Trace mineral content of Argentinean raw propolis by neutron activation analysis (NAA): Assessment of geographical provenance by chemometrics

Multielement analysis of raw propolis samples, collected from different central Argentinean regions, was carried out by Neutron Activation Analysis (NAA) aiming at developing a reliable method in their traceability. This work presents a characterization of 96 raw propolis samples selected from three different geographical origins in middle region of Argentina. Multivariate chemometric techniques, such as Principal Component Analysis (PCA), were applied to perform a preliminary study of the data structure. Two supervised pattern recognition procedures including stepwise linear discriminant analysis (LDA) and K-nearest neighbors (kNN) were used to classify samples into the three categories considered on the basis of the chemical data. Eight trace elements (Br, Co, Cr, Fe, Rb, Sb, Sm and Zn) were selected by stepwise-LDA explaining the classification of propolis according to their geographical origin. Application of k-nearest neighbor classification procedure to these eight selected variables produced a good correlation (98% correct classification ratio) of propolis with its provenance. The trace element profiles provided sufficient information to develop classification rules for propolis identification according to their provenance.