Effect of the roasting process on glass transition and phase transition of Colombian Arabic coffee beans

Abstract

This paper presents results of the analysis of organic coffee beans cultivated in Departamento del Cauca -Colombia. Beans studied are of the Coffea Arabica species cultivated in mountain soils of altitude close to 1500 m. Samples from green and roasted beans were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and X-ray diffractometry (XRD). We intend to relate the features of the heating spectra with the transformation experimented by the coffee. Glass transition and phase transitions were examined. DSC and TGA spectra show that the green coffee experiments a high and fast decomposition after 200°C until 289°C with a remarkable transformation in a close range around 210°C. XRD shows significant changes for green and roasted beans associated to the amount of caffeine hydrates and caffeine anhydrous. Fit of XRD curves by Lorentzian shows a considerable increase of the active crystalline phase at 2θ equal to 20.4 0 for the roasted coffee. The results obtained from this study contribute to the insight associated with the final quality of coffee dependent on roasting methods. Better quality of coffee requires a refined and very controlled roasting process around of 218°C with a slow thermal treatment since the room temperature until the 200°C.

Chemical, Functional, and Structural Properties of Spent Coffee Grounds and Coffee Silverskin

“…According to some authors, the thermal treatment by which the coffee beans are subjected could be responsible for at least a part of the crystallinity observed in SCG structure since this process promotes the elimination of some water molecules incorporated into the crystal fraction, transforming some α-polymorph to β-crystal phase structures (Rivera et al 2011).…”

Initial Roasting Temperature Effect on Thermal Behaviour and Characteristic of Liberica Coffee

“…The decrease in the roasting temperature is caused by the process of heat transfer from heat sources to coffee beans that occurred in the beginning roasting process associated with the drying process and is characterized by a decrease in the mass of coffee (EDZUAN et al, 2015). The mass of coffee beans decreased by 20 % from its initial mass due to an endothermic process of melting (RIVERA et al, 2011), dehydration, thermal degradation of carbohydrates, and the pyrolytic reaction of minor compound (BRONDI et al, 2017). After the 15 min, the coffee beans of spectroscopic analysis with FTIR for fractional group of chemical (BALLESTEROS et al, 2014), decomposition material by using X-ray powder diffractions (XRD) (RIVERA et al, 2011) and the type of elements with Scanning Electron Microscope (SEM), chemicals identification by LC-MS.…”

“…The mass of coffee beans decreased by 20 % from its initial mass due to an endothermic process of melting (RIVERA et al, 2011), dehydration, thermal degradation of carbohydrates, and the pyrolytic reaction of minor compound (BRONDI et al, 2017). After the 15 min, the coffee beans of spectroscopic analysis with FTIR for fractional group of chemical (BALLESTEROS et al, 2014), decomposition material by using X-ray powder diffractions (XRD) (RIVERA et al, 2011) and the type of elements with Scanning Electron Microscope (SEM), chemicals identification by LC-MS. There have been limited investigations of Liberica coffee beans, although knowledge of its thermal changes and chemical characterizations of Liberica coffee beans may be of importance to compare the characteristic of varied coffee beans.…”

“…The phase change from amorphous to crystalline is due to the roasting process. Thermal treatment of coffee causes incorporated water molecules into its crystal structure (RIVERA et al, 2011;PERDANA et al, 2018). The crystalline regions of cellulose are resistant to attack from various chemical compounds due to strong hydrogen interactions between micron fibres.…”

“…The roasting process causes improve profile thermal behavior, characterization thermal behavior by Differential Scanning Calorimeter (DSC) and spectroscopic method to drive of reactions lead to Maillard reactions and formation of melanoidins (MRP-Ms), that has been already studied in roasted coffee beans (FARAH;DONANGELO, 2006). The DSC spectra of the green coffee experiments show a high and fast decomposition after 200 °C until 289 °C with a remarkable transformation in a close range around 210 °C (RIVERA et al, 2011). The roasting process also causes a very significant increase of a crystalline phase of the caffeine with activity at 2θ equal to 20.4° when the coffee is roasted.…”