Sun-infrared heating film drying analysis of Sultana seedless grapes: Operating modes

Abstract

In contrast to the technique of utilizing infrared heating films (IRHFs) as the main or auxiliary heating source in the dryer, this study investigated the quality and performance parameters of sun drying the Sultana seedless grapes (Vitis Vinifera L.) on IRHFs without using a dryer system. In this context, sun drying with four IRHF operating modes was analyzed: sun drying (Model-1), sun + daytime IRHF (Model-2), sun + 24 h IRHF (Model-3), and sun + night IRHF (Model-4). Model 1 used no electricity, whereas the other models consumed 7.21, 10.38, and 9.80 kWh of electricity. The average drying efficiency of all drying models varied between 5.25 % and 16.48 %. Considering all experiments, average De values changed from 4.2837E−07 to 5.443E−07 m2/s. The drying times were significantly shortened (2–3 times faster) in Models 2 and 3, and the color quality was highest in Model 4. Moreover, grapes dried using sun + IRFH gave the best results regarding physicochemical and bioactive quality properties such as pH, total phenol, total tannin, vitamin C, and total sugar compared to Model-1, which requires a long drying period. This study’s findings indicate that sun drying with IRHF, which shortens drying time and offers higher quality in terms of color and food content, may be an alternative method that can be adapted to the traditional sun drying method.