Isoflavone profile and antioxidant activity of Brazilian soybean varieties

Thirteen varieties and one new strain of soybean, developed by the Genetic Improvement Program from Empresa Brasileira de Pesquisa Agropecuaria (EMBRAPA), crop year of 2003, were analysed in relation to their isoflavones profiles and contents. Total isoflavone content varied from 57 to 188 mg per 100 g of soybeans. Most (90-95%) of the isoflavones were present as glycosilated derivatives. The beta-glycosides represented the main forms of the isoflavones in the seed (50 to 59% of the total) followed by malonylglycosides (28 to 39% of the total). The ratio between malonyldaidzin and daidzin varied from 0.44 (Embrapa soyseeds BRS 155) to 0.74 (BRS 185) and between malonylgenistin and genistin from 0.56 (BRS 155) to 0.87 (BRS 185). The total percentage of each isoflavone, corresponding to the sum of the four chemical forms (malonylglycoside, acetylglycoside, beta-glycoside and aglycone) varied from 39 to 57% for genistein, 34 to 47% for daidzein, and 8 to 17% of the total for glycitein. Antioxidant activity varied from 37.8 (BRS 214) to 48.9% (BRS 233) of inhibition of the beta-carotene bleaching, and a low correlation was found for antioxidant activity and total phenolics content or level and kind of isoflavones.