UHPLC-PDA-ESI/HRMSn profiling method to identify and quantify oligomeric proanthocyanidins in plant products

Abstract

Oligomeric proanthocyanidins were successfully identified by UHPLC-PDA-HRMS(n) in a selection of plant-derived materials (jujube fruit, Fuji apple, fruit pericarps of litchi and mangosteen, dark chocolate, and grape seed and cranberry extracts). The identities of 247 proanthocyanidins were theoretically predicted by computing high-accuracy masses based on the degree of polymerization, flavan-3-ol components, and the number of A type linkages and galloyls. MS(n) fragments allowed characterization on flavan-3-ol based on the monomer, connectivity, and location of A-type bonds. Identification of doubly or triply charged ions of 50 PAs was made on the basis of theoretical calculations. A single catechin standard and molar relative response factors (MRRFs) were used to quantify the well-separated PAs. The ratios of the SIM peak counts were used to quantify each of the unseparated isomers. This is the first report of direct determination of each of the proanthocyanidins in plant-derived foods and proanthocyanidins containing an epifisetinidol unit in grape seeds.

Keywords: UHPLC-PDA-ESI/HRMSn profiling method; identification; oligomeric proanthocyanidins; plant products; quantification.

Figure 1

Structures of flavan-3-ol units and common fragmentation patterns for proanthocyanidins.

Figure 2

MS² spectrum of the EF–EC dimer with retention time at 26.98 min.

Figure 3

Accurate ¹²C and ¹³C isotope ion peaks for [M – 2H]^2– of m/z 720 and 1152 and for [M – 3H]^3– of m/z 960.

Figure 4

PDA (at 278 nm) and SIM chromatograms of grape seed extract.