Structural characterization of major soyasaponins in traditional cultivars of Fagioli di Sarconi beans investigated by high-resolution tandem mass spectrometry

• Published in: Analytical and bioanalytical chemistry Vol. 407; no. 21; pp. 6381 - 6389
• Main Authors: Bianco, Giuliana, Buchicchio, Alessandro, Cataldi, Tommaso R. I
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-08-2015; Springer; Springer Nature B.V
• Subjects: Analytical Chemistry; Beans; Biochemistry; Carbohydrate Conformation; Carbon dioxide; Carbon dioxide lasers; Characterization and Evaluation of Materials; Chemical properties; Chemical structure; Chemistry; Chemistry and Materials Science; Chromatography; Common beans; Cultivars; dissociation; ecotypes; European Union; Food Science; Fourier transforms; Fragmentation; gases; High-Resolution Mass Spectrometry in Food and Environmental Analysis; Identification and classification; Infrared; Ionization; ions; Irradiation; Laboratory Medicine; Legumes; Liquid chromatography; Mass spectrometry; Methods; Monitoring/Environmental Analysis; Observations; Phaseolus - chemistry; Phaseolus vulgaris; Physiological aspects; protected designation of origin; Research Paper; reversed-phase high performance liquid chromatography; reversed-phase liquid chromatography; Saponins; Saponins - chemistry; Scientific imaging; Soyasaponin; spectrometers; Structural analysis; sugars; tandem mass spectrometry; Tandem Mass Spectrometry - methods; wavelengths; Italy; MED, Italy; Italy, Basilicata; Soyasaponins I; Mass accuracy; Group B soyasaponins; βg; Infrared multiphoton dissociation; V; αg; Mass spectrometry; Ion cyclotron resonance
• ISSN: 1618-2642; 1618-2650
• DOI: 10.1007/s00216-015-8810-3

Major soyasaponins, i.e., soyasaponins I, V, βg, and αg from traditional Fagioli di Sarconi beans (Phaseolus vulgaris L., ecotype Tabacchino), were analyzed by reversed-phase liquid chromatography–mass spectrometry (MS) using high-resolution Fourier transform ion cyclotron resonance (FTICR) MS on electrospray ionization in positive-ion mode. Fagioli di Sarconi beans are protected by the European Union [Commission Regulation (EC) No 1263/96] with the mark PGI (for “Protected Geographical Indication”), and are cultivated in Basilicata (southern Italy). Protonated adducts of soyasaponins I, V, βg, and αg were observed at m/z 943.5262, 959.5213, 1069.5583, and 1085.5534, respectively. Gas-phase dissociation of soyasaponins by infrared multiphoton dissociation FTICR MS was performed using a CO₂ laser source at a wavelength of 10.6 μm. Most of the fragment ions were identified unambiguously by using the high-resolution and accurate mass value provided by the FTICR mass spectrometer. All soyasaponins exhibit a sequential and neutral loss of sugar moieties at relatively short irradiation times (i.e., less than 50 ms). When the pulse length was increased, a more pronounced fragmentation occurred, with several signals in the lower part of the mass spectrum. In the case of soyasaponins βg and αg, the occurrence of the conjugated product ion at m/z 127.0389 ([C₆H₆O₃ + H]⁺, 2,3-dihydro-2,5-dihydroxy-6-methyl-4H-pyran-4-one) was evidenced. Coupling reversed-phase liquid chromatography with high-performance FTICR MS in combination with infrared multiphoton dissociation tandem MS proved to be very promising for the structural characterization of soyasaponins, and is also suitable for the rapid and accurate structural investigation of other saponins.