Researchers in Tennessee reported results of seventeen cultivars grown at three locations. They found that the total isoflavone concentration ranged from 2,038 to 9,514 mug/g. They reported a moderate, or strong, negative correlation of total isoflavone with total seed oil, and five of the seventeen cultivars had a strong positive correlation with seed protein.
Charron, C.S. and co-workers. 2005. Correlations of oil and protein with isoflavone concentration in soybean (Glycine max (L.) Merr). J. Agric. and Food Chem. 53(18): 7128-7135.