Keten tohumu yağı, ayçiçeği yağı ve zeytinyağının otooksidasyonu sırasında epoksi yağ asitlerinin oluşumunun incelenmesi

Lipids are essential components for providing high quantity of energy and being the main storage source. Light, temperature and oxygen parameters may initiate oxidation and leading to not only taste and odor alteration but also formation of toxic end-products. Oxidation reactions are grouped under four different types of mechanisms; autoxidation, thermoxidation, photoxidation and enzymatic oxidation. Lipid autoxidation, is a free-radical chain reaction which has initiation, propagation and termination steps. Apart from light, temperature and oxygen which are the main factors affecting autoxidation, fatty acid composition, presence of transition metals and antioxidants have an important impact. Hydroperoxides, primary oxidation products, are formed by the abstraction of hydrogen atom from the acly carbon. Due to the saturation degree of fatty acids, hyroperoxide formation rate differs. Linoleic acid formes hyroperoxides 250 times than oleic acid. Epoxy fatty acids (EFAs) formed during hyroperoxide decomposition are one group of toxic end-products of oxidation reactions. They have cyclic structure consisting three atoms. However, knowladge about their formation mechanism is limited which make them to be a study area. Control and non-control models of linseed oil, olive oil and sunflower oil blended repectively with stripped/virgin olive oil at a ratio of 2:1 were defined. The objective of these two models were to see the effect of antioxidants, mainly chlorophyll, on autoxidation. Oil models were subjected to an incubation period of 56 days in total, at dark to obtain the autoxidation conditions. Samples were analyzed fresh and at days 4, 7, 14, 21, 28, 42 and 56. Gas chromatography with flame ionization detector (GC-FID) equipped with a polar CP-Sil 88 column was used for quantification of EFAs in oil models. Peroxide value (PV), p-anisidine value (p- AV), conjugated diene (CD) and conjugated triene (CT) analysis were performed to identify the correlation between EFAs and other oxidation products. Fatty acid composition with respect to oleic acid (C18:1), linoleic acid (C18:2) and linolenic acid (C18:3) was also determined for monitoring the relation with the type of EFAs and rate of oxidation. Chlorophyll content was also measured as it was one of the main parameter to be studied. Chlorophyll pigment of the models blended with virgin olive oil was 6.8 mg/kg oil averagely. This value was approximetly same at the begininng and at the end of incubation period. In the samples blended with stripped olive oil, no chlorophyll pigment was measured. Linseed blends were rich in oleic and linolenic acid whereas sunflower blends included higher amounts of linoleic and oleic acid. Finally, models composed of only olive oil showed the highest amounts of oleic acid. Epoxy fatty acid formation was not observed at significant amounts in stripped models of sunflower and olive oil. At the end of incubation process, total epoxy fatty acid content were ranged between 112.1 to 533.0 μg/g of sample. The stripped linseed and olive oil blend showed the highest amount of EFA formation. This was followed by stripped linseed and virgin olive oil blend (122.92 μg/g of oil). When epoxy fatty acid isomers were considered, it was seen that epoxy stearate was formed from oleic acid, epoxy oleate was formed from linoleic acid and lastly epoxy linoleate from linolenic acid. Within 12 identified EFAs, both cis and trans isomers were existed. Non-control model samples which were blended with virgin olive oil were showed higher formation of cis EFAs. On the other hand, in control model trans formation was higher. No correlation was obtained between p-anisidine value and epoxy fatty acid content by Perason's correlation. Models including linseed oil showed a positive correlation against peroxide value. Additionaly, formation amount of EFAs and hydroperoxides were compared. Results showed, EFA formation was higher even hydroperoxide formation was not high. Conjugated diene and triene amounts were found to be related with epoxy fatty acid formation in stripped linseed-olive oil blend and stripped olive-virgin olive oil blend. This study shows, eventhough peroxide value was not high, epoxy fatty acid formation was showed to be considerably high. EFA formation in high amounts may pose health risks. Further studies should be carried out to determine the epoxy fatty acid formation mechanism and parameters effecting the formation rate.