An Integrated Bioprocess Of Alcohol Fermentation And Aqueous Two-phase Extraction Of Steroidal Saponins From Dioscorea Zingiberensis

Dioscorea zingiberensis C. H. Wright (DZW) is an important plant resource to produce diosgenin which is the precursor of steroidal hormone drugs. Its tuber contains not only steroidal saponins of 1.1-16.5%but also starch of 40-50%and lignocelluse of 40-50%. Acid hydrolysis is traditionally used to produce diosgenin by directly mixing the DZW tuber and acid, in which the starch and cellulose are wasted and a great pollution exists to environment. Aiming at solving the problem of recource waste and environmental pollution, this dissertation focuses on the research of the saccharification and ethanol fermentation using the starch and cellulose in DZW and extraction of saponins using a novel aqueous two-phase system. The integrated process is simple and can achieve the goal of integrated utilization and clean production.First of all, the contents of starch and lignocellulose in the tuber of DZW were determined as follows:starch 38.7%, lignocellulose 40.9%, and cellulose 15.9%.The two hydrolysis methods (acid hydrolysis and two enzymes hydrolysis) were then inspected. The optimum conditions of acid hydrolysis are determined:the ratio of DZW and water of 1:4, the concentration of H2SO4 of 1.2%, the soak condition about 20h, hydrolyzing at 130℃for 50min. Under these conditions, the concentration of glucose achieves 89g/L and the content of saponins doesn't change much meanwhile. On the other hand, two kinds of enzymes were used to hydrolyze DZW and get the same concentration of glucose as the acid hydrolysis.The simultaneous saccharification and fermentation (SSF) was performed and optimized in the shake bottles. The experimental result showed that the hydrolyzed DZW can directly be used as the fermentation medium without addition of N resource. The optimal initial pH is 5.0 in culture medium. The optimal time for adding cellulase is 12h. The optimal adding amount of cellulase is more than or equal to 120 and 100 U/g DZW for acid hydrolysis and two enzymes hydrolysis, respectively. The concentration of ethanol is 39.2 and 39.5 g/L, respectively, in the fermentation broths. So the two-kind enzymes method is chosen for the starch hydrolisis.The SSF experiment was studied further in a fermentator. The optimal conditions of the adding time and amount of cellulase are 16h and 100 U/g DZW respectively. The transformation rate from cellulose to ethanol is 33.9%, which is 59.8%of the theoretical value.Finally, the microwave-assisted extraction of saponin from the fermentation broth was investigated using an aqueous two-phase system of ethanol-(NH4)2SO4, which shares the same result as one without microwave-assisted. While using DZW as material to extract saponins, the microwave-assisted extraction ratio is 25.9%higher than one without microwave-assisted. And the extraction rate of saponins from fermentation broth is 17.6%higher than that from DZW and there are more saponins with less sugar ligand in fermentation broths than that in DZW.