observed for all isoflavones, rather than a decrease restricted to a single molecular species. Of the total seed isoflavones, 80-90% were located in cotyledons, with the remainder in the hypocotyls. The hypocotyls had a higher concentration of isoflavones on a weight basis compared with cotyledons. While the isoflavone content of cotyledons exhibited large changes in response to high temperature during seed development, the isoflavone content remained high in the hypocotyls. As previously reported for other saponins, the DDMP-conjugated saponin content of seeds remained stable in response to elevated temperatures during seed development. These studies provide a basis for attempts to improve seed quality by the reduction of isoflavone content.

The isoflavone constituents in soybean seeds were investigated, and 9 kinds of isoflavone glycosides were isolated from the hypocotyls of soybean seeds. Three kinds were proved to be malonylated soybean isoflavones named 6"-0-malonyldaidzin, 6"-O-malonylglycitin and 6"-0-malonylgenistin by UV, MS, IR and NMR.The malonylated isoflavone glycosides as major isoflavone constituents in soybean seed were thermally unstable, and were converted into their corresponding isoflavone glycosides. All of the isoflavone components produced intensely undesirable taste effects such as bitter, astringent and dry mouth feeling. Soybeans are known to contain the five isoflavone glycosides, genistin,^daidzin,1} glycitein 7-O-jS-D-glucoside (glycitin),2) 6"-O-acetylgenistin3) and 6"-(9-acetyldaidzin,4) and

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Saponins can be found in more than one hundred plant families and in some marine animals. However, chemical investigation of soybean (Glycine max L. Merrill) saponins has begun only as recently as the 1970s. Here we focus on the chemical structure, the content, and biological activity of soybean saponins in current studies. Especially, we focus on 2,3-dihydro-2,5-dihydroxy-6-methyl-4H-pyran-4-one (DDMP) conjugated saponins and define the chemical structure of this as a natural precursor of group B and E saponins.

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