Improving open sun and indirect solar drying kinetics with physicochemical quality of regal seedless grapes by novel pretreatment solution

Abstract

This paper reports a study of the physicochemical quality and the drying behavior of regal seedless grapes (RSG), pretreated with a novel solution (Olive oil: 2%, calcium carbonate: 2% and distilled water: 96%), then open sun-dried and dried in an indirect solar dryer. To show the effect of soaking time and temperature of the solution, two soaking times are carried out (120 and 240 s) at two temperatures (333.15 and 353.15 K). Quality indicat or such as shrinkage, color, rehydration capacity, titratable acidity, power of hydrogen (pH) and polyphenol content are evaluated. The results show that the time required to dry treated RSG varies from 220 to 328h during indirect solar drying (ISD) (during 428 h for untreated samples), and from 164 to 180 h during open sun drying (OSD) (during 290 h for untreated samples). The effective moisture diffusivity of solar-dried RSG ranges from 0.316 to 3.030 mm2s−1and that of open sun-dried regal seedless grape ranges from 0.706 to 5.700 mm2 s−1. Pretreatment affects the pH values significantly, whereas the rehydration capacity showes a large difference between the treated and untreated RSG. The solar-dried RSG has more stable color and ISD retains more of their polyphenol content.