Chemical analysis and classification of black pepper ( Piper nigrum L. ) based on their country of origin using mass spectrometric methods and chemometrics

The current study applied gas chromatography-mass spectrometry (GC-MS), liquid chromatography-mass spectrometry (LC-MS), and thermal desorption direct analysis in real-time mass spectrometry (TD-DART-MS) methods to the analysis of black pepper (Piper nigrum L.) samples from different countries. The black pepper powder samples were analyzed directly by TD-DART-MS without any extraction, but for GC-MS and LC-MS methods, a methanol extraction procedure was employed before the analysis. Various compounds, such as piperamides and terpenes, were detected. Partial least squares-discriminant analysis (PLS-DA) was used to classify black pepper samples based on their origins. Total ion mass spectrum (TMS) data profiles from GC-MS, LC-MS, and TD-DART-MS methods were constructed and evaluated for the performance of classification. A cubicroot data transformation was tested in the data preprocessing and found to be effective for improving the classification rates. The average classification rates of PLS-DA models with GC-MS-cubic-root-TMS, LC-MS-cubicroot-TMS, and DART-MS-cubic-root-TMS data representations were 94.1 +/- 0.6%, 87.7 +/- 0.6%, and 97.0 +/- 0.3% respectively, for 100-time bootstrapped-Latin-partition cross-validation. This study presents for the first time the analysis of plant-based food materials by using TD-DART-MS, and it has been demonstrated as a simple and highthroughput method for classification studies.