Drying characteristics and kinetics of colour change and degradation of phytocomponents and antioxidant activity during convective drying of deseeded Terminalia chebula fruit

Terminalia chebula Retizus fruit contains phytochemicals like phenols including flavonoids which are responsible for hypocholesterolaemic, anti-inflammatory, anti-allergic, antimicrobial, antioxidative properties. In the present study the effect of drying temperatures (40–80 °C) on drying kinetics during convective drying of deseeded T. chebula fruit was investigated. The data from the drying experiments were fitted into seven different drying models and the best model was selected by comparing the coefficient of determination (R2) and root mean square error (RMSE). Degradation kinetics for vitamin C, antioxidant activity (DPPH radical scavenging activity), total phenol content (TPC) and total flavonoid content (TFC) was evaluated at 60, 70 and 80 °C. Change in colour at these temperatures were also observed. From the results it was found that an increase in the temperature increased the drying rate and the drying time was reduced, and the mathematical model for drying which best fitted the experimental data was ‘Approximation of diffusion’ model. The degradation of the phytochemicals and change in colour followed the first order kinetics. The rate at which vitamin C degraded was found to be higher than the other components for all temperatures. The rate of change in total colour difference (ΔE*) decreased with increasing temperature.