Influence of Drying Temperature on Drying Kinetics and Appearance of Avocado Slices in Heat Pump Drying Process

The avocado is a nutritious fruit that originated from tropical countries such as Central and Southern America, and Southeast Asia. From the commercial point of view, it is an important fruit with a total world production is around eight million tons in 2020. Fresh avocados can be consumed directly or stored before advanced processing. The drying technique can be applied as an efficient post-harvesting technique to prolong the storage time of avocados. In this paper, heat pump drying experiments were performed to evaluate the influence of drying conditions on the drying time, the moisture diffusion coefficient, and the color change of avocado slices. It was obtained that color change can be decreased by increasing the drying temperature from 35 °C to 50 °C. Additionally, the effective moisture diffusivity was enhanced approximately two times by increasing temperature. It was suggested that a drying temperature of 50 °C should be used for the heat pump drying system operation and design to shorten drying time and prevented the quality of avocado. Additionally, empirical models were established to describe the drying behavior of avocados. The results indicated that the Page model can reflect well the evolution of moisture content over time with determination coefficient R2 greater than 0.996.