Quantification of isoflavones by capillary zone electrophoresis in soybean seeds: effects of variety and environment.

Soybean isoflavones (genistin, daidzin, glycitin, and their malonyl forms and aglucons) are thought to be responsible for the astringent taste of soyfoods. Generally, HPLC with a methanol and water elution gradient is used for isoflavone quantification, but capillary zone electrophoresis (CZE) has been used more recently to separate several flavonoids in plant extracts. We present the results of CZE analysis of isoflavones in soybean extracts. Conditions for separation by using CZE were optimized for analysis of soybean isoflavones. We compared the results of extraction at different temperatures and with different compositions of solvent. Total extraction of isoflavones was not affected by temperature but was affected by composition of the solvent. Malonyl forms of isoflavones were thermally unstable. We analyzed the isoflavone content of different varieties of soybean seeds sown on different dates. Total isoflavone content varied among different varieties and with sowing dates. Interactions between the variety and the sowing date also affected isoflavone composition. We conclude that the variety of soybean seed and environmental growing conditions, such as sowing date, can contribute to seed quality by reducing its isoflavone content, modifying its isoflavone composition, or both.