Applicability of ICP-OES, UV-VIS, and FT-IR Methods for the Analysis of Coffee Products

Abstract

Spectroscopic methods were applied to study and compare the nutrient composition of ground, instant, and chicory coffee products. The total concentrations of 17 elements, including major (Ca, Mg, P) and trace (As, Ba, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Se, Sr, Ti, Zn) elements were determined in solid samples and infusions from ground coffee by means of inductively coupled plasma atomic optical spectrometry (ICP-OES). For measurement of As and Se levels, hydride generation technique (HG-ICP-OES) was used. The accuracy of the element measurements was verified by the analysis of certified reference materials (tea leaves (INCT-TL-1), apple leaves (1515), and TORT-2). Caffeine was determined by UV spectrometry. Infrared spectroscopy was applied to investigate organic matter of the coffees. Soluble oxalate was determined by a redox titration. Additionally, measurements of some physico-chemical parameters such as moisture, ash, pH, and starch (coffee adulteration) were performed. Differences in the composition of analyzed ground and instant coffees based on the contents of caffeine, oxalate, and minerals such as Cu, Mg, P, and Zn were found. FT-IR spectroscopy was a suitable tool to characterize the presence of caffeine and oxalate.

Keywords:

• Caffeine
• Coffee products
• FT-IR
• ICP-OES
• Minerals
• Soluble oxalate
• UV-Vis

Acknowledgments

The work was financed by a statutory activity subsidy from the Polish Ministry of Science and Higher Education for the Faculty of Chemistry Wroclaw University of Technology.

Notes

I atomic line, II ionic line.

^a not detected.

^a Vega-Carrillo et al. (2002).

^b Martin et al. (1999).

^c Anderson and Smith (2002).

^d Zaidi et al. (2006).

^e Grembecka et al. (2007).

^f M. Oliveira et al. (2012).

^g Santos and de Oliveira (2001).

^a −negative effect; +positive effect.

^b whole bean.

^c freshly ground.