Evaluation of oxygen partial pressure, temperature and stripping of antioxidants for accelerated shelf-life testing of oil blends using ¹H NMR

Lipid oxidation compromises the shelf-life of lipid-containing foods, leading to the generation of unpleasant off-flavours. Monitoring lipid oxidation under normal shelf-life conditions can be time-consuming (i.e. weeks or months) and therefore accelerated shelf-life conditions are often applied. However, little is known on their impact on the lipid oxidation mechanisms. In this study, different oxygen partial pressures (P_O2; 10 and 21%), temperatures (20, 30 and 40 °C), and the removal of antioxidants through stripping of the oil were tested to accelerate lipid oxidation. Increasing the incubation temperature of stripped oil blends from 30 to 40 °C reduced the onset of lipid oxidation from 4 to 2 weeks, whereas the P_O2 had no impact. Surprisingly, at room temperature, an increase in P_O2 resulted in a longer onset time (10 weeks under 10% oxygen, 15 weeks under 21% oxygen). We hypothesize that this is due to a shift in (initiation) mechanism. In non-stripped oil, an increase in P_O2 from 10 to 21% decreased the onset time from 16 to 10 weeks (40 °C). Temperature elevations and stripping led to a shift towards more trans–trans diene hydroperoxides, as compared to the cis–trans conformation. Additionally, oil stripping led to an increase in oxidized PUFAs with three or more double bonds in which the hydroperoxide group is located between the double bond pattern, instead of on the edge of it. Lastly, it was shown that small additions of LC-PUFAs (0, 0.3, 0.6, 1.2 and 2.3%, w/w) accelerate lipid oxidation, even in relatively stable stripped oils. In conclusion, increased P_O2 and slightly elevated temperatures hold fair potential for accelerated shelf-life testing of non-stripped oils with a limited impact on the lipid oxidation mechanisms, whereas stripping significantly changes propagation mechanisms.