Method Validation for Multi-Elemental Analysis of Dialyzable and Non-dialyzable Fractions of Coffee Brews by F AAS and ICP OES: a Bioaccessibility Study

Abstract

A simple and fast, non-digestion treatment, and fully validated preparation procedures of dialyzable and non-dialyzable fractions of brews of ground (GCs) and instant (ICs) coffees prior to their elemental analysis (Al, Ba, Ca, Cr, Cu, Fe, Mg, Mn, Ni, Sr, and Zn) by flame atomic absorption spectrometry (F AAS) and inductively coupled plasma optical emission spectrometry (ICP OES) was developed. Three different procedures: wet digestions (P1), direct analysis (P2), and acidification with HNO3 (P3) were tested. Among tested procedures, the direct analysis (P2) gave the most satisfactory results, i.e., precision from 0.54% (Fe) to 5.9% (Cu), recoveries ranging between 98.0% (Sr) and 104% (Al), detection limits within 0.095 (Ba)–1.8 (Ni) μg L−1, and quantification limits from 0.32 (Ba) to 6.0 (Ni) μg L−1. The chosen procedure was applied to determine bioaccessibility of 11 elements in GCs and ICs coffees using in vitro gastrointestinal digestion. Average contributions of the bioaccessible fraction (%) of elements in brews were as follows: Al (19.0, 23.0), Ba (42.8, 48.4), Ca (35.0, 38.9), Cr (< LOD, 31.1), Cu (15.0, 14.3), Fe (5.08, 2.81), Mg (32.2, 37.9), Mn (28.1, 29.1), Ni (40.9, 60.0), Sr (43.2, 45.6), and Zn (11.5, 9.57) for GCs and ICs coffees, respectively. Generally, bioaccessibility of most elements, i.e., Al, Ba, Ca, Cu, Mg, Mn, Ni, and Sr in brews of GCs was lower than this determined in ICs and varied from 4% (Mn) to 47% (Ni). In contrast, higher contributions of the bioaccessible fraction of Fe and Zn were assessed for GCs brews (47% and 17%, respectively), than these evaluated in ICs brews. Additionally, results on total concentrations of elements in brews of GCs and ICs and concentrations of elements in the dialyzable fraction separated from these brews were applicable to differentiate and classify all analyzed coffees by principal component analysis (PCA).