Saponins in Ipomoea batatas tubers: Isolation, characterization, quantification and antioxidant properties

Triterpene saponins are a class of plant natural products with a wide range of bioactivities, which makes them an interesting research subject. This work reports, for the first time, the isolation and characterization of saponins in Ipomoea batatas tuber flour, their quantification and antioxidant properties. Their structures were characterized on the basis of UV, FAB-MS, ESI-MS, GC-MS, polarimetry and NMR data, as: oleanolic acid-3-O-[.beta.--glucopyranosyl-(12)-.beta.--galactopyranosyl-(12)-.beta.--glucuronopyranosyl]-28-O-.beta.--glucopyranoside (sandrosaponin IX) (1) and oleanolic acid-3-O-[.beta.--galactopyranosyl-(13)-.beta.--glucuronopyranosyl]-28-O-.beta.--glucopyranoside (2). A new quant. HPLC-DAD method for saponin content detn. in this tuber was developed and validated. Their total content was 200.01 mg/100 g dry wt. (RSD = 7.2%; p < 0.001). The single saponin contents were: 161.20 mg/100 g dry wt. (RSD = 0.58%; p < 0.001) for saponin 1 and 14.67 mg/100 g dry wt. (RSD = 0.41%; p < 0.001) for saponin 2. The antioxidant activities, tested by DPPH and FRAP assay, of total phytochem. fraction and of single saponins were moderate in relation to com. stds.