Environment-friendly Extraction Of Diosgenin From Dioscorea Zingiberensis Rhizome

Diosgenin from Dioscorea zingiberensis is an important medicinal material. Diosgenin is extracted from D. zingiberensis rhizome by acid hydrolysis which produces massive acidic waste water. In order to develop an environment-friendly process to extract diosgenin from D. zingiberensis rhizome, experiments were conducted in biological way and chemical way, respectively. Biotransformation of dioscin into diosgenin was studied by special microorganism screening and fermentation. Automatic chemical processs were studied to develop a high efficient extraction of diosgenin from D. zingiberensis rhizome. The results are as follows:1. Based on the screening culture media with dioscin sugar(DL) as the only carbon source, a special microorganism species was obtained and identified as Penicillium dioscorea. Activation culture media of P. dioscorea were optimized as follows: MS without sugar and agar(1000ml) + 8.0 g DL /8.0 dioscin, culture temperature 30℃, culture time 36 h. The D. zingiberensis rhizoms were cut into pieces and fermented with the liquid spawn. The optimized fermentation conditions were as follows: 0.05 g mycelia /1kg rhizome,fermentation temperature 30℃, fermentation time 48 h,and the yield of diosgenin was 93%.2. Extraction of diosgenin from dioscin by acid hydrolysis with simultaneous extraction of diosgenin, without production of acid waste awter. Firstly, dioscin was extracted from dried rhizome. Then a reaction system was established with the dioscin powders, 1.0M sulphuric acid and petroleum ether in the ratio of 25kg:50L:100L. The reaction conditions were optimized as: temperature 95℃,200 r/min, reaction time 1h. After the hydrolysis reaction completed, the petroleum ether was recycled to obtain diosgenin. While the waste water which contained sulphuric acid was used for the next hydrolysis. So in this whole process, there was no acid waste water produced.3. Reverse chromatography of diosgenin is proved to be a high efficient purification process for industrial use.By the traditional crystallization method, the extracted diosgenin could be purified to be over 95%, with melting point at 192℃. However, this purification process was of high cost and low efficiency. In this paper, a reverse chromatography purification method was developed and a kind of purification equipment was designed. Diosgenin powders were put into the chromatography column, and then petroleum ether was heated at 80℃ to produce vapor and pressure. The pressure pushed the vapor to go up through the diosgenin powders, and then diosgenin and impurities which were pushed to the upper. In this transferring process, diosgenin crystallized while the impurities were transfer to the upper and crystallize at the surface. With this purification method, diosgenin could be purified to be over 95%, with melting point over 192℃. This reverse chromatography proved to be of high efficiency and low cost, and could be used in purification industry.In conclusion, biotransformation of dioscin into diosgenin needs further study for industrial utilization, while the acid hydrolysis of dioscin could be scientifically optimized to avoid the production of acid waste water. Acid hydrolysis with simultaneous extraction of diosgein successively produced no contaminants, and the revserse chromatograpgy significantly lowered purification cost.