Quality changes in oil of walnut (Juglans regia L.) during storage

Abstract

The purpose of investigation was to appreciate the changes in quality of walnut oil obtained by cold pressing of kernels. The kinetics of chemical reactions of oil oxidation was studied. The accumulation of the primary and secondary compounds of oxidation process depending on the storage life was analyzed. The oil quality is subjected to permanent changes predominantly in the direction of nutritional quality losses. It has been established that the chemical and biochemical reactions of the oxidation of polyunsaturated fatty acids in the triglyceride structure are irreversible and consecutive. At the same time, it has been determined that during oil storage the reaction of primary compounds (hydroperoxides) formation by oxidation is of zero order, but the reaction rate is variable. At the initial stage of storage (20-21 days) the increasing of reaction rate constant (K, days-1 ) of hydroperoxides formation from K3=0.042days-1 at t=3°C to K60=1.82days-1 at t=60°C has been detected. The activation energy of the reactions was equal to 52.1kj/mol. However, the acidity index of oil increased in limited diapason from 0.12mgKOH/g to 0.19mgKOH/g.