Microwave-assisted extraction coupled to acid hydrolysis and biphasic separation for simultaneous production and recovery of diosgenin from Dioscorea nipponica Makino by HPLC analysis and activity validation

To obtaining diosgenin from Dioscorea nipponica Makino ( D. nipponica ) was usually subjected to the multiple processes such as extraction, hydrolysis, transformation and separation etc. In this study, a novel method for rapid production and recovery of diosgenin from D. nipponica was developed by integrating microwave-assisted extraction (MAE), microwave-assisted hydrolysis (MAH) and two-phase extraction (TPE) in one-step procedure, that named MAEH-TPE. Using a two-phase system of ethanol aqueous solution-sulfuric acid-petroleum ether, the MAEH-TPE process was optimized by single-factor experiments and response surface methodology (RSM). Under optimum conditions of ethanol aqueous solution of 60 % (v/v), sulfuric acid concentration of 1.4 mol/L, liquid-to-material ratio of 20 mL/g, extraction temperature of 90 ℃, and extraction time of 35 min, the yield of diosgenin reached 17.09 ± 0.32 mg/g which conformed very closely to the predicted value of 17.185 mg/g, and validation experiments confirmed effectiveness and reliability of the RSM model. Compared with the conventional methods, MAEH-TPE exhibited higher extraction yield, shorter extraction time and simpler operation. The mechanism in MAEH-TPE process was explored in detail by chromatographic analysis and multi-phase equilibria. Enzyme inhibition assay demonstrated that the inhibition rate of the extracted diosgenin on porcine pancreatic lipase (PPL) reached 56.18 ± 1.38 % with IC 50 of 191.42 µg/mL, further proving that diosgenin as the main parent structure of the saponins in D. nipponica dominantly contributed to PPL inhibitory effect. Also, the results proved that MAEH-TPE had excellent extraction performance and simplified the complex processes, reducing energy consumption and saving solvents and resources.