The 2012 ASHS Annual Conference

Edamame (Glycine max L. Merrill) is specialty-cultivars of vegetable-soybean selected for flavor, large seed size, and green seed yield.  Consumption in the United States has increased largely due to their nutritional value and purported health benefits. Soybean isoflavone concentrations change with seed development, but few studies have evaluated edamame, which often has fewer isoflavones than agronomic type beans.  The purpose of this study was to determine when isoflavones accumulate in six edamame cultivars.  Edamame cultivars from Wannamaker Seed Company [Midori Giant (MG), Mojo Green (MOJO), and Sunrise (SR)] and Rupp Seed Company [BeSweet 292 (BS292), BeSweet 2015 (BS2015), and BeSweet 2001 (BS2001)] were harvested semi-weekly between 69 and 97 days after planting (DAP) for a total of nine harvests.  The beans were frozen, lyophilized, ground and a 0.5 gram sample was extracted overnight with 12 mL of solvent consisting of 0.1 n hydrochloric acid, acetonitrile, and deionized water (2:7:3, v/v/v).  Soybean isoflavone and standard profiles for genistin, daidzin, glycitin, malonyl genistin, daidzein, glycitein, and genistein were performed on an Agilent 1200 series HPLC.  Total isoflavone concentration peaked for MG, MOJO, and BS292 between 88 and 90 DAP and at 90 to 95 DAP for SR, BS2015 and BS2001.  Total isoflavone accumulation is predominated by malonyl genistin, which at its greatest and least composed 76.4% and 50.8% of total isoflavones in BS2011 and SR at 97 DAP.  For all isoflavone species, at 69 DAP BS2015 and MOJO had the lowest and highest concentrations, respectively, which is likely due to differences in cultivar maturation time.  Daidzein, glycitein, genistein, daidzin, and glycitin concentrations ranged from 0.38 to 1.63, 0.02 to 0.5, 0.090 to 0.69, 0.12 to 0.81, and 0.15 to 0.83 µg/bean at 69 DAP, respectively.  Genistin and malonyl genistin were not detected among cultivars at 69 DAP.  Daidzin, glycitin, and genistin accumulated maximally between 88 and 95 DAP.  At 97 DAP, there were cultivar differences in only daidzin concentration, which ranged from 3.4 to 16.4 µg/bean for BS2015 and MG.  There were no differences between cultivars for the remaining isoflavones at 97 DAP with isoflavone concentration averages (µg/bean) for glycitin (4.2), genistin (4.8), malonyl genistin (55.5), daidzein (1.2), glycitein (3.2), genistein (1.8), and total (81.5). Although isoflavones are desirable, edamame quality characteristics such as texture and flavor would be reduced if harvest is delayed beyond 90 DAP (average harvest for cultivars) for isoflavone accumulation.  Of isoflavones measured, malonyl genistein and glucosides predominate.