Effect of initial quality and bioactive compounds content in cold-pressed flaxseed oils on oxidative stability and oxidation products formation during one-month storage with light exposure

Flaxseed oils contain significant amounts of unsaturated fatty acids and, consequently, are susceptible to oxidative process. Additionally, inadequate conditions of storage result in the intensification of unfavorable processes. This problem is becoming more and more serious due to the high intensity of illumination of shop display cases and storage rooms, as well as the exposure to sunlight. Although literature data suggests that light may be an even more important oxidizing agent than oxygen, experiments are mainly focused on the oxidation progress in oils from varied raw materials or the changes in oil characteristics under different storage conditions. The aim of the study was to investigate the effect of the initial state of 30 commercial cold-pressed flaxseed oils on oxidative stability and oxidation product formation during storage under simulated store conditions (one-month at ambient temperature with light exposure). The oil quality was analyzed qualitatively (characteristic quality values, content of conjugated fatty acids, induction period, color parameters) and quantitatively (content of water and bioactive compounds, fatty acid composition). Oxidation progress in the oils was monitored by the characteristic quality values, content of conjugated fatty acids and color parameters.

It was shown that commercially available cold-pressed flaxseed oils were generally good quality with similar color parameters and fatty acid composition, but mostly varied in terms of carotenoids, chlorophylls and phenolic compounds. Storage with light exposure caused the deterioration of the oil quality, and at least a 1.0-fold increase in acid and anisidine values and at least a 24.8-fold increase in peroxide value were determined. Also, the color of all oils changed after storage, and the calculated total color differences (ΔE) were in the range of 0.2–8.7. The results highlighted that the formation of oxidation products in flaxseed oil during storage in light resulted mainly from its initial quality indices. In turn, the induction period tested by Rancimat was dependent on the fatty acid percentages and total phenolic compound content. In conclusion, the Rancimat test is a poor indicator of the oxidative stability of oils under storage at ambient temperature with light exposure.