Biological Purification And Transformation Of Functional Components In Soybean Molasses

Soybean molasses is a by-product of the production of soybean protein,with an annual output of about 100,000 tons.Soybean molasses contains abundant soybean oligosaccharides and soybean isoflavones.But,due to the viscous nature,soybean molasses are difficult to handle,and are usually used as low-cost animal feed or directly discharged as waste.In recent years,with the increasing attention to the utilization of by-products in soybean processing,there have been many reports on the extraction and isolation of soybean oligosaccharides and soybean isoflavones from soybean molasses.However,the research on the high-value utilization of soybean molasses by biological technology in China is still need to be further studied.Raffinose and stachyose,which are main functional oligosaccharides in soybean molasses with a total content of 20%,can maintain a healthy balance of intestinal flora as probiotics.In this study,microbiological purification was used for the enrichment of functional oligosaccharides in soybean molasses,and a strain of maltose yeast was screened out from yeasts,because it could effectively remove sucrose,glucose and fructose from soybean molasses,but effectively retained raffinose and stachyose.The optimal fermentation conditions of the selected strain in the enrichment of raffinose and stachyose were determined as:the soybean molasses were diluted 4 times,the maltose yeast was inoculated at the volume concentration of 6%,and the fermentation time was set as 24 h.Under this condition,The retention rates in soybean molasses were 21.93%for sucrose,85.02%for stachyose and 95.50%for raffinose.Soybean isoflavone aglycones are the key functional components of soybean isoflavones,and the hydrolysis of soybean isoflavone glycosides by ?-glucosidase is an effective method to prepare soybean isoflavone aglycones.In this study,4 P-glucosidase genes of TpBgl3,X74163,Bg13321 and Bg15391 were obtained by gene mining technique,heterologous expressed in E.coli BL21,and the enzymatic properties of the recombinant enzymes were also analyzed.It was found that the recombinant?-glucosidase TpBgl3 had an excellent enzymatic propertity with the specific activity of 98.78 U/mg.Its optimal temperature and pH were 85?and 4.0,respectively,metal ions of Mn2+and Ca2+ had a strong activation effect on its enzyme activity.In view of the characteristics of non-pathogenicity and strong protein secretion in the expression system of B.subtilis,TpBgl3 was further expressed in B.subtilis WB600.Compared with in E.coli BL21,the enzymatic properties of recombinant TpBgl3 did not change in B.subtilis WB600,while the expression was increased by 20.4 times.The TpBgl3 expressed in B.subtilis was applied to hydrolyze soybean isoflavones in soybean molasses,and the reaction conditions were optimized.It was found that the hydrolysis rates of daidzein,glycitin and genistein in the soybean molasses diluted for 4-folds were up to 100%,100%and 99.6%,respectively,under the ?-glucosidase amount of 0.4 U/mL and the hydrolysis time of 2 h.The result showed that TpBg13 had great application potential in the hydrolysis of soybean isoflavone glycosides.In this study,through the fermentation by maltose yeast and the hydrolysis by?-glucosidase,the green technology of biological purification and transformation in soybean molasses was built,bring a significant enrichment of functional oligosaccharides and isoflavone aglycones.The research improved the biomedical application value of soy molasses and was of great significance to the high-value utilization of soybean molasses.