The effect of fixed and rotary roasting methods on the oxidative stability of pistachio oil

Abstract

Today, the demand for vegetable oils has increased. Unsaturated fatty acids in pistachio oil are an important component in promoting the health of the human diet. The purpose of this study was to evaluate the oxidative properties of roasted pistachio oil in two fixed and rotary roasters at 160 °C for 15 min during 0, 3, and 6 months of storage. The heat used has led to the destruction of the oil in the roasted pistachios, and with the increase in the storage time, the peroxide value of the samples increased from 0.06 to 0.57 meq/kg in the fixed method and from 0.03 to 0.07 meq/kg in the rotating method, respectively. Free fatty acids and acid value increased from 0.34 to 1.34 % and 0.69 to 2.68 mg KOH/g in the fixed method and from 0.3 to 1.11 % and 0.6 to 2.20 mg KOH/g in the rotating method as a result of storage time for 6 months and lipolysis reactions. Under the effect of roasting heat, the Maillard reaction products played an important role in the thermal stability of the oil (P<0.05). The roasted samples at zero storage time have the highest inhibitory percentage of DPPH and the lowest IC50 (3.66 % in the fixed method and 6.9 % in the rotary method). In spite of the fact that the changes made during 6 months of storage in both roasting methods are within the standard range, but due to the fact that in the samples of roasted pistachios in the fixed method, the peroxide value increased and the oxidative stability decreased significantly, it is suggested to use the rotary method in roasting of pistachios.