Critical evaluation of non-thermal plasma as an innovative accelerated lipid oxidation technique in fish oil

• Non-thermal plasma (NTP) accelerates lipid oxidation in fish oil at ambient temperatures.
• Application of NTP is promising in the field of lipid oxidation chemistry and antioxidant testing.
• Plasma oxidation is compared with natural and thermally induced lipid oxidation.

Food products enriched with healthier unsaturated fatty acids are more sensitive to lipid oxidation, leading to an overall quality deterioration and the development of unwanted aroma properties. To evaluate the oxidative stability a wide range of techniques has been described in literature, of which most are thermally based. These unrealistic test conditions result in the induction of deviating oxidation chemistry compared to that observed during ambient storage. Non-thermal plasma technology is capable to generate a wide range of highly reactive oxidative species (e.g. atomic oxygen, hydroxyl radicals, singlet oxygen) while maintaining ambient temperatures. For the first time, a DBD-plasma jet (Ar/0.6% O2) is used on fish oil samples as a faster and more realistic accelerated lipid oxidation method. This paper critically evaluates both a thermal as a non-thermal plasma based accelerated oxidation protocol using naturally aged fish oil as reference. Experiments were done using both virgin, as alpha-tocopherol-enriched fish oil samples. Secondary lipid oxidation volatiles were measured using HS-SPME–GC–MS. Both accelerated oxidation techniques induced the formation of typical lipid oxidation markers (e.g. 2-propenal, (E)-2-pentenal, heptanal), however in both cases significant differences were observed compared to the naturally aged fish oil. On the other side, non-thermal plasma correctly predicted an antioxidative effect when 1000 μg/g alpha-tocopherol was added to the fish oil, while thermally based tests resulted in the induction of prooxidative chemistry. Despite the differences with naturally aged fish oil, several non-thermal plasma characteristics (reactor configuration, gas feed mixture, power source, …) can be fine-tuned to evolve towards a technology that is capable to accelerate lipid oxidation in a highly realistic manner.