Simultaneous Analysis of Free/Bound Phytosterols and Diosgenin in Taiwanese Yams

Gas chromatography (GC) and high performance liquid chromatography (HPLC) methods were developed for the simultaneous analysis of phytosterols and diosgenin in two representative Taiwanese yams, Dioscorea pseudojaponica Yamamoto and Dioscorea alata L. The major phytosterols found were β-sitosterol, stigmasterol, and campesterol. GC afforded good separation of phytosterols and diosgenin, with the diosgenin peak appearing between stigmasterol and β-sitosterol. For HPLC, UV detection had higher sensitivity (detection limits 0.03–0.09 μg); however, evaporative light scattering detection (ELSD) achieved higher noise tolerance and did not show baseline interference from solvent gradients. In addition, mixed solvents for extraction before acid hydrolysis, which is necessary to avoid fibers and acid hydrolysates binding to the target compounds, were evaluated. Phytosterol contents of 30.1 and 9.9 mg/100 g were found in D. pseudojaponica Yamamoto and D. alata L., respectively. Diosgenin was only found in D. pseudojaponica Yamamoto at a content of 15.2 mg/100 g.