Distinctive carbohydrate profiles of black ginseng revealed by IM-MS combined with PMP labeling and multivariate data analysis

Abstract

Despite the widely recognized importance of ginseng carbohydrates, their structural analysis is still challenging due to structural complexity. This study presents the first ion mobility-mass spectrometry (IM-MS) combined with 1-phenyl-3-methyl-5-pyrazolone (PMP) labeling and multivariate data analysis for profiling carbohydrates in the seven ginseng products. 11 carbohydrates were tentatively annotated, including 5 first found in ginseng, and three of them were solely detected in black ginseng (BG) samples, speculated as monosaccharides bearing various groups based on MS² analysis. Furthermore, 3D profiles of carbohydrates in IM-MS of the samples showed good discrimination between the varieties of ginseng which were classified into two groups utilizing carbohydrate contents by PLS-DA. The big difference between BG and the others may be ascribed to the repeated heating and steaming process for preparation of BG products. Our findings may provide insights into the differences in bioactivity of different ginseng varieties for future research and show a valuable methodology for discovering unknown carbohydrates.

Keywords: 3D profiles; Carbohydrates; Ginseng; Ion mobility-mass spectrometry; Multivariate data analysis.

Graphical abstract

Fig. 1

The arrival time distributions (ATDs) of protonated or sodiated PMP derivatives of (A) RD, (B) DG, (C) FG, (D) AG, (E) BCFG, (F) BNSDFG, and (G) BCAG. The insets show enlarged graphs at relative low intensities. The bottom graph in each figure demonstrate the relevant 3D map, where the level of variation between light and dark represents the intensity of an ion. The ATDs are from three individual measurements, and deviation is ± 0.01 ms.

Fig. 2

The overall mobility spectra of the standard references of (A) fructose, (B) glucose, (C) maltose, (D) maltotriose, (E) maltotetraose, (F) isomaltotetraose, (G) laminaribiose, (H) mannose, (I) gentiobiose, (G) cellobiose, (K) isomaltose, (L) lactose, (M) sophorose, (N) isomaltotriose, (O) manninotriose, and (P) mannotetrose. The protonated disaccharide, trisaccharide, and tetrasccharide ions are shown by the ions at m/z 673.27, 857.33, 997.37 and sodiated ions at m/z 695.25, 857.30, 1019.35, respectively. The ions at m/z 511.23 and 510.23 are assigned as protonated glucose and fructose, respectively. The ion at m/z 532.20 corresponds to sodiated glucose. The ATDs were from three individual measurements, and deviation is ± 0.01 ms.

Fig. 3

(A–E) IM-MS/MS spectra of the ions at m/z 383.16, 385.14, 391.19, 421.20, and 420.21, respectively. The detailed information of product ions are shown in the right-hand panels. (F) The supposed molecular formula of the unknown carbohydrates. MW: molecular weight.

Fig. 4

The 3D representation of the IMS-MS data obtained on (A) RG, (B) DG, (C) FG, (D) AG, (E) BCFG, (F) BNSDFG, and (G) BCAG samples. Selected t_D range 0–10 ms, selected m/z range 200–1200.

Fig. 5

(A) PLS-DA score plot based on the carbohydrate abundances in the IM-MS spectra of the seven ginseng varieties (R²X (cum) = 0.84, R²Y (cum) = 0.984, Q² (cum) = 0.979). (B) Histograms of the top seven carbohydrates in VIP values. (C) Peak areas of the carbohydrates with VIP > 1 in the seven ginseng varieties. ***P < 0.001; *P < 0.05, n = 10.