Rapid quantification of isoflavones in traditional Chinese soybean food by ultra-high performance liquid chromatography coupling to the UV detector

An efficient and rapid quantitative method was developed for the evaluation of six types of isoflavones in soy food, including daidzin, glycitin, genistin, daidzein, glycitein and genistein. An UPLC column, BEH C18(2.1 mm×50 mm, 1.7 μm)was employed with acetonitrile and 0.1% acidic H₂O(v/v)as mobile phase. The gradient was from 10% acetonitrile to 45% acetonitrile during 10 min at a flow rate of 0.3 mL/min. The detection wavelength was selected as 260 nm and the column was operated at 45℃. Six standard isoflavones were separated in 7.5 min and good linear relationships were achieved with correlation coefficients of 0.9998~0.9999. The recovery values in spiked samples were in the range of 96.8%~102.0%.The method was applied in the detection of isoflavones in traditional Chinese soyfood, including bean curd stick, dried toufu, bean curd shin, braised deep-fied bean curd, soft tofu, firm tofu and lactone bean curd. 8.67~25.83 g/kg isofavones was detected in the tested soyfood, and up to 88.0%~93.4% of isoflavones components were daidzin and genistin. These results suggested that isoflavones could be rapidly determined by ultra-high performance liquid chromatography coupled with photo-diode array detector in traditional Chinese soy food.