Evaluation of thermodynamic properties and antioxidant activities of Achachairu (Garcinia humilis) peels under drying process

Abstract

AbstractThe aim of this study was to evaluate the effect of temperature on the drying kinetics of achachairu peels. Empirical and diffusive models were used to describe the drying kinetics and the thermodynamic properties of the process. Both fresh and dehydrated samples were characterized according to their bioactive compounds and antioxidant activity. The drying was carried out in an air circulation oven at a speed of 1.5 m s−1 at temperatures ranging from 40 to 80°C. Parameters of the effective diffusivity and activation energy were calculated considering the first six terms of Fick's model, and the thermodynamic properties are as follows: enthalpy, entropy and Gibbs free energy. Total phenolic compounds, antioxidant activity by ABTS•+ and DPPH•, and total tannins using aqueous and hydroalcoholic extracts were analysed for both fresh peels and the dehydrated. Page's model was considered to be the most appropriate for describing the drying process that occurred at a decreasing rate from the initial phases until the end of the process; Fick's model showed a higher diffusivity value at a temperature of 80°C. The activation energy of the process ranged from 27.773 to 27.569 kJ mol−1 depending on the number of terms used in Fick's model. The thermodynamic properties indicated that the process is endothermic and not spontaneous. The extraction process using solvents with different polarities (water and ethanol) enabled the extraction of phenolic compounds; however, the extraction by 'AE' revealed superior results for AA‐ABTS•+, TT and AA‐DPPH•, the latter not being capable of identifying differences in the fresh sample.