Pistachio nut is an edible seed of pistachio (Pistacia vera L.) tree. Drying is an important operation in pistachio nut processing. The moisture content in nuts drops from 37-40 % (w.b.) to 5-6% during the drying process. A high quality to be obtained pistachio nuts depends on fast and efficient handling as well as drying operations. In this study, using a factorial completely randomized design, effect of drying air temperature at four levels(25, 40, 55 and 70°C), air velocity at three levels (0.5, 1.0 and 1.5 m/s) and relative humidity at two levels (5 and 20%) on chemical properties (peroxide value and free fatty acids), sensory attributes (shell appearance, split shell, firmness, sweetness, rancidity, roasted flavor and overall palatability), physical properties (broken nuts, loose nuts and split shell percent) and aflatoxin in pistachio nuts were studied. The results showed that drying air temparature was the most important factor in the process of drying of pistachio nuts. Higher drying air temparature resulted in shorter drying period. Effect of drying air temperature and air velocity were significant on some quality traits of pistachio nuts while the effect of relative humidity (within the studied range) was not significant. At higher drying air temperatures, free fatty acids as well as peroxide value in dried pistachio nuts increased. The effect of drying process on split shells in pistachio nuts was significant and increased with increase in drying air temperature. Aflatoxin content of pistachio nuts did not change during drying, indicating that drying process does not seriously affect aflatoxin content. Finally based on different quality traits, drying process was optimized.
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