Comparative Untargeted Metabolic Profiling of Different Parts of Citrus sinensis Fruits via Liquid Chromatography-Mass Spectrometry Coupled with Multivariate Data Analyses to Unravel Authenticity

Abstract

Differences between seven authentic samples of Citrus sinensis var. Valencia peel (albedo and flavedo) and juices from Spain and Uruguay, in addition to a concentrate obtained from Brazil, were investigated by untargeted metabolic profiling. Sixty-six metabolites were detected by nano-liquid chromatography coupled to a high-resolution electrospray-ionization quadrupole time-of-flight mass spectrometer (nLC-ESI-qTOF-MS) belonging to phenolic acids, coumarins, flavonoid glycosides, limonoids, terpenes, and fatty acids. Eleven metabolites were detected for the first time in Citrus sinensis and identified as citroside A, sinapic acid pentoside, apigenin-C-hexosyl-O-pentoside, chrysoeriol-C-hexoside, di-hexosyl-diosmetin, perilloside A, gingerol, ionone epoxide hydroxy-sphingenine, xanthomicrol, and coumaryl alcohol-O-hexoside. Some flavonoids were completely absent from the juice, while present most prominently in the Citrus peel, conveying more industrial and economic prospects to the latter. Multivariate data analyses clarified that the differences among orange parts overweighed the geographical source. PCA analysis of ESI-(-)-mode data revealed for hydroxylinoleic acid abundance in flavedo peel from Uruguay the most distant cluster from all others. The PCA analysis of ESI-(+)-mode data provided a clear segregation of the different Citrus sinensis parts primarily due to the large diversity of flavonoids and coumarins among the studied samples.

Keywords: albedo; concentrate; coumarins; flavedo; flavonoids; juice; metabolomics; orange.

Figure 1

Representative nLC-MS base peak chromatogram of orange parts extracted by methanol on negative ionization (A) albedo from Uruguay, (B) orange concentrate from Brazil, (C) flavedo from Uruguay and on positive ionization, and (D) juice from Uruguay. For peak numbers, refer to Table 2.

Figure 2

MS-based PCA of all orange samples (n = 3) negative ionization (A) score plot, (B) relevant loading plot and (C) HCA; positive ionization (D) score plot, (E) relevant loading plot and (F) HCA. AS: Albedo from Spain; AU: Albedo from Uruguay; CB: concentrate from Brazil; FS: Flavedo from Spain; FU: Flavedo from Uruguay; JS: Juice from Spain; JU: Juice from Uruguay.

Figure 3

MS-based OPLS of flavedo from Uruguay (FU) against all other samples negative ionization (A) score plot and (B) relevant loading S-plot; positive ionization (C) score plot and (D) relevant loading S-plot.