FTIR spectroscopy and multivariate analysis for differentiating Allium and Eleutherine species as spices and medicinal plants

Allium cepa, A. ascalonicum, and Eleutherine bulbosa are used as spices, seasonings, and traditional medicines. These three species are frequently frauded because they are morphologically similar in shape and color. The confusion is even ampler when they are provided as dried powder. Metabolomics fingerprinting and chemometrics were used to detect sample adulteration quickly. The metabolite fingerprinting using Fourier-transform infrared spectroscopy (FTIR) was conducted at various sample ranges and concentrations. FTIR data were analyzed by unsupervised (PCA) and supervised (PLS and OPLS) techniques. Data analysis was performed at different wavenumber ranges, 4000–400 cm^–1, 4000–2800 cm^–1, and 1800–400 cm^–1. The results showed that the three samples could be identified using FTIR spectral fingerprints, which revealed similarities between A. cepa and A. ascalonicum, and both are different from E. bulbosa. The chromatogram profiles of the three samples exhibited differences in the groups of S = O (sulfonyl chloride), S = O (sulfoxide), and C–Br (R–Br). The PCA, PLS-DA, sPLS-DA, and OPLS-DA models used in pure and mixed samples demonstrated a high percentage of differentiation by both internal and external validation, indicating that they represent suitable methods to meet the purposes of this study.