Monitoring stability and volatile oxidation compounds of cold-pressed flax seed, grape seed and black cumin seed oils upon photo-oxidation

Cold-pressed oils (CPOs), rich in unsaturated fatty acids and bioactive lipids, are considered as healthy oils. Photo-oxidation is a major deterioration reaction for edible oils. In this work, cold-pressed flax (Linum usitatissimum) seed, grape (Vitis vinifera) seed and black cumin (Nigella sativa) seed oils were stored under photo-oxidation conditions for 6 days. The oxidation was monitored by measuring peroxide value (PV), and conjugated diene value (CD). Volatile oxidation compounds (VOOs) were detected using headspace solid-phase micro-extraction (HS-SPME) and capillary gas chromatographic (GC) technique. PV of flax, black cumin and grape seed oils reached up to 87.10, 329.0 and 355.7 meq O2/kg at the end of storage, respectively. CD values in flax seed oil were lower than in grape and black cumin seeds oil during storage. Hexanal was the main compound in flax seed oil during storage while (E)-2-heptenal was detected at the 5th day of storage. Alkadienals including 2,4-hexadienal, and 2,4-heptadienal were formed in flax seed oil after 4 days of storage. Hexanal, (E)-2-heptenal and 2-octenal were the measured aldehydes in grape seed oil. Hexanal and (E)-2-heptenal were the major VOOs from black cumin seed oil during the oxidation experiment. The information obtained in this study are useful in the quality control of CPOs during storage.