Oxidation kinetic studies of virgin and solvent extracted pistachio oil under Rancimat test conditions

Pistachio is one of the most popular nuts and a good source of oil. Four commercial varieties of pistachio oil using cold press and solvent extraction methods were obtained in the current study. The fatty acid profile and chemical properties were achieved via gas chromatography and chemical methods, respectively. This work aimed to investigate the oxidation kinetics of pistachio oil based on oil stability index (OSI) at high temperatures (110-150 degrees C) using rancimate and determine the effect of extraction methods and chemical properties on OSI. The results showed that the mean values of temperature coefficient (Tc), excitation factor (Q(10)), activation energy (Ea), frequency factor (A), and Gibbs free activation energy was - 2.97 degrees C, 1.98, 92.15kJ /mol, 59.12 x 10(10), and 103.09J/mol degrees k, respectively. Each unit change in Ea was associated with a mean change of 9.52 x 10(10) in A, indicating a greater contribution of factor A than Ea to the stability of pistachio oil. Ea and A correlated well with enthalpy ( increment H) and entropy ( increment S) values, respectively. OSI values were well described with Delta G(++) values so that the highest and the lowest ones were related to Ahmad Aghaei and Kaleghuchi virgin oil, respectively. The stability of pistachio oil is more affected by intrinsic antioxidants than the composition of fatty acids. The extraction methods indirectly affected the oxidative stability of pistachio oil due to the extraction of different amounts of antioxidant compounds.