For the data analysis, principal component analysis (PCA) was carried out on the SNV- and MSC-processed spectra from both FTNIR and FT-IR. PCA can readily be applied to spectroscopic data to perceive the nature and scattering level of the data. The first principal component (PC1) describes the maximum of variation or spread in the samples. A second principal component (PC2), orthogonal to the first (i.e., completely uncorrelated), describes the maximum of the variation not described by the first eigenvector, and so on. With this procedure, the most important features of the data set can be seen in a low-dimensionality plot.19 A multivariate calibration model of a partial least-squares regression (PLSR) was then developed using all of the preprocessed spectral data to predict the extent of adulteration in the pure onion and adulterated onion powder samples. PLSR is particularly suited when the matrix of predictors has more variables than observations, such as from spectral data. PLSR has been used in food authentication studies based in spectroscopic data.11 Multivariate analysis was performed using MATLAB software version 7.0.4 (The Mathworks, Natick, MA, USA).