Recognition of spectral identifier from green coffee beans of arabica and robusta varieties using laser-induced breakdown spectroscopy

Coffee is one of the world's commodity that is cultivated in more than 50 countries. Production of coffee in Indonesia is positioned of fourth rank in the world, after Brazil, Vietnam, and Colombia. There are two varieties of coffee grown in Indonesia, i.e. the arabica and robusta. The chemical compositions between arabica and robusta are different each other. A trained coffee tester can distinguish these differences from its taste, but it is very subjective. Laser-Induced Breakdown Spectroscopy (LIBS) is a spectroscopic technique based on the analysis of micro-plasma induced on the surface sample after being shot with a laser pulse. In this study, elemental spectra acquired using Laser-Induced Breakdown Spectroscopy (LIBS) technique were analysed to differentate between green coffee beans of arabica and robusta, which are collected from plantations in Malang, Bondowoso, Prigen, and Pasuruan. Results show that optimum conditions for acquiring spectra from green coffee beans using LIBS are at 120 mJ of laser energy and 1,0 μs of delay time. Green coffee beans of arabica and robusta contain some elements such as Ca, W, Sr, Mg, Be, Na, H, N, K, Rb, and O. Discriminant analysis method was then applied to distinguish the green beans of arabica and robusta coffee. Element identifiers of green coffee beans are Ca, W, Mg, Be, Na, and Sr. The abundant element in green coffee beans is Calcium (Ca), and depth-profile testing shows that Ca is homogeneous inside the beans.