Influence of oxygen and copper concentration on lipid oxidation in rapeseed oil

The influence of oxygen concentration and copper on lipid oxidation in rapeseed oil during storage at 40°C was investigated. The oil was stored in air, or with 1.1%, 0.17%, or 0.04% oxygen in the headspace, and 70 or 0.07 ppm copper was added. Volatile oxidation products and oxygen consumption were monitored. Addition of 70 ppm copper to the sample in air resulted in a 70-fold higher hexanal concentration after 35 d of storage, compared to the sample without added copper. The addition of 0.07 ppm copper to the sample stored in air gave a doubled hexanal concentration, compared to the sample without copper, after 35 d of storage. For the samples with 70 ppm copper at 0.17% and 0.04% oxygen, all oxygen was consumed after 7 d of storage. The results show the importance of minimizing the oxygen available for oxidation, especially when pro-oxidants are present. In the sample with 70 ppm added copper, in air, the hexanal increase was 65 times larger than for the same sample in 0.04% oxygen. A comparison of the effect of oxygen or copper on oxidation shows that the addition of 70 ppm copper to the 0.04% oxygen sample gave the same increase in hexanal content as an oxygen increase to 0.17%.