Determination of the oxidati̇ve stabilty of cold pressed apricot and plum kernel oils

In the cold pressed plum (Prunus domestica) and apricot(Prunus armeniaca) kernel oils, various chemical properties as regards free acidity, peroxide value, specific extinction coefficients (K232 and K270) and fatty acid composition were determined as the initial analyses. Free fatty acid, peroxide value, K232 and K270 values for (in) the plum and apricot kernal oils were detected to be 1.54% and 1.56%, 4.87 and 2.42 meq O2/kg, 1.93and 1.86, 2.09 and 0.41, respectively. In the plum and apricot kernel oils with abundant unsaturated fatty acids, the ratios of oleic and linoleic acids being from the unsaturated fatty acids were observed to be 75.43%, 68.78% and 15.91%, 23.99%, respectively. Beside to the initial analyses, the volatile compounds belonging to the oils were extracted by solid phase microextraction (SPME) technique, and both the qualitative and quantitative analyses were accomplished using the gas chromatography-mass spectrometer (GC-MS). The results show that the amount of Benzaldehyde compound detected as the major amount in both the plum and apricot kernel oils was found to be 48.82x106 AU and 58.40x106 AU, respectively. Oxidative stabilities of cold pressed plum and apricot kernel oils were also evaluated under the thermal and photo-oxidation conditions. The changes of peroxide value and specific extinction coefficients as well as volatile compounds were examined during the oxidation process. At the end of 12th day of storage under the thermal oxidation conditions, the values of peroxide, K232 and K270 coefficients for the oils were recorded as 63.82, 24.41 meq O2/kg; 12.38, 4.75 and 1.98, 0.21, respectively. At the same time, that the aldehydes were observed as the most appeared chemical group with the enhancement of thermal oxidation is obvious. In particular, the hexanal and E-2-heptenal were recorded to be the values of 149.24 x106 AU and 41.83x106 AU for the plum kernel oil after 12 days storage whereas the parameters were noted to reach up to 199.28 x106 AU and 58.88 x106 AU for the apricot kernel oil onlyafter 10 days storage. At the end of 12 days storage under photooxidation of plum and apricot kernel oil, the values of peroxide, K232 and K270 coefficients were measured to be 117.52, 67.62 meq O2/kg, 5.72, 4.56 and 2.29, 0.13, respectively. The aldehydes were assigned as the most chemical groups (especially hexanal and E-2-heptenal) appeared in photooxidised oils. At the end of storage, the hexanal and E-2-heptenal compounds in the plum and apricot oils were determined to be about 48.95 x106 AU, 20.13x106 AU and 100.01 x106 AU, 11.57 x106 AU, respectively. Except from thermal and photo-oxidation conditions, resistant to oxidative stability of oil samples was established at the relatively high temperature value of 110 °C by using Rancimat instrument. Induction periods for the plum and apricot kernel oils were determined as 15.95 and 19.56 h, respectively