Determination of steroidal saponins in different organs of yam (Dioscorea pseudojaponica Yamamoto)

Yams (Dioscorea spp.) are perennial trailing rhizome plants. Steroidal saponins, furostanol and spirostanol glycosides are the marked functional compounds in yams. In this investigation, a C18 solid phase extraction method was developed for yam saponins purification. The contents of saponins in various organs of yam (Dioscorea pseudojaponica Yamamoto) were also determined. Results showed that the recoveries of yam saponins extracted by the developed method were about 99.48-100.08% when the saponins (each saponin weighed 0.20, 0.50 and 1.00 mg) passing through the C18 cartridge. The extractive method could efficiently reduce the interferences from impurities in yam saponin extracts prior to HPLC analysis. The recoveries of added saponins in different yam organs were 98.34-99.92% for tuber flesh, 95.98-98.89% for tuber cortex, 97.89-99.44% for rhizophor, 93.82-98.01% for leaf and 93.87-97.65% for vine, respectively. The yam tuber cortex had the highest amount of saponins (582.53 μg/g dw), which was higher than that existed in the tuber flesh (227.86 μg/g dw) about 2.55 times. The contents of saponins in the rhizophor, leaf and vine of yam were 29.39, 24.41 and 23.96 μg/g dw, respectively.