Estudo cinético e termodinâmico da degradação térmica do arroz vermelho hidratado mediante método não isotérmico.

Abstract

The objective of this research was to investigate the decomposition kinetics of starch present in red rice in husk submitted to the hydration process at temperatures of 45°C, 55°C, 65°C and 75°C by means of thermogravimetric analysis and its derivatives (TG and DTG).The g-function (α) was obtained for the kinetic mechanisms of the Coats - Redfern (CR) model named one-dimensional contraction (R1 model), one-dimensional diffusion (D1 model), random nucleation and growth ( A2 model), random nucleation and growth ( A3 model) and random nucleation with two nuclei in the individual particle first-order mechanism (F1 model). The thermodynamic properties: enthalpy, entropy and Gibbs free energy were also determined. The results obtained reveal that the starch decomposition kinetics evaluated for hydrated red paddy rice occurred mass loss corresponding to 53.74% up to 57.07%, in the starch thermal decomposition temperature range in the second thermal event. In order to understand the energy associated with heat and mass transfer 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, while the Gibbs free energy increased with increasing temperature, and its values were positive, which characterizes a non-spontaneous process. Where it was made the calculation of the function g (α) showed that the first-order kinetic model (F1 model) fitted well to the experimental data, with a coefficient of determination greater than 99%, thus confirming that the mechanism that described the decomposition of starch present in hydrated red rice is first-order (n=1).