Estudo do processo de parboilização do Arroz vermelho cultivado no Sertão Paraibano.

Abstract

The application of the parboiling process will result in grains with differentiated characteristics when compared to conventional rice. The objective of this study was to evaluate the mathematical modeling of the drying process of the red rice submitted to the parboiling process in different autoclaving times and drying temperatures and to characterize the parboiled red rice, confirming the chemical, thermal, structural and morphological changes of the starch of biopolymers analyzed. To describe the behavior of drying kinetics, the Page and Midilli Model was used, with the Midilli Model being the best model. In order to evaluate the effects of water migration in the face of the studied phenomenon, the effective diffusion coefficient (Def) and the activation energy (Ea) were calculated. It was verified that the effective diffusivity in the grains increases with the elevation of the temperature of the drying air and, the longer the autoclave time in the same temperature, the slower the speed with which the water leaves the product. Activation energy, on the other hand, describes that the lower its value, the faster the water will be removed from the grains. In order to understand the energy associated with heat transfer and mass in the drying process, the thermodynamic properties (enthalpy (ΔH), entropy (ΔS) and Gibbs free energy (ΔG)) were determined. The enthalpy and entropy showed a tendency to decrease with increasing temperature, since the free energy of Gibbs increased with the increase of temperature, being its positive values, which characterizes a non-spontaneous process. In order to characterize the parboiled red rice starch, the following analyzes were performed: X-ray diffraction (XRD), Thermogravimetric Analysis (TG), Thermogram Derived Curve (DTG), Differential Exploratory Calorimetry (DSC), Vibrational Spectroscopy in the Region of Fourier Transform Infrared (FT-IR) and Scanning Electron Microscopy (SEM). The XRD confirmed the reduction of the crystallinity of the starch, the TG allowed the determination of the average initial temperature of degradation and the obtaining of the DTG provided the values in which the phenomenon of dehydration occurs and the degradation events. The DSC analysis confirms the thermal events, the FT-IR and the MEV recorded the modification in the chemical structure of the starch. Thus, any analyzed autoclave time modifies the starchy rice structure, as well as any drying temperature complete the parboiling process.