Influence of Temperature and Air Velocity on Drying Time and Quality Parameters of Pistachio (Pistacia vera L.)

Abstract

Drying is one of the important steps in pistachio processing. In this step kernel moisture content is decreased from 50 to less than 5% (d.b.) which will result in suitable condition for storage. Study of effective parameters in pistachio drying is important since these parameters influence drying time and kernel quality. In this research, a mono layer of pistachios was dried at three different temperatures (60, 75, and 90°C), and three levels of drying air velocity (1.5, 2, and 2.5 m/s). Changes of drying time, protein, fat and peroxide value were investigated for two common Iranian pistachio varieties Kalehghouchi and Fandoghi. Sensory tests were also used to check flavor of pistachios dried at the three temperature levels (60, 75, and 90°C). Statistical analysis of the data indicated that increasing the temperature to 90°C reduced drying time down by about 37% and caused a change in pistachio flavour. Taste tests indicated a consumer preference for pistachios dried at 75°C. If the air velocity is increased from 1.5 to 2.5 m/s, drying time reduces about 10 percent. Changes in temperature and air velocity have no significant effects on protein and fat content of pistachios, but if temperature reaches 90°C, peroxide value will increase to 0.55 meq/kg, which is still within the permissible limit for processed pistachios.