Determination of soyasaponins in Fagioli di Sarconi beans (Phaseolus vulgaris L.) by LC-ESI-FTICR-MS and evaluation of their hypoglycemic activity

Soyasaponins are oleanene-type triterpenoid saponins, naturally occurring in many edible plants that have attracted a great deal of attention for their role in preventing chronic diseases. The aim of this study was to establish the distribution and the content of soyasaponins in 21 ecotypes of Fagioli di Sarconi beans (Phaseolus vulgaris, Leguminosae). High-performance reversed-phase liquid chromatography (RPLC) with positive electrospray ionization (ESI(+)) and Fourier transform ion cyclotron resonance (FTICR) mass spectrometry (MS) in conjunction with infrared multiphoton dissociation (IRMPD) was applied for the unambiguous identification of soyasaponins Ba (m/z 959.5213, [C48H79O19](+)), Bb (m/z 943.5273, [C48H79O18](+)), Bd (m/z 957.5122, [C48H77O19](+)), and Be (m/z 941.5166, [C48H77O18](+)), which are the only commercially available reference standards. In addition, the several diagnostic product ions generated by IRMPD in the ICR-MS cell allowed us the putative identification of soyasaponins Bb' (m/z 797.4680, [C42H69O14](+)), alpha g (m/z 1085.5544, [C54H85O22](+)), beta g (m/z 1069.5600, [C54H85O21](+)), and gamma g (m/z 923.5009, [C48H75O17](+)), establishing thus their membership in the soyasaponin group. Quantitative and semiquantitative analysis of identified soyasaponins were also performed by RPLC-ESI(+) FTICR-MS; the total concentration levels were found ranging from 83.6 +/- 9.3 to 767 +/- 37 mg/kg. In vitro hypoglycemic outcomes of four soyasaponin standards were evaluated; significant inhibitory activities were obtained with IC50 values ranging from 1.5 +/- 0.1 to 2.3 +/- 0.2 mu g/mL and 12.0 +/- 1.1 to 29.4 +/- 1.4 mu g/mL for alpha-glucosidase and alpha-amylase, respectively. This study represents the first detailed investigation on the antidiabetic activity of bioactive constituents found in Fagioli di Sarconi beans.