Studies On β-Glucosidases Hydrolysis Of Soybean Isoflavone Glucosides

Soybean isoflavones contain many biological properties such as cancer-preventive property. Some reasearches found that the biological activities of isoflavone aglycones were much higher than that of isoflavone glucosides. 99% of total soybean isoflavones are isoflavone glucosides and normal processing of soybean cannot increase the content of aglycones, therefore it is significant to study the hydrolysis of isoflavone glucosides. In the present study, the hydrolytic capacities of soybean isoflavones of different b-glucosidases were studied.The objectives of this paper were to find the source of P -glucosidase with high activity and low cost to produce products with high isoflavone aglycones content.This is the first study on the extraction and characteristics of b-glucosidase from some Chinese soybean cultivar in the world. b-glucosidase from soybean (No.42 Dongnong ) can hydrolyze p-nitrophenyl-b-D-glucoside but not cellobiose. The optimal reaction conditions with p-nitrophenyl-b-D-glucoside occurred at 45 C with pH5.0. 77% of the activities remained after incubation at 50 C for 5 min. No differences were observed on the activities and thermostability of b-glucosidase from different soybean cultivar.Production of b-glucosidase by fermentation from Aspergillus niger was studied and 37 units of enzyme activity per milliliter culture obtained. The enzyme showed higher thermostability than that of soybean P -glucosidase for about 92% of the activities remained after incubation at 50 C for 2 hour. Meanwhile, the thermostability of purchased b -glucosidase from was also studied, and it demonstrated that the thermostability of b -glucosidase from Aspergillus niger was better than that of P -glucosidase from almond. When the enzyme was incubated at 40 C for 2 hour, the remaining activity was only 63% of the original level.Soybean isoflavone aglycones were analyzed by gas chromatogram(GC) and the GC assay method was established for the first time in China. The daidzein standard curve equation was Y=71519X-85913 with correlation coefficient R2 =0.9937. The standard deviation(SD) was lower than 7% when six samples were continuously analyzed.This is the first report to study the hydrolysis of soybean isoflavones glucosides with P -glucosidase from soybean, Aspergillus niger and almond. The optimal hydrolysis conditions and efficiency of each enzyme were established. Comparing with the hydrolysis efficiencies of acid hydrolysis, b-glucosidase from Aspergillus niger showed the highest hydrolysis efficiency.Products with high aglycones content were obtained using the optimal method ofhydrolysis(hydrolysis of isoflavone glucosides by b-glucosidase from Aspergillus niger). 72.9 milligram product with 12.6 milligram daidzein were obtained after hydrolysis of 360 milligram powder with 40% isoflavones glucoside by b-glucosidase Aspergillus niger.Master: Sun Yan-mei Major: Food Science Supervisor: Prof. Zhang Yongzhong...