Heat Treated Soybean And The Transformation Of Soy Isoflavones Aglycone And The Determination Of Reducing Power

Soy isoflavones are a class of secondary metabolites, which were known as phytoestrogens for the similar structure with endogenous estradiol. Epidemiological studies shows that soy isoflavones were thought to have many beneficial health effects in humans, including chemoprevention in hormone-dependent cancers, for example, breast and prostate cancers. Additionally, they were used to relieve menopausal symptoms and reduce the incidence of cardiovascular disease and osteoporosis. Soy isoflavones, in short, have received considerable attention recent years due to the functions above-mentioned.Soy isoflavones belong to a group of compounds named flavonoids which shared a basic structure consisting of two benzene rings linked through a heterocyclic pyrone ring. They are a class of nonsteroidal estrogens that bear similarity in chemical structure and properties to estrogens. Of all the phytochemicals present in soybeans, isoflavones are present in significant high amounts. Soybeans contain 1-2 mg of total isoflavones/g, with large variation due to environmental factors. The 12 main isoflavones found in soybeans are daidzein (De), glycitein (Gle) and genistein (Ge) and their respective malonyl, acetyl and glucosyl forms. Aglycone forms which had the content no more than 2%-3% were the active composition as they could be absorbed directly. Glucosides, on the other hand, were thought to be less active, until they were hydrolysed to aglycones by enzyme. Changes of isoflavone distributions in soy were dependent on the processing conditions, such as heating, fermentation, frying, toasting, baking and acid condition. These processes converted malonyl-glucosides into corresponding aglycones andβ-glucosides.The inoxidizability and reducibility could be determined by some texts, such as free radicals remove experiments, ORAC, FRAP, and reduction experiment of potassium ferricyanide. The results were not the same as each other.Objective:The aim is analyzing the conversion of aglycones by heat treated, providing a reference to raw material selection and the manufacturing process for the health products of soy isoflavones, and guiding people how to consume soy products reasonable. In addition, to establish a method for evaluate the reducing capacity of soy isoflavones. the experimental condition of ultrasonic extraction, were optimized detailed. The samples were separated by high performance liquid chromatography and aglycones andβ-glycosides were detected by ultraviolet-visible detector, after they were treated with oven-drying, microwave heating and stir frying. And then calculate the contents and the ratio of isoflavone aglycones, analyze the effect on the conversion by heating.The absorbance value of solutions had a linear correlation with the content of reducing materials within a certain range in the phenanthroline reduction test and potassium ferricyanide reduction test. Evaluate the reducing power of sample by detecting the absorbance value, with ascorbic acid as a reference substance.Results:The content of aglycones increased gradually when the oven-drying temperature rose from 50℃to 150℃, whileβ-glycosides had no significant change. The contents ofβ-glycosides and aglycones increased the most in the stir fryed soybean. The result of microwave heating was the same as oven-drying at 50℃. Three group unknown Chromatographic peak area were reduced or disappeared. The correlation coefficient of regression equation of six standard solution is greater than 0.999, the RSD was less than 5.1%, and average recovery was between 87.5% and 110.0%, the RSD of recovery was 8.4%.The reduction tests showed that the order of 6 soy isoflavones reducing power is:genistein, daidzein, glycitein, daidzin, glycitin and genistin.Conclusion:The formation of aglycones and glucosides of isoflavones from malonyl derivatives was increased during the heating process, especially stir-fry, which could promote the transformation of aglycones, and improve the bioavailability of soybean isoflavones, enhance its nutritional value and health care. The content of soy isoflavones were more increased in soy products. The contents and the ratio of soy isoflavones were different for the varieties.Glycitein could be extracted in bean and bean sprout.The reducing capacity of samples was related with the content of total isoflavones.