Effect of roasting and microwave pre-treatments of pistachios on the yield and the quality of the extracted oil

Nowadays, there is a growing demand for the consumption of cold pressed oils. To overcome this problem, new thermal pre-treatments of seeds before pressing have been used. Microwave pretreatment is a modern method that has been presented to obtain high-quality oils with higher oil yield. In the present study, the effect of pre-treatments of pistachio nuts by roasting and microwaving prior to oil extraction by pressing, on the efficiency as well as the quality of the oil was investigated. Pistachio samples were treated with microwave oven (2450 MHz frequency) for 60, 120 and 180 seconds and for oven-pretreatment three levels of temperature (120, 150, and 180°C) for 15 minutes was applied. Also, in order to obtain the real amount of the pistachio oil yield, untreated samples were extracted by solvent. Hot pressing was performed at three temperature levels of 60, 80 and 100°C, to compare with the other thermal pretreatments. All the oil samples were then analyzed for their yield and the quality properties. According to the obtained results microwave and oven pretreatments increased the oil yield and oxidative stability as well as chlorophyll content of the oil. The results showed a decrease in oil acidity of the microwave-pretreated for 180 sec. however, different pretreatment methods had no significant effect (p<0.01) on carotenoid content of the pistachio oil. Totally, microwave pretreatment is an appropriate process before cold pressing of pistachio nuts, which improves the yield and quality properties and oxidative stability of pistachios oil.