Diosgenin production from Dioscorea zingiberensis tubers by novel pressurized hydrolysis in acidic ionic liquids

Diosgenin (25R-spirost-en-3β-ol; CAS No.: 512–04–9), a plant-derived natural product, has significant importance for manufacturing steroid-based drugs. It is primarily prepared by direct acid hydrolysis, but this out-of-date process is not environmentally friendly. In recent decades, ionic liquids have shown good potential to replace conventional organic solvents in many fields. The aim of this study was to develop a novel approach for diosgenin production, in which the acidic ionic liquid [BHSO₃MIm]HSO₄ was employed under pressurised conditions to hydrolyse the crude saponin of Dioscorea zingiberensis C. H. Wright tubers for the first time. The hydrolysis conditions were optimised through a one-factor-at-a-time experiment, and the maximum yield of diosgenin was achieved at 3.71 ± 0.18 % with an ionic liquid concentration of 0.5 M, a solid–liquid ratio of 1:30 g/mL, a hydrolysis temperature of 140°C, and a hydrolysis duration of 0.5 h. The diosgenin yield was 75.67 % of the maximum yield after six consecutive applications of [BHSO₃MIm]HSO₄. The yield achieved was comparable to pressurised acid hydrolysis and microwave-assisted ionic liquid hydrolysis and significantly higher than that of direct acid hydrolysis (P<0.01). Meanwhile, catalyst consumption was 0.123 mol/g diosgenin, which was much lower than that of microwave-assisted ionic liquid hydrolysis (0.600 mol/g). Moreover, the hydrolysis reaction was completed within 0.5 h, which was only one-third of the conventional pressurized acid hydrolysis. This newly established method has significant merit in hydrolysis duration and is associated with decreased catalyst consumption, and [BHSO₃MIm]HSO₄ is of good reusability, making it a greener and more economical method for diosgenin preparation.