Two sample preparation methods for the determination of minerals from green coffee were investigated for the purpose of methodological evaluation: ashing and acid digestion. The concentrations of minerals Al, Ba, Ca, Co, Cu, Fe, K, Mg, Mn, Ni, P and Zn were evaluated by the technique of Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). The mineral contents in green coffee did not differ significantly at the level of 5% (it Tests F) for both methodologies used. The accuracy of ashing and acid digestion were evaluated, respectively: Al = 93% and 104%; Ba = 85% and 54%; Ca = 99% and 108%; Co = 98% and 96%; Cu= 78% and 96%; Fe = 96% and 96%; K = 91% and 82%; Mg = 100% and 95%; Mn = 104% and 101%; Ni = 95% and 107%; P = 101% and 104%; Zn = 89% and 96%. The ashing methodology was used for the determination of minerals amounts from 45 samples of green coffee from the growing regions of São Paulo, Minas Gerais and Bahia states. The levels of minerals obtained in mg kg-1 by ash digestion were: Al (0.612 to 32.2), Ba (1.11 to 17.6), Ca (925 to 1889), Co (0 to 1.16), Cu (6.21 to 369), Fe (23.3 to 367), K (12252 to 17205), Mg (1526 to 2059), Mn (14.2 to 60.4), Ni (0 to 44.2), P (1172 to 1826) and Zn (3.71 to 57.0). The employment of the instrumental technique of ICP-OES and digestion of the sample for ashes were shown to be appropriate for the simultaneous determination of mineral elements in coffee since the levels of precision and accuracy proved to be satisfactory.
green coffee; minerals; determination; ICP-OES
