Color kinetics of longan flesh drying at high temperature

The aim of this study was to investigate the color kinetics during hot air drying of longan flesh at high temperatures. The longan of E-dor variety (Dimocarpus Longan Lour.) was used in this study. The sample sizes of 25-30 mm in diameter with the initial moisture content of 470–510% dry basis were tested. The experiments were carried out in the laboratory dryer at the drying air temperature of 60-130 °C. Kinetic parameters for the color change were determined using CIE system measuring L*, a* and b* values. These values were used to calculate the total color difference (ΔE), chroma and hue angle. The data of L*, a*, b* and ΔE were fitted to various kinetic models. It was found that the modified kinetic model (second order polynomial equation) provided the best fit of the data of L* and b*. The zero-order kinetic model was found to be the most suitable for describing the a* data and this model was found to be effective for representing the changes in ΔE values. Both models could predict the color change during drying relatively well. The simulated results showed that the drying air temperature and drying time affected the color change during the drying processes. The value of L* decreased when the drying time and temperature increased. The values of a*, b* and ΔE increased in the first period of drying afterwards these values decreased with drying time and drying air temperature.