Differentiation of market coffee and its infusions in view of their mineral composition

Abstract

The concentrations of 14 elements (Ca, Mg, K, Na, P, Co, Mn, Fe, Cr, Ni, Zn, Cu, Cd, Pb) were determined in market coffee samples after dry mineralisation of both dry samples and infusions evaporated to dryness. The total metal contents were analysed by flame atomic absorption spectrometry (F-AAS) using deuterium-background correction. Phosphorus was determined in the form of phosphomolybdate by spectrophotometric method. Reliability of the procedure was checked by the analysis of the certified reference materials Tea (NCS DC 73351), Cabbage (IAEA-359) and Spinach leaves (NIST-1570). It was concluded, based on RDA calculated for essential metals, that coffee infusions are not an important source of bioelements in human diet. In the case of toxic elements Provisional Tolerable Weekly Intake (PTWI) was estimated and there is no health hazard associated with exposure to Cd and Pb via coffee consumption. Significant correlation coefficients (p<0.001, p<0.01 and p<0.05) were found between concentrations of some metals in coffee. Factor analysis and canonical analysis were applied to the data processing in order to characterise the market coffee samples. The 12 metals determined were considered as chemical descriptors of each sample. Based on the mineral composition, it was possible to differentiate chemometrically particular types of coffee distinguishing arabica from robusta, ground from instant coffee, and their infusions.