The Study On Antioxidant Activity Of Isoflavone Extracted From Different Varieties Of Soybean And The Bean Sprouts

Soybean isoflavones are secondary metabolites in soybean which have manyphysiological activities, and called phytoestrogens. So many medical scientist andnutritionist have attention to isoflavone because of its antioxidant activity, anti-aging,prevention of cancer and other biological activity. Many studies have shown that soyis rich in isoflavones, so it’s challenge for us to use the rich variety of soybean in ourcountry. Soybeans, black beans and peas are selected for study by HPLC-MS(n)method. The following studies in this thesis have been done:1. The extraction condition such as solvents and extraction time have beenoptimized based on the content of isoflvone. Under this condition, we found the bestextraction condition are as following: extraction time is3h, extraction temperature is70℃, solid-liquid ratio is1:30and extraction solvent is ethanol/H2O=7:3.2. We studied the isoflavone of8soybean varieties by HPLC-MS(n)method,including soybeans, black beans and peas. In the study,15peaks were found and12compounds were identified. They are G, D, GL, MD, MG, MGL, AD, AG, De, Ge, Gleand an unknown component. G and MG take the highest content, the averageconcentration range from54.60mg/100g to89.34mg/100g and from57.04mg/100gto89.94mg/100g. The second highest level is MD. Overall, the soybean and smallblack bean have the highest content of isoflavone, and the small grain species havemuch more isoflavone than the large grain species (the isoflavone content of smallsoybeans are higher than the large soybean, as well as the small black beans).3. We studied the antioxidant activities of the isoflavone extract by DPPH andFRAP method. The studies showed that the small black bean have the highestantioxidant of DPPH and FRAP value, the tamba black beans take the second. Weanalysis the correlation of the isoflavone content and DPPH, FRAP. The analysisshowed that they have no significant correlation (R~2DPPH=0.328，R~2FRAP=0.227). Asour known, the black beans have anthocyanins which have strong antioxidant activity.And they showed significant correlation classified into two groups by black beans andnon-black beans. The result also showed that the correlation of antioxidant value andthe anthocyanin content is significantly higher than the correlation of antioxidantvalue and the isoflavone content.4. We also analysis the isoflavone of sprouts classified by different lengths. Thestudy found that the content of G in bean sprout is43.2%lower than the raw beans,but the content of MG is24.4%higher than the raw beans, the content of D is18.3%lower, the content of De, Ge and GLe are39.6%,82.7%, and10.8%higher than theraw beans, respectively. The percentage of G and D are significantly lower in beansprouts than that in raw soybeans; in contrast, the percentage of MD and MG are significantly higher; at the same time, the percentage of Ge, De and GLe have nosignificantly difference, about2~3%. The soybean sprouts have the highestisoflavone content when3cm long, regardless of analysis by dry weigh or wet weight.5. We analysis the isoflavone of the bud and the cotyledon by separate thesoybean sprout. The result by HPLC-MS analysis showed that the content of G in rawsoybean is56.09mg/100g, but the content down to35.52mg/100g and42.17mg/100gin the bud and cotyledon respectively; the content of MG have a slight increase, insharp contrast, the content have significantly decline in bud, from59.26mg/100downto6.30mg/100g; the content of D from23.44mg/100g down to15.97mg/100g whileup to87.42mg/100g; the content of GL and MGL in the raw soybean and cotyledon isvery low but high enough to106.07mg/100g and52.57mg/100g respectively.We separated the bud and the cotyledon when the sprouts are6cm long. After thestudy by HPLC-MS, we found that the components of cotyledon and raw beans aresimilar, in contrast, the components of bud is significantly different. The content ofGL, MGL are significantly higher than which in the raw beans and cotyledon; thecontent of D in cotyledon is lower, but the content is much higher in bud. At the sametime, we classified the isoflavone as following: the isoflavone beased on Ge, De andGLe respectively, analysis the percentage in all isoflavone, the result showed that thecomponents of isoflavone are similar between bean sprouts and raw beans, but thecontent of isoflavone based on GLe is much higher than which in the cotyledon andraw beans; the content of isoflavone based on Ge is much lower than which in thecotyledon and raw beans; the content of De, Ge and GLe have no significantlydifference.The isoflavone in bud (430.42mg/100g) is significantly higher than which incotyledon and raw soybean, about2.3times and2.55times each, calculated with dryweight; and also about2times than which in the cotyledon, almost80%highcompared with raw soybean. So the bud can provide rich isoflavone for us in dailydiet.