Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/5/2006
Publication Date: 12/7/2006
Citation: Kim, S., Berhow, M.A., Kim, J., Chi, H., Chung, I. 2006. Evaluation of soyasaponin, isoflavone, protein, lipid, and free sugar accumulation in developing soybean seeds. Journal of Agricultural and Food Chemistry 54:10003-10010. Interpretive Summary: Soybeans are a source of a number of key nutritional compounds including proteins, carbohydrates and lipids, as well as a number of nutriceutically important compounds including isoflavones and saponins. However, the levels of these compounds in mature seeds vary from cultivar to cultivar and from growing location and season. This work evaluates the ratio of isoflavones and saponins to total lipids, proteins and sugars in two Korean soy cultivars and show that the ratio of isoflavones to all other components generally increases as the seed matures, while that of the saponins generally decreases as the seed matures. Relatively little information is available on isoflavone and soyasaponin concentrations and their interaction in developing soybean seeds. This study focuses on the changes of isoflavone and soyasaponin concentration during seed development and their relationship to the other major chemical components, such as protein, lipids and free sugars.
Technical Abstract: A combination of analytical techniques were used to examine and quantify seed compositional components (protein content, lipid content, carbohydrates, isoflavones, and saponins) during bean development and maturation in two Korean soy cultivars. Protein accumulation was rapid during reproductive stages, while lipid content was only relatively moderately increased. The major carbohydrate saccarides, sucrose and stachyose, constantly increased during the reproductive stage. Previously published results suggest that the free sugar and lipid content reached their maximal concentrations at a relatively early stage of seed development, and remain constant in comparison to other chemical components. The malonylglucosides were the predominant isoflavone form followed by the glucoside, acetyl glucoside and aglycone forms. Soyasaponin concentration was relatively low until the R8 stage. Soyasaponin BetaG was the major soyasaponin in DDMP-conjugated group B soyasaponins, followed by the non-DDMP counterpart, soyasaponin I and soyasaponin A1. The ratio of total isoflavone to total soyasaponin in the developing soybean increased from 0.06 to 1.17. Protein, lipid and free sugar contents in the developing soybean seeds showed significant positive correlations with conjugated isoflavones and total isoflavone concentration, while the lipid contents showed a negative correlation with the isoflavone aglycone. Protein, lipid and free sugar contents showed a negative correlation with total group A and B soyasaponins and total soyasaponins; however, only the soyasaponin A content was significantly negatively correlated with free sugar content. Total soyasaponin content was negatively correlated with isoflavone content (r=-0.828 at p < 0.01).