Thermal oxidative stability analysis of hoki and tuna oils by Differential Scanning Calorimetry and Thermogravimetry

Abstract

In this study, oxidative stability of hoki and tuna oils were measured at 80°C by Differential Scanning Calorimetry (DSC) and thermogravimetric analysis (TGA) under an air atmosphere. The onset time for oxidation (to) of hoki oil occurred earlier in the TGA (222.50 min) compared to DSC (640.83 min) as the sample gained weight prior to decomposition. Conversely, the to of tuna oil could not be recorded since tuna oil was rapidly oxidized. The predicted shelf life of hoki oil for onset of oxygen uptake and subsequent decomposition at 4°C, by Arrhenius extrapolation of TGA and DSC under different isothermal treatments were 0.56 and 1.39 years, respectively. Temperature programmed decomposition of hoki and tuna oils by TGA occurred in three thermal stages, suggesting a progressive degradation of polyunsaturated fatty acids (PUFA), monounsaturated fatty acids (MUFA), and saturated fatty acids (SFA), followed by volatilization of polymerization and pyrolysis products.Practical applications: Fish oil has been marketed as dietary supplements and as an ingredient for food products. However, these products are susceptible to oxidation due to the high‐PUFA content in fish oil. Oxidative and thermal stability of fish oil are important parameters in the processing and production of fish oil and fish oil fortified food products. These data can be used by fish oil and food manufacturers to optimize processing conditions for fish oil and food products fortified with fish oil. The oxidative stability of fish oils over temperature ranges and storage times can be measured by both isothermal and non‐isothermal DSC and TGA analyses. These techniques are more rapid and provide continuous data compared to conventional shelf life studies and alternative instrumental methods. Shelf life of the fish oils can be predicted by an Arrhenius extrapolation from elevated isothermal DSC and TGA analyses.Measurement of oxidative stability of fish oils by DSC and TGA follow the Q10 law on the relationship between temperature and rate of chemical reaction. Prediction of shelf life of the fish oils is possible by an Arrhenius extrapolation from elevated isothermal DSC and TGA analyses. Differences in the thermal behavior of the fish oils were consistent with major fatty acid compositional differences.