Studies On Extraction, Purification And Biological Activity Of Soybean Isoflavones In Soybean Whey

The technology of recovering soybean isoflavones from soybean whey,the waste water, in processing soy protein isolate in industry,was studied in order to give some scientific message for the comprehensive utilization and find out a new method to produce soybean isoflavones.Through ultrafiltration .extraction by ethyl acetate and column chromatography, the product in which the purity of soybean isoflavones was 72.45%,was obtained.The antioxygenic activity and antimicrobial activity of soybean isoflavones were examined.The extract from soybean whey was identified by color reaction, ultraviolet spectrum and high performance liquid chromatography(HPLC). Soybean isoflavones contained in the soybean whey was 7.12 g/mL by HPLC.Genistin and daidzin were the major components in the soybean isoflavones,and the ratio of the two components was nearly 1 : 1.The isoflavones aglycones in the soybean whey were not found by HPLC.Before ultrafiltration,soybean whey was pre-processed to remove proteins.Soybean whey protein was precipitated by adding metal salt into the soybean whey and heating it.According to the orthogonal design of two factors and three levels,the optimum pre-processing conditions was obtained as follows: CaCl2 added 5% based on the content of the solid substance in the soybean, pH adjusted 4.5,temperature 85 and time heated 15 minutes.In the case of these pre-processing conditions,the rate of protein precipitated was 49.8%,and the rate of soybean isoflavones retained was 90.4%.In experiments of one-factor design, appropriate ultrafiltration conditions were obtained.The ultrafiltration memberane made from poly(ether sulfone),whose molecular weight cut-off (MWCO)was 10000, was used.The ultrafiltration pressure was 34 ~ 51kPa,and the ultrafiltration temperature was 30~40 .Under these conditions, the rejection rate of protein was 83.9%,and the rejection rate of soybean isoflavones was 8.6%.When soybean isoflavones were purified by column chromatography.appropriate conditions were obtained.D4006 macroporous resin was chosen as adsorbent. The sample was added to the resin at the flow of ImL/min at 25 ,and the concentration of the soybean isoflavones in the sample were Img/mL.The adding volume was 2.67 liters per liter resin.At first,the resin was eluted by distilled water at room temperature to remove the aqueous impurities,and then the soybean isoflavones were eluted using gradient aqueous alcohol. According to the orthogonal experiment of two factors and three levels,we obtained the optimum eluting conditions as follows.The temperature was 75 ,and the flow was 1mL/min.Using alpha deoxyribose oxidation and pyrogallol autoxidation, experiments of soybean isoflavones scavenging hydroxy radical and superoxide radical were respectively made.In theABSTRACTappropriate concentration range.soybean isoflavones showed ability to scavenge hydroxy radical and superoxide radical,and soybean isoflavones showed antioxygenic activity.By filter paper method,the antimicrobial effect of soybean isoflavones was experimented-Soybean isoflavones showed antimicrobial activity to Escherichia coli,Staphylococcus aureus and Saccharomyces cerevisiae.The antimicrobial activity depended on the concentration of the soybean isoflavones. The soybean isoflavones had no antimicrobial activity to Aspergillus niger.