Estudo das propriedades físico-químicas de diferentes tipos de cafés através de técnicas termoanalíticas e espectroscópicas

Abstract

The taste of coffee can be influenced by several factors such as the different temperatures used during the roasting process. When coffee is exposed to temperature variations, chemical and / or physical changes may occur in its structures and this may even contribute to the quality of the beverage. Because Brazil is the major producer and exporter of coffee in the world, it is necessary to develop effective methods of characterization that are capable of ascertaining the thermal and spectroscopic evolutionary behavior of this valuable national product. In general, thermoanalytical, spectroscopic and X-ray diffraction characterizations provide important information, such as thermal degradation, moisture and residue determination, vibrational analysis of the molecules of the material and allows a characterization of the crystalline structure of the samples. In order to evaluate the physicochemical properties of coffee samples thermogravimetry (TG), derivative thermogravimetry (DTG) and differential thermal analysis (DTA) were used, all of these analyzes were performed simultaneously with the analysis of gases evolved during the process of thermal degradation of the samples by Fourier transform infrared (FT-IR) spectroscopy. In addition, Raman spectroscopy and X-ray diffraction techniques were also used. The samples analyzed by these techniques were in nature and processed coffees, which were supplied by different producers of the Zona da Mata mineira. It was possible to observe through the TG technique the occurrence of mass loss of the samples in three stages. Also, a great similarity was observed between the DTA curves of in nature and roasted coffee. The analysis of the gases involved (EGA) by FT-IR revealed the release of H2O, CO2 and two unidentified gases. From Raman spectroscopy it has been found that the region between 1000 and 1800 cm -1 (-1) is dominated by bands characteristic of chlorogenic acid and the spectral range of 2800 to 3000 cm3 (-1) is attributed to lipid bands. In addition, it has been observed that the thermally treated samples have a lower amount of chlorogenic acid than the in nature coffee. By X-ray diffraction no crystalline structure was observed, concluding that the material is amorphous. Thus, based on the results obtained it is possible to suggest that the techniques used in this work are efficient tools with great potential to serve as comparative methods of coffee samples.