Separation And Purification Of Soybean Isoflavones

This paper studied the separation and purification of soybean isoflavones from the extract of soybean. It included two main processes, separation of the isoflavones by column chromatography as well as crystallization, and hydrolysis of the isoflavones to change the glycosides to aglycones.Firstly, we separated the isoflavones from the soybean extract through column chromatography. The characteristics of static and dynamic adsorption as well as desorption of isoflavones on DS adsorbent were studied. The optimum conditions for static adsorption were as follows: water as solvent, temperature 40℃, pH 7.0-8.0. At the temperature 40℃, the saturated adsorption capacity of isoflavone was 150.6 mg·g^-1. The effect of temperature on the dynamic adsorption was the same as on the static adsorption. At temperature 50℃, flow-rate 2.5 mL·min^-1, initial concentration 7.03 mg·mL^-1 in water, the dynamic saturated adsorption capacity of isoflavone was 105.0 mg·g^-1. By studying the factors that affect the purities of products and recoveries of isoflavones, we got the optimum conditions for desorption: 70℃, eluting solvent sequence: water 3.0 BV, 75% ethanol 5.0 BV, flow-rate 2.5 mL·min^-1. Under these conditions, the content of isoflavones in the product was 56.0% with the recovery of 89.3%. The content of isoflavones in the product was ten times larger than in the initial material.Then we purified the product by crystallization to get a higher purity. The optimum conditions were: 70% ethanol as the solvent, the ratio of solvent to material between 15 and 20 (mL/g), crystallization temperature 4℃. A product of isoflavones with the content of 80% was obtained.To get the isoflavone aglycones, we hydrolyzed the above product which was mainly in the form of glycosides. The catalyst for the hydrolysis was a cationic resin, and the temperature of reaction was between 100℃ and 105℃, and the solvent was 75% ethanol.Through five cycles of hydrolysis, the glycosides were totally changed to aglycones.Then we vaporized the solvent and purified the isoflavone aglycones by extraction. A product of isoflavone aglycones with the content of 80% was obtained.