Drying of Melons in a Solar Tunnel Dryer: The Effect of Ascorbic Acid Solution on Drying Kinetics and Color Parameters

Abstract

This study aims to present the performance of the solar tunnel dryer, which is required for the drying of two different types of melon with and without pretreatment. The solar tunnel dryer used in the study was built at Isparta University of Applied Sciences, Department of Agricultural Machinery and Technologies Engineering. The dryer consists of a flat plate solar collector, drying tunnel, solar cell module and a small axial fan. During the drying process, solar radiation, drying air temperature, relative humidity and air velocity were measured continuously in different parts of the dryer. At the same time, the mass loss of the melon slices was measured every two hours during the drying period. On the other hand, colour measurements were made on untreated and pre-treated melon slices, fresh and after drying, before and after the trials. Fresh melon samples were washed with tap water, and cut in half with a knife, the core in the middle was removed and sliced by hand in a half-moon shape without peeling before pre-treatment. 1% ascorbic acid was applied to the fruits as a pretreatment. After the preparations, the solar tunnel drying behaviour of untreated and pretreated sliced melon samples was investigated. Drying characteristic curves were evaluated according to five different mathematical models.  In this study, it was determined that the L*, a* and b* values of melon varieties were preserved without pretreatment. The lowest total color change was observed in the bleached samples in both types of melon samples.