Critical evaluation of thermal and non-thermal accelerated lipid oxidation in fish oil

Today saturated lipids in food are increasingly replaced by healthier unsaturated lipids. These new lipid-rich food products are more susceptible to lipid oxidation resulting in the formation of undesired flavors and aromas. Fish oil is one of the most oxidative instable products due to its high content of polyunsaturated fatty acids, such as DHA and EPA. The development of undesired organoleptic changes in fish oil is often noticeable after a few days or weeks. To study these oxidative lipid mechanisms in a faster manner, accelerated oxidation tests are required. Today most accelerated lipid oxidation tests are based on increasing temperature (e.g. Rancimat approach). However, several studies indicate a poor correlation with natural lipid oxidation mechanisms due to widely divergent kinetics in function of the employed temperature. Recent studies also show that antioxidant properties can be falsely interpreted when applying elevated temperatures. In this study a-tocopherol was added to fish oil. Both standard fish oil, as the enriched matrix, were exposed to different thermal conditions for accelerated oxidation. In this work volatile organic compounds were measured as markers for fish oil oxidation. A natural aging test was set up by storing a sample of fresh fish oil in the dark at ambient temperature. This test was used as a reference to evaluate the above-mentioned accelerated oxidation methods. Additionally, in this study a highly innovative technique, non-thermal plasma technology, was applied on the fish oil matrices. Recently, Van Durme et al. (2014) published that Non-thermal Plasma might have the potential to study lipid oxidation mechanisms in an faster manner at moderate conditions, hence possibly inducing changes closer to natural oxidation mechanisms. Fish oil samples were treated with a radio-frequency plasma jet (0.3% O2/Argon plasma). First results of this highly innovative technique will be discussed for fish oil, with and without a-tocopherol, and compared with both the discussed thermally-based and natural oxidation tests.status: publishe