Determination of optimal acid hydrolysis time of soybean isoflavones using drying oven and microwave assisted methods

The aim of the present research was to determine an optimal acid hydrolysis condition using drying oven and microwave assisted methods to estimate isoflavone contents by RP-HPLC in soybean. All isoflavone glucosides were completely converted to their aglycones at 120 min for drying oven and 50 min for microwave. Optimal extraction time of the highest isoflavone aglycone content after acid hydrolysis was achieved in 3 h. These results indicated that the optimised hydrolysis and extraction conditions of isoflavones in soybean were: soybean (1 g) hydrolysed by 10 ml of 1 N HCl at 100 °C for 50 min using microwave assisted acid hydrolysis method, and then 15 ml of EtOH was added to the mixture which leaved alone for 3 h at room temperature for complete extraction. Thus, microwave is an easy, consumed less time, and reliable acid hydrolysis method to estimate soybean isoflavones in comparison with drying oven method.