Catalytic alcoholysis of saponins in D. zingiberensis C. H. Wright (Curcuma longa L) with magnetic solid acid to prepare diosgenin by response surface methodology

•A magnetic solid acid was prepared and can be recycled.•A alcoholysis method was used to extract diosgenin from saponins.•The parameters for the alcoholysis were optimized by Response Surface Methodology.•The yield of diosgenin obtained in this work is higher than traditional method.