Aims: Today, a part of studies on food science has investigated the effect of cooking methods on the oxidation of various types of meat and the use of natural herbal preservatives instead of synthetic preservatives. The aim of the present study was to evaluate the oxidative stability of pre-cooked rainbow trout (Oncorhynchus mykiss) fillet treated with Dill (Anethum graveolens L.)  essential oil (EOs).
Materials and Methods: In the present experimental research, rainbow trout fillet with dill EOs and Butylated hydroxytoluene (BHT) were treated, each at 3 different concentrations, and cooked by 3 methods, including frying, oven baking, and steaming. The cooked samples were stored at -18◦C for 4 months and analyzed at the end of each month. The extracted oil was used to measure the value of free fatty acid (FFA), peroxide value (PV), and thiobarbituric acid (TBARS). The data were analyzed by SPSS 20, using two-way ANOVA, Tukey's post hoc, Kruskal-Wallis, and Mann-Whitney U tests.
Findings: The FFA formation showed increase in all samples, especially oven baked rainbow trout fillets (p<0.05). The highest value of PV was also obtained from the fried fillets treated by BHT. After cooking, TBARS values in treated samples with essential oil showed decrease in all samples cooked with EOs. FFA, PV, and TBARS increased in all samples, but the samples cooked with EOs had lower FFA, PV, and TBARS than the control samples.
Conclusion: In rainbow trout, the lipid oxidation increases with the thermal process, but the essential oil postpones the oxidation during the storage period as frozen. The samples cooked with Dill EOs have lower amount of FFA, PV, and TBARS compared with the control peers.