Effects of solar drying along with air recycling system on physicochemical and sensory properties of dehydrated pistachio nuts

Fresh pistachio was dehydrated with shade drying, sun drying, solar drying (without and with air recycling) systems (Methods I, II, III and IV). Then their impacts were studied on drying time, physical properties and also organoleptic criterions (shell appearance, color, roasted flavor, finger releasing kernel, sweetness, shell splitting and overall palatability) of dehydrated pistachio. The ambient-air temperature rise and drying time of pistachio in Methods I, II, III and IV reached to 1, 1, 14, & 17 °C; and 48, 19, 16, & 13 h, respectively. While the trends of drying rates in all methods were completely quadratic (R2 = 0.99), Method IV had the lowest shrinkage and the highest drying rate, shell splitting (70% more than Method I), bulk density and kernel density in comparison with other Methods. Whereas the pistachio's color properties (a, b and L), changed significantly when dried with Methods of I, II and III, the “L”, and “a” values of pistachio dried with Method IV had no significant difference with those dried with Method I (having the best color properties). The pistachio dried with Method IV (had the best sweetness and roasting flavor) in comparison with those dried with other methods because of higher drying rate.