The Effect of Solar Drying Method in Air Recycle Mode Comparing with Traditional Method (Exposing to Direct Sunlight) on the Quality Properties of Pistachio Nut

Pistachio nut is one of the main Iranian non-oil exporting goods. Due to the importance of drying method to prevent of the quality properties of product from pistachio kernel and also utilizing renewable sources of energy, a solar dryer equipped with air recycle system was designed and fabricated, and its results were compared with traditional drying method (exposing to direct sunlight). Fresh Kalle-Ghuchi variety whole Pistachio was purchased daily from one of the gardens of Sabzevar County. To test the solar dryer, daily data recording was conducted from 9:00 AM to 15:00 PM. Some quality properties of dried pistachio such as shrinkage, moisture content, color indexes and sensory attribute were measured and evaluated. The results indicated that the solar drying method reduced the drying time by 31.57% compared to the traditional method. Investigation of quality properties showed that solar dried pistachio nut in air recycle mode had the lowest shrinkage, moisture content and color change. Also the results illustrated that the traditional method had the highest score in roasting index. Overall, according to Iran’s high potential of solar energy, using it for drying agriculture crops, especially pistachio nut, is recommended and emphasized.